ArnF (formerly PmrM/YfbJ) is a subunit of the undecaprenyl phosphate-alpha-L-Ara4N flippase, forming a heterodimer with ArnE that translocates 4-amino-4-deoxy-L-arabinose-phosphoundecaprenol (alpha-L-Ara4N-phosphoundecaprenol) from the cytoplasmic to the periplasmic side of the inner membrane [PMID:17928292]. This flipping step is essential for L-Ara4N modification of lipid A by ArnT (whose active site faces the periplasm), which confers resistance to polymyxin and cationic antimicrobial peptides. ArnF is a 128 AA inner membrane protein with 4 transmembrane helices, distantly related to EmrE and other members of the DMT/SMR superfamily. It is part of the arnBCADTEF operon, regulated by BasR in response to iron and other environmental stimuli [PMID:15569938].
Definition: Enables the directional transport of a lipid from one leaflet of a membrane to the other leaflet, without coupling to ATP hydrolysis. Unlike scramblases, the transport is directional and substrate-specific.
Justification: The current GO hierarchy under GO:0140303 (intramembrane lipid transporter activity) has two children -- ATPase-coupled intramembrane lipid transporter activity (GO:0140326, parent of flippase/floppase) and phospholipid scramblase activity (GO:0017128, ATP-independent but non-selective/bidirectional). ArnE/ArnF and possibly other bacterial undecaprenyl-linked sugar flippases are directional and substrate-specific but not ATP-dependent, falling in a gap between these two branches. GO:0015161 (lipid III floppase activity) is the closest analog but is classified as ATP-dependent under floppase activity.
Parent term: intramembrane lipid transporter activity
Supporting Evidence:
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
|
GO:0022857
transmembrane transporter activity
|
IBA
GO_REF:0000033 |
MODIFY |
Summary: ArnF is a subunit of the undecaprenyl phosphate-alpha-L-Ara4N flippase, which translocates a lipid-linked sugar across the inner membrane [PMID:17928292]. This is technically an intramembrane lipid transporter (flipping a lipid-linked substrate from one leaflet to the other), rather than a classical transmembrane transporter that moves solutes across the membrane. The IBA annotation to the parent term 'transmembrane transporter activity' captures the general transporter function, which is phylogenetically sound given the SMR/DMT superfamily membership.
Reason: While ArnF is part of the transporter superfamily (DMT/SMR) and the IBA annotation is phylogenetically reasonable, 'transmembrane transporter activity' (GO:0022857) is too generic and does not capture the specific intramembrane lipid flipping function. The more accurate term is GO:0140303 'intramembrane lipid transporter activity', which describes transport of a lipid from one region of a membrane to a different region on the same membrane -- precisely the flippase function demonstrated for ArnF [PMID:17928292].
Proposed replacements:
intramembrane lipid transporter activity
Supporting Evidence:
PMID:17928292
PmrL and PmrM could specifically function to flip undecaprenyl phosphate-alpha-L-Ara4N from the cytosolic to the periplasmic side of the inner membrane, possibly functioning as a heterodimer
|
|
GO:0005886
plasma membrane
|
IBA
GO_REF:0000033 |
ACCEPT |
Summary: ArnF is an inner membrane protein in E. coli. In GO, the E. coli inner membrane (cytoplasmic membrane) is annotated as 'plasma membrane' (GO:0005886), which is correct usage for bacteria. This is supported by experimental evidence from topology analysis [PMID:15919996] and is consistent with its function as a flippase in the inner membrane [PMID:17928292].
Reason: The IBA annotation to plasma membrane is correct. ArnF is an integral inner membrane protein with 4 transmembrane helices, confirmed by global topology analysis. In bacterial GO annotation, the inner/cytoplasmic membrane is properly annotated as plasma membrane (GO:0005886).
Supporting Evidence:
PMID:15919996
Global topology analysis of the Escherichia coli inner membrane proteome
PMID:17928292
PmrL and PmrM are small, hydrophobic, inner membrane proteins with many of the characteristics of small multidrug resistance transporters. Both PmrL and PmrM are predicted to have four membrane-spanning helices
|
|
GO:0055085
transmembrane transport
|
IBA
GO_REF:0000033 |
ACCEPT |
Summary: ArnF participates in the translocation of undecaprenyl phosphate-alpha-L-Ara4N across the inner membrane [PMID:17928292]. This is an intramembrane translocation (flipping from one leaflet to the other) rather than a transmembrane transport event in the classical sense of moving a solute from one aqueous compartment to another. The IBA annotation captures the general transport process from the SMR family phylogenetic context.
Reason: While the precise mechanism is intramembrane lipid flipping rather than classical transmembrane transport of a solute, GO:0055085 'transmembrane transport' is a reasonable process term for this function since the substrate does cross the membrane bilayer. The IBA inference from the SMR/DMT family is phylogenetically sound. The existing experimental IMP annotations to more specific terms (GO:1901264 carbohydrate derivative transport) complement this broader annotation.
Supporting Evidence:
PMID:17928292
The data imply that both PmrL and PmrM are involved in the translocation of undecaprenyl phosphate-alpha-LAra4N across the inner membrane
|
|
GO:0005886
plasma membrane
|
IEA
GO_REF:0000120 |
ACCEPT |
Summary: Automated annotation to plasma membrane. ArnF is confirmed as an inner membrane protein (equivalent to plasma membrane in bacteria) by both experimental topology studies [PMID:15919996] and by its established function as a flippase in the inner membrane [PMID:17928292].
Reason: This IEA annotation is correct and is independently supported by IDA evidence (PMID:15919996) and IBA evidence (GO_REF:0000033). Duplicating the more specific experimental annotation is acceptable for IEA.
Supporting Evidence:
PMID:15919996
Global topology analysis of the Escherichia coli inner membrane proteome
|
|
GO:0006629
lipid metabolic process
|
IEA
GO_REF:0000043 |
ACCEPT |
Summary: Automated annotation from UniProt keyword mapping. ArnF's primary function is as a flippase for lipid-linked sugar substrates, participating in the L-Ara4N lipid A modification pathway [PMID:17928292]. While ArnF is involved in the overall pathway of lipid A modification, calling its specific function 'lipid metabolic process' is very broad.
Reason: While this is a very broad term, it is not incorrect. ArnF participates in a lipid metabolic pathway (lipid A modification) by translocating a lipid-linked substrate. The UniProt keywords include 'Lipid biosynthesis' and 'Lipid metabolism' which map to this term. More specific BP annotations (GO:0046493 lipid A metabolic process, GO:0009245 lipid A biosynthetic process) are also present and provide the necessary specificity. This IEA serves as a broader parent annotation.
Supporting Evidence:
PMID:17928292
We propose that PmrL and PmrM be renamed ArnE and ArnF, respectively (Fig. 2B), given their function in generating L-Ara4N modified lipid A species
|
|
GO:0009103
lipopolysaccharide biosynthetic process
|
IEA
GO_REF:0000120 |
ACCEPT |
Summary: Automated annotation to LPS biosynthesis. ArnF is part of the arn operon which is involved in modifying lipid A (the lipid component of LPS) with L-Ara4N [PMID:17928292]. UniProt explicitly lists this under PATHWAY as 'Bacterial outer membrane biogenesis; lipopolysaccharide biosynthesis'.
Reason: ArnF functions in the L-Ara4N modification of lipid A, which is a component of lipopolysaccharide. The LPS biosynthetic process term appropriately captures the pathway context. This is consistent with the UniProt pathway annotation and the established role of the arn operon in LPS modification.
Supporting Evidence:
PMID:17928292
Modification of lipid A with the 4-amino-4-deoxy-L-arabinose (L-Ara4N) moiety is required for resistance to polymyxin and cationic antimicrobial peptides in Escherichia coli and Salmonella typhimurium
|
|
GO:0009245
lipid A biosynthetic process
|
IEA
GO_REF:0000120 |
ACCEPT |
Summary: Automated annotation to lipid A biosynthesis. ArnF participates in the L-Ara4N modification of lipid A, which is a post-biosynthetic modification rather than de novo lipid A biosynthesis [PMID:17928292]. The more precise term would be GO:0046493 'lipid A metabolic process' (which is already annotated via IMP), since ArnF is involved in modifying existing lipid A rather than synthesizing it de novo.
Reason: While strictly speaking ArnF participates in lipid A modification rather than de novo lipid A biosynthesis, the L-Ara4N modification pathway is conventionally grouped under lipid A biosynthesis in the broader sense of generating the final modified lipid A species. UniProt keywords include 'Lipid A biosynthesis', and this annotation is broadly consistent. The IMP annotation to GO:0046493 (lipid A metabolic process) provides a more accurate complementary annotation.
Supporting Evidence:
PMID:17928292
In the pmrL or pmrM deletion mutants, over 95% of each of the L-Ara4N-modified lipid A species was missing
|
|
GO:0016020
membrane
|
IEA
GO_REF:0000002 |
ACCEPT |
Summary: InterPro-based annotation to the generic 'membrane' component. ArnF is an integral membrane protein with 4 transmembrane helices located in the inner (plasma) membrane. This is correct but much less specific than the plasma membrane annotations already present.
Reason: This is a correct but very broad cellular component annotation. ArnF is unquestionably a membrane protein (4 TM helices, integral inner membrane protein). While GO:0005886 (plasma membrane) is more informative and is already annotated via IBA, IDA, and IEA, keeping this broader IEA annotation is acceptable as it provides the InterPro-derived evidence.
Supporting Evidence:
PMID:17928292
A BLASTp analysis of PmrL and PmrM shows that both are small integral membrane proteins with four putative trans-membrane helices
|
|
GO:0022857
transmembrane transporter activity
|
IEA
GO_REF:0000120 |
MODIFY |
Summary: Automated annotation to transmembrane transporter activity. ArnF is a subunit of the undecaprenyl phosphate-alpha-L-Ara4N flippase [PMID:17928292], which functions as an intramembrane lipid transporter rather than a classical transmembrane transporter. This IEA parallels the IBA annotation to the same term.
Reason: This IEA annotation to GO:0022857 is the same term as the IBA annotation. As with the IBA, 'transmembrane transporter activity' is too generic for ArnF's specific intramembrane lipid flipping function. The more accurate term is GO:0140303 'intramembrane lipid transporter activity', which precisely describes the flippase function demonstrated for ArnF [PMID:17928292].
Proposed replacements:
intramembrane lipid transporter activity
Supporting Evidence:
PMID:17928292
PmrL and PmrM could specifically function to flip undecaprenyl phosphate-alpha-L-Ara4N from the cytosolic to the periplasmic side of the inner membrane, possibly functioning as a heterodimer
|
|
GO:0055085
transmembrane transport
|
IEA
GO_REF:0000104 |
ACCEPT |
Summary: Automated annotation to transmembrane transport, transferred from manual annotations on related proteins via shared sequence features. This parallels the IBA annotation to the same BP term and is broadly consistent with ArnF's role in translocating undecaprenyl phosphate-alpha-L-Ara4N across the inner membrane [PMID:17928292].
Reason: This IEA annotation is consistent with the IBA annotation to the same term and is supported by the experimental evidence for ArnF's flippase function. As an automated annotation it provides an acceptable broader process term.
Supporting Evidence:
PMID:17928292
The data imply that both PmrL and PmrM are involved in the translocation of undecaprenyl phosphate-alpha-LAra4N across the inner membrane
|
|
GO:1901505
carbohydrate derivative transmembrane transporter activity
|
IEA
GO_REF:0000002 |
ACCEPT |
Summary: InterPro-based annotation to carbohydrate derivative transmembrane transporter activity. The substrate of ArnF is undecaprenyl phosphate-alpha-L-Ara4N, which contains L-Ara4N (4-amino-4-deoxy-L-arabinose), a carbohydrate derivative. This term is more specific than generic transmembrane transporter activity and captures the carbohydrate-linked nature of the substrate [PMID:17928292].
Reason: This annotation is accurate -- the substrate translocated by the ArnE/ArnF flippase is undecaprenyl phosphate-alpha-L-Ara4N, which is a carbohydrate derivative (containing L-Ara4N, a modified arabinose). This is more informative than the generic 'transmembrane transporter activity' and is consistent with the IMP annotation to the same term from PMID:17928292.
Supporting Evidence:
PMID:17928292
PmrL and PmrM could specifically function to flip undecaprenyl phosphate-alpha-L-Ara4N from the cytosolic to the periplasmic side of the inner membrane
|
|
GO:0046493
lipid A metabolic process
|
IMP
PMID:17928292 An undecaprenyl phosphate-aminoarabinose flippase required f... |
ACCEPT |
Summary: In-frame deletion of arnF (pmrM) in a pmrAc background results in loss of over 95% of L-Ara4N-modified lipid A species, demonstrating that ArnF is required for lipid A modification [PMID:17928292]. The mutant phenotype (loss of lipid A modification, polymyxin sensitivity) directly implicates ArnF in the lipid A metabolic process.
Reason: This IMP annotation is well-supported by the deletion phenotype data in Yan et al. 2007. The arnF deletion mutant lacks L-Ara4N modified lipid A, demonstrating a clear role in lipid A metabolism. This is a core process annotation for ArnF.
Supporting Evidence:
PMID:17928292
In the pmrL or pmrM deletion mutants, over 95% of each of the L-Ara4N-modified lipid A species was missing
PMID:17928292
the pmrL and the pmrM deletion mutants (as well as the double deletion mutant) were sensitive to 15 μg/ml polymyxin
|
|
GO:0010041
response to iron(III) ion
|
IGI
PMID:12139617 Fe(III)-mediated cellular toxicity. |
MARK AS OVER ANNOTATED |
Summary: This annotation is based on Chamnongpol et al. 2002 which studied Fe(III)-mediated toxicity and the PmrA/PmrB system. The study showed that the PmrA/PmrB system (which regulates the arn operon including arnF) is important for Fe(III) resistance. However, arnF's connection to iron response is indirect -- iron activates BasS/BasR (PmrA/PmrB homolog), which induces the arn operon, leading to lipid A modification. ArnF itself does not sense or directly respond to iron; it is merely transcriptionally induced as part of a regulon. The IGI evidence code suggests genetic interaction, but the gene's role is downstream in the effector pathway rather than in iron sensing or response per se.
Reason: The 'response to iron(III) ion' annotation conflates transcriptional regulation with gene function. ArnF is a lipid flippase whose expression happens to be induced by iron via the BasS-BasR two-component system. The gene does not directly sense, bind, or respond to iron. Many genes in stress-induced regulons would receive inappropriate 'response to X' annotations if mere transcriptional induction were sufficient. The PMID:12139617 study focused on PmrA/PmrB-dependent Fe(III) resistance mechanisms but did not specifically demonstrate a direct role for arnF in iron response. The connection is via operon co-regulation, not direct function.
Supporting Evidence:
PMID:12139617
Fe(III) exerts its microbicidal activity by a mechanism that is oxygen independent and different from that mediated by Fe(II)
PMID:15322361
the BasS-BasR system is essential for this iron-dependent induction of yfbE
|
|
GO:1901264
carbohydrate derivative transport
|
IMP
PMID:17928292 An undecaprenyl phosphate-aminoarabinose flippase required f... |
ACCEPT |
Summary: The arnF deletion mutant shows 4-5 fold reduced accessibility of undecaprenyl phosphate-alpha-L-Ara4N to membrane-impermeable sulfo-NHS-biotin labeling, while total levels of the substrate are unchanged [PMID:17928292]. This demonstrates that ArnF is required for transport of this carbohydrate derivative (L-Ara4N-linked lipid) across the inner membrane. The substrate undecaprenyl phosphate-alpha-L-Ara4N contains L-Ara4N (a carbohydrate derivative), making this term appropriate.
Reason: This IMP annotation accurately describes the biological process. The sulfo-NHS-biotin accessibility assay in Yan et al. 2007 provides direct evidence that ArnF is involved in transporting the carbohydrate derivative undecaprenyl phosphate-alpha-L-Ara4N across the membrane. This is a core process for ArnF.
Supporting Evidence:
PMID:17928292
At the 4-h time point, there was a 4-5-fold reduction in ratio of the monoisotopic peak areas for biotinylated undecaprenyl phosphate-alpha-L-Ara4N compared with unmodified undecaprenyl phosphate-alpha-L-Ara4N
PMID:17928292
undecaprenyl phosphate-alpha-L-Ara4N levels were the same or slightly higher in the mutants than in the parent, indicating that appropriate amounts of the prenol lipid donor of the L-Ara4N moiety are still synthesized in these mutants
|
|
GO:1901505
carbohydrate derivative transmembrane transporter activity
|
IMP
PMID:17928292 An undecaprenyl phosphate-aminoarabinose flippase required f... |
ACCEPT |
Summary: Experimental evidence from the sulfo-NHS-biotin accessibility assay demonstrates that ArnF is required for translocating undecaprenyl phosphate-alpha-L-Ara4N (a carbohydrate derivative) across the inner membrane [PMID:17928292]. The arnF mutant shows reduced periplasmic accessibility of the substrate while total levels remain unchanged, consistent with impaired transporter function. Complementation with pWSK29-PmrM restores polymyxin resistance, confirming the specific role of ArnF [PMID:17928292].
Reason: This MF annotation is well-supported by the experimental data in Yan et al. 2007. The sulfo-NHS-biotin assay demonstrates transporter activity for a carbohydrate derivative substrate. The complementation experiment confirms gene-specific function. This represents a core molecular function of ArnF.
Supporting Evidence:
PMID:17928292
The data imply that both PmrL and PmrM are involved in the translocation of undecaprenyl phosphate-alpha-LAra4N across the inner membrane
PMID:17928292
polymyxin resistance was recovered in the pmrM deletion mutant AY101 by transforming with pWSK29-PmrM
|
|
GO:0005886
plasma membrane
|
IDA
PMID:15919996 Global topology analysis of the Escherichia coli inner membr... |
ACCEPT |
Summary: Daley et al. 2005 performed a global topology analysis of the E. coli inner membrane proteome using C-terminal GFP/PhoA fusions. ArnF (YfbJ) was among the 601 inner membrane proteins characterized, with C-terminal tagging establishing its inner membrane localization [PMID:15919996]. In bacterial GO annotation, the inner membrane is annotated as plasma membrane (GO:0005886).
Reason: This IDA annotation is based on direct experimental evidence from GFP/PhoA topology analysis. The C-terminal fusion approach provides reliable evidence for inner membrane localization. This is the strongest evidence for the cellular component annotation and represents a core localization for ArnF.
Supporting Evidence:
PMID:15919996
Using C-terminal tagging with the alkaline phosphatase and green fluorescent protein, we established the periplasmic or cytoplasmic locations of the C termini for 601 inner membrane proteins
|
|
GO:0010041
response to iron(III) ion
|
IEP
PMID:15322361 A Genome-wide view of the Escherichia coli BasS-BasR two-com... |
MARK AS OVER ANNOTATED |
Summary: Hagiwara et al. 2004 used genome-wide transcriptome profiling to show that the yfbE operon (now arn operon, including arnF) is induced in response to external iron via the BasS-BasR two-component system [PMID:15322361]. The IEP evidence code (Inferred from Expression Pattern) is technically appropriate for a gene whose expression changes in response to iron. However, as with the IGI annotation above, this annotation conflates transcriptional regulation with direct functional involvement in iron response. ArnF's function is lipid flipping, not iron sensing.
Reason: The IEP evidence code is technically appropriate -- arnF expression is induced by iron via the BasS-BasR system. However, annotating a gene to 'response to iron(III) ion' based solely on transcriptional induction conflates regulation with function. ArnF is a flippase that translocates undecaprenyl phosphate-alpha-L-Ara4N; it does not participate in iron sensing, binding, or detoxification. Many genes in iron-responsive regulons (e.g., house-keeping genes in Fur regulon) would be similarly over-annotated. The annotation is not wrong in the strict GO sense (the protein is produced in response to iron), but it does not represent a core function and is misleading about ArnF's actual role.
Supporting Evidence:
PMID:15322361
the BasS-BasR system is essential for this iron-dependent induction of yfbE
PMID:15322361
the hypothetical yfbE operon that appears to be implicated in the modification of lipopolysaccharides is regulated at the level of transcription in response to external iron
|
|
GO:0140303
intramembrane lipid transporter activity
|
IMP
PMID:17928292 An undecaprenyl phosphate-aminoarabinose flippase required f... |
NEW |
Summary: ArnF functions as a subunit of a flippase that translocates undecaprenyl phosphate-alpha-L-Ara4N from the cytoplasmic to the periplasmic leaflet of the inner membrane [PMID:17928292]. This is specifically an intramembrane lipid transport event -- the lipid-linked substrate is moved from one leaflet to the other within the same membrane, not transported across the membrane into solution. GO:0140303 (intramembrane lipid transporter activity) precisely captures this function.
Reason: This term is more specific and accurate for ArnF's molecular function than the existing GO:0022857 (transmembrane transporter activity) or GO:1901505 (carbohydrate derivative transmembrane transporter activity). The sulfo-NHS-biotin accessibility assay in Yan et al. 2007 directly demonstrates that ArnF is required for moving undecaprenyl phosphate-alpha-L-Ara4N to the periplasmic face of the inner membrane -- an intramembrane lipid translocation event. This should be considered a core MF annotation for ArnF.
Supporting Evidence:
PMID:17928292
PmrL and PmrM could specifically function to flip undecaprenyl phosphate-alpha-L-Ara4N from the cytosolic to the periplasmic side of the inner membrane, possibly functioning as a heterodimer
PMID:17928292
At the 4-h time point, there was a 4-5-fold reduction in ratio of the monoisotopic peak areas for biotinylated undecaprenyl phosphate-alpha-L-Ara4N compared with unmodified undecaprenyl phosphate-alpha-L-Ara4N
file:ECOLI/arnF/arnF-deep-research-falcon.md
ArnE/ArnF are placed as the flipping step between donor synthesis (ArnB/C/A/D) and transfer to lipid A (ArnT) in the L-Ara4N modification pathway
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template_variables:
organism: ECOLI
gene_id: arnF
gene_symbol: arnF
uniprot_accession: P76474
protein_description: 'RecName: Full=Probable 4-amino-4-deoxy-L-arabinose-phosphoundecaprenol
flippase subunit ArnF; Short=L-Ara4N-phosphoundecaprenol flippase subunit ArnF;
AltName: Full=Undecaprenyl phosphate-aminoarabinose flippase subunit ArnF;'
gene_info: Name=arnF; Synonyms=pmrM, yfbJ; OrderedLocusNames=b2258, JW5373;
organism_full: Escherichia coli (strain K12).
protein_family: Belongs to the ArnF family. .
protein_domains: EmrE-like. (IPR037185); Flippase_ArnF. (IPR022832); Small_drug/metabolite_transptr.
(IPR000390)
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BEFORE YOU BEGIN RESEARCH: You MUST verify you are researching the CORRECT gene/protein. Gene symbols can be ambiguous, especially for less well-characterized genes from non-model organisms.
DO NOT PROCEED WITH RESEARCH ON A DIFFERENT GENE. Instead:
- State clearly: "The gene symbol 'arnF' is ambiguous or literature is limited for this specific protein"
- Explain what you found (e.g., "Found extensive literature on a different gene with the same symbol in a different organism")
- Describe the protein based ONLY on the UniProt information provided above
- Suggest that the protein function can be inferred from domain/family information
Please provide a comprehensive research report on the gene arnF (gene ID: arnF, UniProt: P76474) in ECOLI.
The research report should be a detailed narrative explaining the function, biological processes, and localization of the gene product. Citations should be given for all claims.
You should prioritize authoritative reviews and primary scientific literature when conducting research. You can supplement
this with annotations you find in gene/protein databases, but these can be outdated or inaccurate.
We are specifically interested in the primary function of the gene - for enzymes, what reaction is catalyzed, and what is the substrate specificity? For transporters, what is the substrate? For structural proteins or adapters, what is the broader structural role? For signaling molecules, what is the role in the pathway.
We are interested in where in or outside the cell the gene product carries out its function.
We are also interested in the signaling or biochemical pathways in which the gene functions. We are less interested in broad pleiotropic effects, except where these elucidate the precise role.
Include evidence where possible. We are interested in both experimental evidence as well as inference from structure, evolution, or bioinformatic analysis. Precise studies should be prioritized over high-throughput, where available.
Question: You are an expert researcher providing comprehensive, well-cited information.
Provide detailed information focusing on:
1. Key concepts and definitions with current understanding
2. Recent developments and latest research (prioritize 2023-2024 sources)
3. Current applications and real-world implementations
4. Expert opinions and analysis from authoritative sources
5. Relevant statistics and data from recent studies
Format as a comprehensive research report with proper citations. Include URLs and publication dates where available.
Always prioritize recent, authoritative sources and provide specific citations for all major claims.
BEFORE YOU BEGIN RESEARCH: You MUST verify you are researching the CORRECT gene/protein. Gene symbols can be ambiguous, especially for less well-characterized genes from non-model organisms.
DO NOT PROCEED WITH RESEARCH ON A DIFFERENT GENE. Instead:
- State clearly: "The gene symbol 'arnF' is ambiguous or literature is limited for this specific protein"
- Explain what you found (e.g., "Found extensive literature on a different gene with the same symbol in a different organism")
- Describe the protein based ONLY on the UniProt information provided above
- Suggest that the protein function can be inferred from domain/family information
Please provide a comprehensive research report on the gene arnF (gene ID: arnF, UniProt: P76474) in ECOLI.
The research report should be a detailed narrative explaining the function, biological processes, and localization of the gene product. Citations should be given for all claims.
You should prioritize authoritative reviews and primary scientific literature when conducting research. You can supplement
this with annotations you find in gene/protein databases, but these can be outdated or inaccurate.
We are specifically interested in the primary function of the gene - for enzymes, what reaction is catalyzed, and what is the substrate specificity? For transporters, what is the substrate? For structural proteins or adapters, what is the broader structural role? For signaling molecules, what is the role in the pathway.
We are interested in where in or outside the cell the gene product carries out its function.
We are also interested in the signaling or biochemical pathways in which the gene functions. We are less interested in broad pleiotropic effects, except where these elucidate the precise role.
Include evidence where possible. We are interested in both experimental evidence as well as inference from structure, evolution, or bioinformatic analysis. Precise studies should be prioritized over high-throughput, where available.
The target protein is ArnF from Escherichia coli (strain K-12), encoded by arnF with synonyms pmrM and yfbJ (UniProt P76474). The canonical experimental paper explicitly studies E. coli pmrM and states that PmrM is renamed ArnF as part of the L-Ara4N lipid A modification pathway, matching the UniProt description and family/domain expectations (small EmrE-like membrane protein; predicted multi-pass transporter) (yan2007anundecaprenylphosphateaminoarabinose pages 1-2, yan2007anundecaprenylphosphateaminoarabinose pages 5-7).
ArnF is an inner-membrane flippase subunit that functions with ArnE (formerly PmrL) to translocate the lipid-linked donor of 4-amino-4-deoxy-L-arabinose (L-Ara4N, also written Ara4N) across the inner membrane. The donor substrate is undecaprenyl phosphate–α-L-Ara4N (also written Und-P–L-Ara4N or C55P-Ara4N), synthesized on the cytoplasmic face and needed on the periplasmic face for transfer to lipid A (yan2007anundecaprenylphosphateaminoarabinose pages 1-2, yan2007anundecaprenylphosphateaminoarabinose pages 2-4, yan2007anundecaprenylphosphateaminoarabinose media 73fe93bb).
Ara4N modification is a Gram-negative envelope remodeling pathway that reduces the net negative charge of lipid A and thereby reduces binding/efficacy of cationic antimicrobial peptides (CAMPs) including polymyxins (polymyxin B, colistin) (baijal2024polyphosphatekinaseregulates pages 3-5, baijal2024polyphosphatekinaseregulates pages 1-2).
A widely used mechanistic model (supported by genetics/biochemistry) is:
1. Arn enzymes synthesize the lipid-linked Ara4N donor (Und-P/C55P-Ara4N) on the cytosolic leaflet (baijal2024polyphosphatekinaseregulates pages 3-5, munozescudero2023structureandfunction pages 1-2).
2. ArnE/ArnF flip/translocate the donor to the periplasmic leaflet (yan2007anundecaprenylphosphateaminoarabinose pages 1-2, yan2007anundecaprenylphosphateaminoarabinose pages 2-4, yan2007anundecaprenylphosphateaminoarabinose media 73fe93bb).
3. ArnT transfers Ara4N from Und-P/C55P-Ara4N to lipid A on the periplasmic face of the inner membrane (tavarescarreon2016arntproteinsthat pages 2-3, baijal2024polyphosphatekinaseregulates pages 3-5).
The experimentally implicated substrate for the ArnE/ArnF system is undecaprenyl phosphate–α-L-Ara4N (C55P-Ara4N) (yan2007anundecaprenylphosphateaminoarabinose pages 1-2, yan2007anundecaprenylphosphateaminoarabinose pages 2-4).
Yan et al. (2007; published Dec 2007; URL https://doi.org/10.1074/jbc.m706172200) showed that in arnF (pmrM) mutants, total cellular levels of the donor lipid are not reduced, but the donor is less accessible on the periplasmic surface of the inner membrane as measured by labeling with an inner-membrane–impermeable reagent (sulfo-NHS-biotin) (yan2007anundecaprenylphosphateaminoarabinose pages 1-2, yan2007anundecaprenylphosphateaminoarabinose pages 2-4).
Quantitative evidence (directly supporting “flipping/translocation”): the sulfo-NHS-biotin labeling signal for the donor lipid is reduced ~4–5-fold in arnF (pmrM) and arnE (pmrL) mutants (yan2007anundecaprenylphosphateaminoarabinose pages 1-2, yan2007anundecaprenylphosphateaminoarabinose pages 2-4). In the paper’s labeled-MS quantification, the reported area ratios are 0.069 (parent) versus 0.013 (arnF/pmrM mutant) and 0.015 (arnE/pmrL mutant) (yan2007anundecaprenylphosphateaminoarabinose media 80f295c9).
In the same study, in-frame deletion of arnF/pmrM (and arnE/pmrL) in an Ara4N-inducing background eliminates Ara4N-modified lipid A species:
- “Over 95%” of Ara4N-modified lipid A species are missing in the arnE/arnF mutants by ESI/MS lipid A profiling (yan2007anundecaprenylphosphateaminoarabinose pages 7-8).
- Importantly, the donor lipid (C55P-Ara4N) still accumulates to similar or slightly higher levels, consistent with a block after donor synthesis but before transfer to lipid A (yan2007anundecaprenylphosphateaminoarabinose pages 7-8).
Loss of arnF/pmrM converts a polymyxin-resistant phenotype to polymyxin-sensitive. Yan et al. report that arnE or arnF deletions render strains sensitive at 15 μg/mL polymyxin, and complementation restores resistance (yan2007anundecaprenylphosphateaminoarabinose pages 7-8).
ArnF is an integral inner membrane protein implicated in transbilayer movement of the undecaprenyl-linked Ara4N donor; the biochemical accessibility assay specifically interprets reduced periplasmic labeling as failure to concentrate/expose the donor at the periplasmic face (yan2007anundecaprenylphosphateaminoarabinose pages 1-2, yan2007anundecaprenylphosphateaminoarabinose pages 2-4).
ArnF (PmrM) is described as a small (~128 aa) hydrophobic membrane protein predicted to contain four transmembrane helices, with a hydropathy profile resembling the small multidrug transporter EmrE (an SMR-family fold), consistent with a compact transporter/flippase subunit rather than a soluble enzyme (yan2007anundecaprenylphosphateaminoarabinose pages 5-7).
Functional genetics indicates ArnF works with ArnE (formerly PmrL) as a two-protein flippase system (often described as a heterodimer), because deletion of either yields the same “donor present but not periplasmically accessible / no Ara4N-lipid A” phenotype (yan2007anundecaprenylphosphateaminoarabinose pages 1-2, yan2007anundecaprenylphosphateaminoarabinose pages 7-8, yan2007anundecaprenylphosphateaminoarabinose media 73fe93bb).
Muñoz-Escudero et al. (Biochemistry; Oct 2023; URL https://doi.org/10.1021/acs.biochem.3c00293) clarified a key upstream step: ArnD is the deformylase that converts a formylated intermediate (C55P-Ara4FN) into the functional donor for ArnE/ArnF flipping and ArnT transfer (munozescudero2023structureandfunction pages 1-2, munozescudero2023structureandfunction pages 2-4). This strengthens the pathway’s mechanistic completeness: ArnF’s substrate (C55P-Ara4N) depends on ArnD function.
The same work provides quantitative/functional and structural insights: deletion of arnD causes accumulation of C55P-Ara4FN (and polymyxin sensitivity in the described genetic background), and purified ArnD efficiently deformylates C55P-Ara4FN in vitro in the presence of divalent metals (munozescudero2023structureandfunction pages 2-4).
Baijal et al. (PLOS Biology; Mar 2024; URL https://doi.org/10.1371/journal.pbio.3002558) connected envelope remodeling (Ara4N and pEtN lipid A modification) to stress physiology:
- In starvation conditions, polyphosphate kinase (PPK) is required for proper induction of BasRS (also known in related contexts as PmrAB-like signaling), which controls transcription/production of Arn-pathway proteins and EptA (baijal2024polyphosphatekinaseregulates pages 1-2, baijal2024polyphosphatekinaseregulates pages 8-9).
- The authors report 92 proteins significantly differentially expressed between wild-type and Δppk during starvation, with Arn/EptA downregulated, and Δppk cells lacking L-Ara4N and pEtN lipid A modifications under the tested conditions (baijal2024polyphosphatekinaseregulates pages 1-2).
Although this study does not re-measure ArnF flipping directly, it is a recent authoritative source that reaffirms the mechanistic placement of ArnE/ArnF as the flipping step for Und-P–Ara4N, upstream of ArnT (baijal2024polyphosphatekinaseregulates pages 3-5).
Ara4N lipid A modification is a well-established mechanism contributing to polymyxin resistance. ArnF is therefore indirectly a potential sensitization target: disrupting ArnF function prevents Ara4N modification and increases polymyxin susceptibility (yan2007anundecaprenylphosphateaminoarabinose pages 7-8).
Baijal et al. further propose that targeting PPK could sensitize bacteria to polymyxins by preventing proper BasRS-driven induction of Arn/EptA modifications during starvation (baijal2024polyphosphatekinaseregulates pages 1-2). This constitutes a practical, mechanism-based intervention concept that leverages the Arn pathway.
The strongest evidence is from genetics + lipid chemistry + membrane accessibility in E. coli:
- Donor present (biosynthesis intact) but periplasmic accessibility reduced and Ara4N-lipid A absent, which is the signature expected for a transbilayer transport defect rather than an enzymatic synthesis defect (yan2007anundecaprenylphosphateaminoarabinose pages 1-2, yan2007anundecaprenylphosphateaminoarabinose pages 7-8).
- The paired requirement for ArnE and ArnF supports a multi-component transport system rather than a single transporter (yan2007anundecaprenylphosphateaminoarabinose pages 1-2, yan2007anundecaprenylphosphateaminoarabinose pages 7-8).
Within the retrieved literature, ArnF is functionally assigned and topologically predicted, but a high-resolution structure of ArnF/ArnE or a reconstituted in vitro flipping assay for ArnF itself was not present in the retrieved 2023–2024 sources. Thus, mechanistic details such as proton coupling, exact stoichiometry, and residue-level substrate recognition remain inferential in this evidence set (yan2007anundecaprenylphosphateaminoarabinose pages 5-7).
| Functional Annotation | Evidence Type | Key Quantitative Findings & Observations | Source | Citation |
|---|---|---|---|---|
| Function: Subunit of heterodimeric flippase (ArnE/ArnF) translocating Und-P-L-Ara4N from cytoplasm to periplasm | Biochemical / Genetic: Sulfo-NHS-biotin labeling of spheroplasts; Null mutants ($pmrM$) | 4–5-fold reduction in periplasmic labeling of Und-P-Ara4N in mutants (MS peak area ratio 0.013 vs 0.069 in parent). Total cellular donor levels unchanged. | Yan et al. (2007) JBC | (yan2007anundecaprenylphosphateaminoarabinose pages 1-2, yan2007anundecaprenylphosphateaminoarabinose pages 2-4, yan2007anundecaprenylphosphateaminoarabinose media 80f295c9) |
| Phenotype: Essential for Polymyxin (Colistin) Resistance | Phenotypic Assay: Growth on polymyxin plates | Mutants sensitive to 15 µg/ml polymyxin (phenotype switched from resistant to sensitive). | Yan et al. (2007) JBC | (yan2007anundecaprenylphosphateaminoarabinose pages 1-2, yan2007anundecaprenylphosphateaminoarabinose pages 7-8) |
| Pathway Outcome: Modification of Lipid A with L-Ara4N | Mass Spectrometry: Lipid A profile analysis | >95% loss of L-Ara4N-modified lipid A species in $arnF$ ($pmrM$) mutants compared to parent. | Yan et al. (2007) JBC | (yan2007anundecaprenylphosphateaminoarabinose pages 7-8) |
| Regulation: Controlled by Polyphosphate Kinase (PPK) via BasRS two-component system during starvation | Proteomics / Western Blot: Differential expression in $\Delta ppk$ vs WT | 92 proteins differentially expressed; Arn proteins (including Arn-3Flag) significantly downregulated in $\Delta ppk$; loss of L-Ara4N lipid A peaks. | Baijal et al. (2024) PLOS Bio | (baijal2024polyphosphatekinaseregulates pages 3-5, baijal2024polyphosphatekinaseregulates pages 9-11, baijal2024polyphosphatekinaseregulates pages 1-2) |
| Upstream Context: Substrate production requires ArnD deformylase | Structural / Biochemical: Crystal structure & enzymatic assay | Deletion of $arnD$ accumulates formylated intermediate (C55P-Ara4FN), preventing ArnE/F transport; purified ArnD confirms deformylase activity. | Muñoz-Escudero et al. (2023) Biochemistry | (munozescudero2023structureandfunction pages 1-2, munozescudero2023structureandfunction pages 2-4) |
| Downstream Context: Substrate utilizated by ArnT glycosyltransferase | Genetic / Review: Pathway reconstruction | ArnT transfers L-Ara4N from the flipped undecaprenyl donor to Lipid A at the periplasmic face; ArnT topology confirms periplasmic active site. | Tavares-Carreón et al. (2016) Glycobiology | (tavarescarreon2016arntproteinsthat pages 2-3, moran2017theroleof pages 44-49) |
Table: This table aggregates key experimental evidence defining the role of ArnF as a lipid-linked oligosaccharide flippase subunit, including quantitative mass spectrometry data and recent regulatory insights.
References
(yan2007anundecaprenylphosphateaminoarabinose pages 1-2): Aixin Yan, Ziqiang Guan, and Christian R.H. Raetz. An undecaprenyl phosphate-aminoarabinose flippase required for polymyxin resistance in escherichia coli*. Journal of Biological Chemistry, 282:36077-36089, Dec 2007. URL: https://doi.org/10.1074/jbc.m706172200, doi:10.1074/jbc.m706172200. This article has 200 citations and is from a domain leading peer-reviewed journal.
(yan2007anundecaprenylphosphateaminoarabinose pages 5-7): Aixin Yan, Ziqiang Guan, and Christian R.H. Raetz. An undecaprenyl phosphate-aminoarabinose flippase required for polymyxin resistance in escherichia coli*. Journal of Biological Chemistry, 282:36077-36089, Dec 2007. URL: https://doi.org/10.1074/jbc.m706172200, doi:10.1074/jbc.m706172200. This article has 200 citations and is from a domain leading peer-reviewed journal.
(yan2007anundecaprenylphosphateaminoarabinose pages 2-4): Aixin Yan, Ziqiang Guan, and Christian R.H. Raetz. An undecaprenyl phosphate-aminoarabinose flippase required for polymyxin resistance in escherichia coli*. Journal of Biological Chemistry, 282:36077-36089, Dec 2007. URL: https://doi.org/10.1074/jbc.m706172200, doi:10.1074/jbc.m706172200. This article has 200 citations and is from a domain leading peer-reviewed journal.
(yan2007anundecaprenylphosphateaminoarabinose media 73fe93bb): Aixin Yan, Ziqiang Guan, and Christian R.H. Raetz. An undecaprenyl phosphate-aminoarabinose flippase required for polymyxin resistance in escherichia coli*. Journal of Biological Chemistry, 282:36077-36089, Dec 2007. URL: https://doi.org/10.1074/jbc.m706172200, doi:10.1074/jbc.m706172200. This article has 200 citations and is from a domain leading peer-reviewed journal.
(baijal2024polyphosphatekinaseregulates pages 3-5): Kanchi Baijal, Iryna Abramchuk, Carmen M. Herrera, Thien-Fah Mah, M. Stephen Trent, Mathieu Lavallée-Adam, and Michael Downey. Polyphosphate kinase regulates lps structure and polymyxin resistance during starvation in e. coli. PLOS Biology, 22:e3002558, Mar 2024. URL: https://doi.org/10.1371/journal.pbio.3002558, doi:10.1371/journal.pbio.3002558. This article has 6 citations and is from a highest quality peer-reviewed journal.
(baijal2024polyphosphatekinaseregulates pages 1-2): Kanchi Baijal, Iryna Abramchuk, Carmen M. Herrera, Thien-Fah Mah, M. Stephen Trent, Mathieu Lavallée-Adam, and Michael Downey. Polyphosphate kinase regulates lps structure and polymyxin resistance during starvation in e. coli. PLOS Biology, 22:e3002558, Mar 2024. URL: https://doi.org/10.1371/journal.pbio.3002558, doi:10.1371/journal.pbio.3002558. This article has 6 citations and is from a highest quality peer-reviewed journal.
(munozescudero2023structureandfunction pages 1-2): Daniel Muñoz-Escudero, Steven D. Breazeale, Myeongseon Lee, Ziqiang Guan, Christian R. H. Raetz, and Marcelo C. Sousa. Structure and function of arnd. a deformylase essential for lipid a modification with 4-amino-4-deoxy-l-arabinose and polymyxin resistance. Biochemistry, 62:2970-2981, Oct 2023. URL: https://doi.org/10.1021/acs.biochem.3c00293, doi:10.1021/acs.biochem.3c00293. This article has 8 citations and is from a peer-reviewed journal.
(tavarescarreon2016arntproteinsthat pages 2-3): Faviola Tavares-Carreón, Yasmine Fathy Mohamed, Angel Andrade, and Miguel A Valvano. Arnt proteins that catalyze the glycosylation of lipopolysaccharide share common features with bacterialn-oligosaccharyltransferases. Glycobiology, pages cwv095, Oct 2016. URL: https://doi.org/10.1093/glycob/cwv095, doi:10.1093/glycob/cwv095. This article has 27 citations and is from a peer-reviewed journal.
(yan2007anundecaprenylphosphateaminoarabinose media 80f295c9): Aixin Yan, Ziqiang Guan, and Christian R.H. Raetz. An undecaprenyl phosphate-aminoarabinose flippase required for polymyxin resistance in escherichia coli*. Journal of Biological Chemistry, 282:36077-36089, Dec 2007. URL: https://doi.org/10.1074/jbc.m706172200, doi:10.1074/jbc.m706172200. This article has 200 citations and is from a domain leading peer-reviewed journal.
(yan2007anundecaprenylphosphateaminoarabinose pages 7-8): Aixin Yan, Ziqiang Guan, and Christian R.H. Raetz. An undecaprenyl phosphate-aminoarabinose flippase required for polymyxin resistance in escherichia coli*. Journal of Biological Chemistry, 282:36077-36089, Dec 2007. URL: https://doi.org/10.1074/jbc.m706172200, doi:10.1074/jbc.m706172200. This article has 200 citations and is from a domain leading peer-reviewed journal.
(munozescudero2023structureandfunction pages 2-4): Daniel Muñoz-Escudero, Steven D. Breazeale, Myeongseon Lee, Ziqiang Guan, Christian R. H. Raetz, and Marcelo C. Sousa. Structure and function of arnd. a deformylase essential for lipid a modification with 4-amino-4-deoxy-l-arabinose and polymyxin resistance. Biochemistry, 62:2970-2981, Oct 2023. URL: https://doi.org/10.1021/acs.biochem.3c00293, doi:10.1021/acs.biochem.3c00293. This article has 8 citations and is from a peer-reviewed journal.
(baijal2024polyphosphatekinaseregulates pages 8-9): Kanchi Baijal, Iryna Abramchuk, Carmen M. Herrera, Thien-Fah Mah, M. Stephen Trent, Mathieu Lavallée-Adam, and Michael Downey. Polyphosphate kinase regulates lps structure and polymyxin resistance during starvation in e. coli. PLOS Biology, 22:e3002558, Mar 2024. URL: https://doi.org/10.1371/journal.pbio.3002558, doi:10.1371/journal.pbio.3002558. This article has 6 citations and is from a highest quality peer-reviewed journal.
(baijal2024polyphosphatekinaseregulates pages 9-11): Kanchi Baijal, Iryna Abramchuk, Carmen M. Herrera, Thien-Fah Mah, M. Stephen Trent, Mathieu Lavallée-Adam, and Michael Downey. Polyphosphate kinase regulates lps structure and polymyxin resistance during starvation in e. coli. PLOS Biology, 22:e3002558, Mar 2024. URL: https://doi.org/10.1371/journal.pbio.3002558, doi:10.1371/journal.pbio.3002558. This article has 6 citations and is from a highest quality peer-reviewed journal.
(moran2017theroleof pages 44-49): C Moran. The role of lipid a head group modification in escherichia coli virulence and polymyxin resistance. Unknown journal, 2017.
ArnF is one subunit of an undecaprenyl phosphate-alpha-L-Ara4N flippase heterodimer (ArnE/ArnF). This flippase translocates 4-amino-4-deoxy-L-arabinose-phosphoundecaprenol (alpha-L-Ara4N-phosphoundecaprenol) from the cytoplasmic to the periplasmic side of the inner membrane PMID:17928292.
This flipping step is essential for the L-Ara4N modification of lipid A by ArnT (whose active site faces the periplasm), which in turn is required for polymyxin resistance PMID:17928292.
ArnF operates in the L-Ara4N lipid A modification pathway:
1. UDP-glucose → UDP-glucuronic acid (Ugd)
2. UDP-glucuronic acid → UDP-4-ketopentose (ArnA C-terminal domain)
3. UDP-4-ketopentose → UDP-beta-L-Ara4N (ArnB, transamination)
4. UDP-beta-L-Ara4N → N-formylated form (ArnA N-terminal domain)
5. N-formyl-L-Ara4N → undecaprenyl-phosphate-L-Ara4N (ArnC, transfer to carrier lipid)
6. Deformylation (ArnD)
7. Flipping of undecaprenyl-phosphate-L-Ara4N across inner membrane (ArnE/ArnF) ← arnF acts here
8. Transfer of L-Ara4N to lipid A on periplasmic face (ArnT)
The GO:0140303 branch reveals an important ontology gap for ArnF:
GO:0140303 intramembrane lipid transporter activity
"Enables the transport of a lipid from a region of a membrane
to a different region on the same membrane."
├── GO:0017128 phospholipid scramblase activity
│ (ATP-independent, non-selective, bidirectional)
└── GO:0140326 ATPase-coupled intramembrane lipid transporter activity
"Catalysis of the movement of lipids from one membrane leaflet
to the other, driven by ATP hydrolysis."
├── GO:0140327 flippase activity
│ (exoplasmic → cytosolic, ATP-dependent)
│ ├── GO:0015247 aminophospholipid flippase activity
│ ├── GO:0140333 glycerophospholipid flippase activity
│ ├── GO:0140345 phosphatidylcholine flippase activity
│ ├── GO:0140351 glycosylceramide flippase activity
│ └── GO:0140347 N-retinylidene-PE flippase activity
└── GO:0140328 floppase activity
(cytosolic → exoplasmic, ATP-dependent)
├── GO:0015161 lipid III floppase activity (ECA assembly)
├── GO:0015437 lipopolysaccharide floppase activity
├── GO:0034202 glycolipid floppase activity
├── GO:0046623 sphingolipid floppase activity
└── GO:0090554 phosphatidylcholine floppase activity
ArnE/ArnF flips undecaprenyl phosphate-α-L-Ara4N from cytosolic → periplasmic leaflet.
This is the floppase direction (cytosolic → exoplasmic). However:
Conclusion: GO:0140303 is the only term that correctly captures ArnF's function without
making false claims about energy coupling. All children either require ATP or don't match
the directionality/selectivity.
There is no GO term for "ATP-independent, directional intramembrane lipid transporter
activity" — the space between scramblase (non-selective, bidirectional) and
flippase/floppase (ATP-dependent, directional). ArnE/ArnF falls in this gap: it is
directional and substrate-specific, but not ATP-coupled.
This could be flagged as a potential new term request: something like
"energy-independent intramembrane lipid transporter activity" or
"non-ATPase floppase activity" under GO:0140303.
The closest existing term by analogy is GO:0015161 (lipid III floppase activity) which
also handles undecaprenyl-linked substrates flipped across the bacterial inner membrane
during cell surface polysaccharide assembly — but for ECA rather than L-Ara4N lipid A
modification, and classified as ATP-dependent.
The IBA annotation to GO:0022857 (transmembrane transporter activity) was inferred from:
| Protein | Gene | Function | Mechanism |
|---|---|---|---|
| P23895 | emrE | Multidrug efflux pump | Transmembrane export (H+ antiport) |
| P69210 | mdtI | Spermidine export | Transmembrane export |
| P69212 | mdtJ | Spermidine export | Transmembrane export |
| P69937 | gdx (sugE) | Guanidinium export | Transmembrane export |
| P9WGF1 | mmr (Rv3065) | M. tuberculosis multidrug resistance | Transmembrane export |
| Q47377 | arnE | L-Ara4N flippase subunit | Intramembrane flip |
| P76474 | arnF | L-Ara4N flippase subunit | Intramembrane flip |
All non-ArnE/ArnF members are genuine solute exporters — they move substrates from
cytoplasm across the membrane to the periplasm/exterior. ArnE/ArnF does something
fundamentally different: it flips a lipid-linked substrate between membrane leaflets.
The PANTHER family PTHR30561 groups these by shared SMR/DMT fold (4-TM helices), but the
functional annotation "transmembrane transporter activity" correctly describes only the
exporters, not the flippase pair.
From PTHR30561-entries.csv, the family contains at least these subfamilies:
- SF9: ArnF-related (4-amino-4-deoxy-L-arabinose-phosphoundecaprenol flippase subunit)
- SF23: ArnE-related
- SF6: MdtI (spermidine export)
- SF2: MdtJ (spermidine export)
- Family-level (not assigned to SF): EmrE, Gdx/SugE
This means the IBA could in principle be refined at the subfamily level — SF9/SF23
should get intramembrane lipid transporter annotations, while SF2/SF6 and family-level
members keep transmembrane transporter annotations.
Note on SF9 subfamily mapping inconsistency: One entry in PTHR30561-entries.csv
(A8FRQ9, Shewanella sediminis ArnE) is named as ArnE but assigned to SF9
(ARNF-RELATED) rather than SF23 (ARNE-RELATED). This is likely a genuine PANTHER
classification based on sequence similarity — the Shewanella ArnE ortholog may be
more similar to ArnF sequences. This does not affect the E. coli annotations or the
IBA analysis, since E. coli ArnE (Q47377) and ArnF (P76474) are correctly assigned
to SF23 and SF9 respectively.
EcoCyc contributed 5 of the 18 total GO annotations for arnF:
| Term | Evidence | Assessment |
|---|---|---|
| GO:0010041 response to iron(III) ion | IGI (PMID:12139617) | Over-annotated — conflates operon regulation with gene function |
| GO:0010041 response to iron(III) ion | IEP (PMID:15322361) | Over-annotated — expression pattern ≠ function |
| GO:1901264 carbohydrate derivative transport | IMP (PMID:17928292) | Good — supported by sulfo-NHS-biotin assay |
| GO:1901505 carbohydrate derivative transmembrane transporter activity | IMP (PMID:17928292) | Good — complementation + biotinylation evidence |
| GO:0005886 plasma membrane | IDA (PMID:15919996) | Good — GFP/PhoA topology study |
The iron response annotations are a textbook case of over-annotation: iron activates
BasS-BasR → induces arn operon → ArnF expressed. But ArnF doesn't sense, bind, or
detoxify iron. By this logic, every gene in an iron-responsive regulon would be annotated
to "response to iron(III) ion," which is clearly inappropriate.
The EcoCyc IMP annotations are well-supported and accurate. The IDA for plasma membrane
is the strongest CC evidence available.
id: P76474
gene_symbol: arnF
product_type: PROTEIN
status: DRAFT
taxon:
id: NCBITaxon:83333
label: Escherichia coli (strain K12)
description: ArnF (formerly PmrM/YfbJ) is a subunit of the undecaprenyl phosphate-alpha-L-Ara4N
flippase, forming a heterodimer with ArnE that translocates 4-amino-4-deoxy-L-arabinose-phosphoundecaprenol
(alpha-L-Ara4N-phosphoundecaprenol) from the cytoplasmic to the periplasmic side of
the inner membrane [PMID:17928292]. This flipping step is essential for L-Ara4N
modification of lipid A by ArnT (whose active site faces the periplasm), which confers
resistance to polymyxin and cationic antimicrobial peptides. ArnF is a 128 AA inner
membrane protein with 4 transmembrane helices, distantly related to EmrE and other
members of the DMT/SMR superfamily. It is part of the arnBCADTEF operon, regulated
by BasR in response to iron and other environmental stimuli [PMID:15569938].
existing_annotations:
# ============================================================
# IBA ANNOTATIONS (from phylogenetic inference, GO_REF:0000033)
# ============================================================
- term:
id: GO:0022857
label: transmembrane transporter activity
evidence_type: IBA
original_reference_id: GO_REF:0000033
review:
summary: ArnF is a subunit of the undecaprenyl phosphate-alpha-L-Ara4N flippase,
which translocates a lipid-linked sugar across the inner membrane [PMID:17928292].
This is technically an intramembrane lipid transporter (flipping a lipid-linked
substrate from one leaflet to the other), rather than a classical transmembrane
transporter that moves solutes across the membrane. The IBA annotation to the
parent term 'transmembrane transporter activity' captures the general transporter
function, which is phylogenetically sound given the SMR/DMT superfamily membership.
action: MODIFY
reason: While ArnF is part of the transporter superfamily (DMT/SMR) and the IBA
annotation is phylogenetically reasonable, 'transmembrane transporter activity'
(GO:0022857) is too generic and does not capture the specific intramembrane lipid
flipping function. The more accurate term is GO:0140303 'intramembrane lipid
transporter activity', which describes transport of a lipid from one region of
a membrane to a different region on the same membrane -- precisely the flippase
function demonstrated for ArnF [PMID:17928292].
proposed_replacement_terms:
- id: GO:0140303
label: intramembrane lipid transporter activity
supported_by:
- reference_id: PMID:17928292
supporting_text: PmrL and PmrM could specifically function to flip undecaprenyl
phosphate-alpha-L-Ara4N from the cytosolic to the periplasmic side of the
inner membrane, possibly functioning as a heterodimer
- term:
id: GO:0005886
label: plasma membrane
evidence_type: IBA
original_reference_id: GO_REF:0000033
review:
summary: ArnF is an inner membrane protein in E. coli. In GO, the E. coli inner
membrane (cytoplasmic membrane) is annotated as 'plasma membrane' (GO:0005886),
which is correct usage for bacteria. This is supported by experimental evidence
from topology analysis [PMID:15919996] and is consistent with its function as
a flippase in the inner membrane [PMID:17928292].
action: ACCEPT
reason: The IBA annotation to plasma membrane is correct. ArnF is an integral
inner membrane protein with 4 transmembrane helices, confirmed by global topology
analysis. In bacterial GO annotation, the inner/cytoplasmic membrane is properly
annotated as plasma membrane (GO:0005886).
supported_by:
- reference_id: PMID:15919996
supporting_text: Global topology analysis of the Escherichia coli inner membrane
proteome
- reference_id: PMID:17928292
supporting_text: PmrL and PmrM are small, hydrophobic, inner membrane proteins
with many of the characteristics of small multidrug resistance transporters.
Both PmrL and PmrM are predicted to have four membrane-spanning helices
- term:
id: GO:0055085
label: transmembrane transport
evidence_type: IBA
original_reference_id: GO_REF:0000033
review:
summary: ArnF participates in the translocation of undecaprenyl phosphate-alpha-L-Ara4N
across the inner membrane [PMID:17928292]. This is an intramembrane translocation
(flipping from one leaflet to the other) rather than a transmembrane transport
event in the classical sense of moving a solute from one aqueous compartment to
another. The IBA annotation captures the general transport process from the SMR
family phylogenetic context.
action: ACCEPT
reason: While the precise mechanism is intramembrane lipid flipping rather than
classical transmembrane transport of a solute, GO:0055085 'transmembrane transport'
is a reasonable process term for this function since the substrate does cross
the membrane bilayer. The IBA inference from the SMR/DMT family is phylogenetically
sound. The existing experimental IMP annotations to more specific terms
(GO:1901264 carbohydrate derivative transport) complement this broader annotation.
supported_by:
- reference_id: PMID:17928292
supporting_text: The data imply that both PmrL and PmrM are involved in the
translocation of undecaprenyl phosphate-alpha-LAra4N across the inner membrane
# ============================================================
# IEA ANNOTATIONS (automated electronic annotations)
# ============================================================
- term:
id: GO:0005886
label: plasma membrane
evidence_type: IEA
original_reference_id: GO_REF:0000120
review:
summary: Automated annotation to plasma membrane. ArnF is confirmed as an inner
membrane protein (equivalent to plasma membrane in bacteria) by both experimental
topology studies [PMID:15919996] and by its established function as a flippase
in the inner membrane [PMID:17928292].
action: ACCEPT
reason: This IEA annotation is correct and is independently supported by IDA
evidence (PMID:15919996) and IBA evidence (GO_REF:0000033). Duplicating the
more specific experimental annotation is acceptable for IEA.
supported_by:
- reference_id: PMID:15919996
supporting_text: Global topology analysis of the Escherichia coli inner membrane
proteome
- term:
id: GO:0006629
label: lipid metabolic process
evidence_type: IEA
original_reference_id: GO_REF:0000043
review:
summary: Automated annotation from UniProt keyword mapping. ArnF's primary function
is as a flippase for lipid-linked sugar substrates, participating in the L-Ara4N
lipid A modification pathway [PMID:17928292]. While ArnF is involved in the
overall pathway of lipid A modification, calling its specific function 'lipid
metabolic process' is very broad.
action: ACCEPT
reason: While this is a very broad term, it is not incorrect. ArnF participates
in a lipid metabolic pathway (lipid A modification) by translocating a lipid-linked
substrate. The UniProt keywords include 'Lipid biosynthesis' and 'Lipid metabolism'
which map to this term. More specific BP annotations (GO:0046493 lipid A
metabolic process, GO:0009245 lipid A biosynthetic process) are also present
and provide the necessary specificity. This IEA serves as a broader parent
annotation.
supported_by:
- reference_id: PMID:17928292
supporting_text: We propose that PmrL and PmrM be renamed ArnE and ArnF,
respectively (Fig. 2B), given their function in generating L-Ara4N modified
lipid A species
- term:
id: GO:0009103
label: lipopolysaccharide biosynthetic process
evidence_type: IEA
original_reference_id: GO_REF:0000120
review:
summary: Automated annotation to LPS biosynthesis. ArnF is part of the arn operon
which is involved in modifying lipid A (the lipid component of LPS) with L-Ara4N
[PMID:17928292]. UniProt explicitly lists this under PATHWAY as 'Bacterial outer
membrane biogenesis; lipopolysaccharide biosynthesis'.
action: ACCEPT
reason: ArnF functions in the L-Ara4N modification of lipid A, which is a component
of lipopolysaccharide. The LPS biosynthetic process term appropriately captures
the pathway context. This is consistent with the UniProt pathway annotation and
the established role of the arn operon in LPS modification.
supported_by:
- reference_id: PMID:17928292
supporting_text: Modification of lipid A with the 4-amino-4-deoxy-L-arabinose
(L-Ara4N) moiety is required for resistance to polymyxin and cationic
antimicrobial peptides in Escherichia coli and Salmonella typhimurium
- term:
id: GO:0009245
label: lipid A biosynthetic process
evidence_type: IEA
original_reference_id: GO_REF:0000120
review:
summary: Automated annotation to lipid A biosynthesis. ArnF participates in the
L-Ara4N modification of lipid A, which is a post-biosynthetic modification
rather than de novo lipid A biosynthesis [PMID:17928292]. The more precise term
would be GO:0046493 'lipid A metabolic process' (which is already annotated via
IMP), since ArnF is involved in modifying existing lipid A rather than
synthesizing it de novo.
action: ACCEPT
reason: While strictly speaking ArnF participates in lipid A modification rather
than de novo lipid A biosynthesis, the L-Ara4N modification pathway is
conventionally grouped under lipid A biosynthesis in the broader sense of
generating the final modified lipid A species. UniProt keywords include
'Lipid A biosynthesis', and this annotation is broadly consistent. The IMP
annotation to GO:0046493 (lipid A metabolic process) provides a more accurate
complementary annotation.
supported_by:
- reference_id: PMID:17928292
supporting_text: In the pmrL or pmrM deletion mutants, over 95% of each of
the L-Ara4N-modified lipid A species was missing
- term:
id: GO:0016020
label: membrane
evidence_type: IEA
original_reference_id: GO_REF:0000002
review:
summary: InterPro-based annotation to the generic 'membrane' component. ArnF is
an integral membrane protein with 4 transmembrane helices located in the inner
(plasma) membrane. This is correct but much less specific than the plasma
membrane annotations already present.
action: ACCEPT
reason: This is a correct but very broad cellular component annotation. ArnF is
unquestionably a membrane protein (4 TM helices, integral inner membrane protein).
While GO:0005886 (plasma membrane) is more informative and is already annotated
via IBA, IDA, and IEA, keeping this broader IEA annotation is acceptable as it
provides the InterPro-derived evidence.
supported_by:
- reference_id: PMID:17928292
supporting_text: A BLASTp analysis of PmrL and PmrM shows that both are small
integral membrane proteins with four putative trans-membrane helices
- term:
id: GO:0022857
label: transmembrane transporter activity
evidence_type: IEA
original_reference_id: GO_REF:0000120
review:
summary: Automated annotation to transmembrane transporter activity. ArnF is a
subunit of the undecaprenyl phosphate-alpha-L-Ara4N flippase [PMID:17928292],
which functions as an intramembrane lipid transporter rather than a classical
transmembrane transporter. This IEA parallels the IBA annotation to the same
term.
action: MODIFY
reason: This IEA annotation to GO:0022857 is the same term as the IBA annotation.
As with the IBA, 'transmembrane transporter activity' is too generic for ArnF's
specific intramembrane lipid flipping function. The more accurate term is
GO:0140303 'intramembrane lipid transporter activity', which precisely describes
the flippase function demonstrated for ArnF [PMID:17928292].
proposed_replacement_terms:
- id: GO:0140303
label: intramembrane lipid transporter activity
supported_by:
- reference_id: PMID:17928292
supporting_text: PmrL and PmrM could specifically function to flip undecaprenyl
phosphate-alpha-L-Ara4N from the cytosolic to the periplasmic side of the
inner membrane, possibly functioning as a heterodimer
- term:
id: GO:0055085
label: transmembrane transport
evidence_type: IEA
original_reference_id: GO_REF:0000104
review:
summary: Automated annotation to transmembrane transport, transferred from manual
annotations on related proteins via shared sequence features. This parallels the
IBA annotation to the same BP term and is broadly consistent with ArnF's role in
translocating undecaprenyl phosphate-alpha-L-Ara4N across the inner membrane
[PMID:17928292].
action: ACCEPT
reason: This IEA annotation is consistent with the IBA annotation to the same
term and is supported by the experimental evidence for ArnF's flippase function.
As an automated annotation it provides an acceptable broader process term.
supported_by:
- reference_id: PMID:17928292
supporting_text: The data imply that both PmrL and PmrM are involved in the
translocation of undecaprenyl phosphate-alpha-LAra4N across the inner membrane
- term:
id: GO:1901505
label: carbohydrate derivative transmembrane transporter activity
evidence_type: IEA
original_reference_id: GO_REF:0000002
review:
summary: InterPro-based annotation to carbohydrate derivative transmembrane
transporter activity. The substrate of ArnF is undecaprenyl phosphate-alpha-L-Ara4N,
which contains L-Ara4N (4-amino-4-deoxy-L-arabinose), a carbohydrate derivative.
This term is more specific than generic transmembrane transporter activity and
captures the carbohydrate-linked nature of the substrate [PMID:17928292].
action: ACCEPT
reason: This annotation is accurate -- the substrate translocated by the ArnE/ArnF
flippase is undecaprenyl phosphate-alpha-L-Ara4N, which is a carbohydrate
derivative (containing L-Ara4N, a modified arabinose). This is more informative
than the generic 'transmembrane transporter activity' and is consistent with the
IMP annotation to the same term from PMID:17928292.
supported_by:
- reference_id: PMID:17928292
supporting_text: PmrL and PmrM could specifically function to flip undecaprenyl
phosphate-alpha-L-Ara4N from the cytosolic to the periplasmic side of the
inner membrane
# ============================================================
# EXPERIMENTAL ANNOTATIONS
# ============================================================
- term:
id: GO:0046493
label: lipid A metabolic process
evidence_type: IMP
original_reference_id: PMID:17928292
review:
summary: In-frame deletion of arnF (pmrM) in a pmrAc background results in loss
of over 95% of L-Ara4N-modified lipid A species, demonstrating that ArnF is
required for lipid A modification [PMID:17928292]. The mutant phenotype (loss
of lipid A modification, polymyxin sensitivity) directly implicates ArnF in the
lipid A metabolic process.
action: ACCEPT
reason: This IMP annotation is well-supported by the deletion phenotype data in
Yan et al. 2007. The arnF deletion mutant lacks L-Ara4N modified lipid A,
demonstrating a clear role in lipid A metabolism. This is a core process
annotation for ArnF.
supported_by:
- reference_id: PMID:17928292
supporting_text: In the pmrL or pmrM deletion mutants, over 95% of each of
the L-Ara4N-modified lipid A species was missing
- reference_id: PMID:17928292
supporting_text: the pmrL and the pmrM deletion mutants (as well as the double
deletion mutant) were sensitive to 15 μg/ml polymyxin
- term:
id: GO:0010041
label: response to iron(III) ion
evidence_type: IGI
original_reference_id: PMID:12139617
review:
summary: This annotation is based on Chamnongpol et al. 2002 which studied
Fe(III)-mediated toxicity and the PmrA/PmrB system. The study showed that the
PmrA/PmrB system (which regulates the arn operon including arnF) is important
for Fe(III) resistance. However, arnF's connection to iron response is indirect
-- iron activates BasS/BasR (PmrA/PmrB homolog), which induces the arn operon,
leading to lipid A modification. ArnF itself does not sense or directly respond
to iron; it is merely transcriptionally induced as part of a regulon. The IGI
evidence code suggests genetic interaction, but the gene's role is downstream
in the effector pathway rather than in iron sensing or response per se.
action: MARK_AS_OVER_ANNOTATED
reason: The 'response to iron(III) ion' annotation conflates transcriptional
regulation with gene function. ArnF is a lipid flippase whose expression
happens to be induced by iron via the BasS-BasR two-component system. The gene
does not directly sense, bind, or respond to iron. Many genes in stress-induced
regulons would receive inappropriate 'response to X' annotations if mere
transcriptional induction were sufficient. The PMID:12139617 study focused on
PmrA/PmrB-dependent Fe(III) resistance mechanisms but did not specifically
demonstrate a direct role for arnF in iron response. The connection is via
operon co-regulation, not direct function.
supported_by:
- reference_id: PMID:12139617
supporting_text: Fe(III) exerts its microbicidal activity by a mechanism that
is oxygen independent and different from that mediated by Fe(II)
- reference_id: PMID:15322361
supporting_text: the BasS-BasR system is essential for this iron-dependent
induction of yfbE
- term:
id: GO:1901264
label: carbohydrate derivative transport
evidence_type: IMP
original_reference_id: PMID:17928292
review:
summary: The arnF deletion mutant shows 4-5 fold reduced accessibility of
undecaprenyl phosphate-alpha-L-Ara4N to membrane-impermeable sulfo-NHS-biotin
labeling, while total levels of the substrate are unchanged [PMID:17928292].
This demonstrates that ArnF is required for transport of this carbohydrate
derivative (L-Ara4N-linked lipid) across the inner membrane. The substrate
undecaprenyl phosphate-alpha-L-Ara4N contains L-Ara4N (a carbohydrate
derivative), making this term appropriate.
action: ACCEPT
reason: This IMP annotation accurately describes the biological process. The
sulfo-NHS-biotin accessibility assay in Yan et al. 2007 provides direct evidence
that ArnF is involved in transporting the carbohydrate derivative undecaprenyl
phosphate-alpha-L-Ara4N across the membrane. This is a core process for ArnF.
supported_by:
- reference_id: PMID:17928292
supporting_text: At the 4-h time point, there was a 4-5-fold reduction in ratio
of the monoisotopic peak areas for biotinylated undecaprenyl
phosphate-alpha-L-Ara4N compared with unmodified undecaprenyl
phosphate-alpha-L-Ara4N
- reference_id: PMID:17928292
supporting_text: undecaprenyl phosphate-alpha-L-Ara4N levels were the same or
slightly higher in the mutants than in the parent, indicating that appropriate
amounts of the prenol lipid donor of the L-Ara4N moiety are still synthesized
in these mutants
- term:
id: GO:1901505
label: carbohydrate derivative transmembrane transporter activity
evidence_type: IMP
original_reference_id: PMID:17928292
review:
summary: Experimental evidence from the sulfo-NHS-biotin accessibility assay
demonstrates that ArnF is required for translocating undecaprenyl
phosphate-alpha-L-Ara4N (a carbohydrate derivative) across the inner membrane
[PMID:17928292]. The arnF mutant shows reduced periplasmic accessibility of the
substrate while total levels remain unchanged, consistent with impaired
transporter function. Complementation with pWSK29-PmrM restores polymyxin
resistance, confirming the specific role of ArnF [PMID:17928292].
action: ACCEPT
reason: This MF annotation is well-supported by the experimental data in Yan et
al. 2007. The sulfo-NHS-biotin assay demonstrates transporter activity for
a carbohydrate derivative substrate. The complementation experiment confirms
gene-specific function. This represents a core molecular function of ArnF.
supported_by:
- reference_id: PMID:17928292
supporting_text: The data imply that both PmrL and PmrM are involved in the
translocation of undecaprenyl phosphate-alpha-LAra4N across the inner membrane
- reference_id: PMID:17928292
supporting_text: polymyxin resistance was recovered in the pmrM deletion mutant
AY101 by transforming with pWSK29-PmrM
- term:
id: GO:0005886
label: plasma membrane
evidence_type: IDA
original_reference_id: PMID:15919996
review:
summary: Daley et al. 2005 performed a global topology analysis of the E. coli
inner membrane proteome using C-terminal GFP/PhoA fusions. ArnF (YfbJ) was
among the 601 inner membrane proteins characterized, with C-terminal tagging
establishing its inner membrane localization [PMID:15919996]. In bacterial GO
annotation, the inner membrane is annotated as plasma membrane (GO:0005886).
action: ACCEPT
reason: This IDA annotation is based on direct experimental evidence from GFP/PhoA
topology analysis. The C-terminal fusion approach provides reliable evidence for
inner membrane localization. This is the strongest evidence for the cellular
component annotation and represents a core localization for ArnF.
supported_by:
- reference_id: PMID:15919996
supporting_text: Using C-terminal tagging with the alkaline phosphatase and
green fluorescent protein, we established the periplasmic or cytoplasmic
locations of the C termini for 601 inner membrane proteins
- term:
id: GO:0010041
label: response to iron(III) ion
evidence_type: IEP
original_reference_id: PMID:15322361
review:
summary: Hagiwara et al. 2004 used genome-wide transcriptome profiling to show
that the yfbE operon (now arn operon, including arnF) is induced in response to
external iron via the BasS-BasR two-component system [PMID:15322361]. The IEP
evidence code (Inferred from Expression Pattern) is technically appropriate for
a gene whose expression changes in response to iron. However, as with the IGI
annotation above, this annotation conflates transcriptional regulation with
direct functional involvement in iron response. ArnF's function is lipid
flipping, not iron sensing.
action: MARK_AS_OVER_ANNOTATED
reason: The IEP evidence code is technically appropriate -- arnF expression is
induced by iron via the BasS-BasR system. However, annotating a gene to
'response to iron(III) ion' based solely on transcriptional induction
conflates regulation with function. ArnF is a flippase that translocates
undecaprenyl phosphate-alpha-L-Ara4N; it does not participate in iron sensing,
binding, or detoxification. Many genes in iron-responsive regulons (e.g.,
house-keeping genes in Fur regulon) would be similarly over-annotated. The
annotation is not wrong in the strict GO sense (the protein is produced in
response to iron), but it does not represent a core function and is misleading
about ArnF's actual role.
supported_by:
- reference_id: PMID:15322361
supporting_text: the BasS-BasR system is essential for this iron-dependent
induction of yfbE
- reference_id: PMID:15322361
supporting_text: the hypothetical yfbE operon that appears to be implicated
in the modification of lipopolysaccharides is regulated at the level of
transcription in response to external iron
# ============================================================
# NEW ANNOTATIONS (suggested additions not in existing set)
# ============================================================
- term:
id: GO:0140303
label: intramembrane lipid transporter activity
evidence_type: IMP
original_reference_id: PMID:17928292
review:
summary: ArnF functions as a subunit of a flippase that translocates undecaprenyl
phosphate-alpha-L-Ara4N from the cytoplasmic to the periplasmic leaflet of the
inner membrane [PMID:17928292]. This is specifically an intramembrane lipid
transport event -- the lipid-linked substrate is moved from one leaflet to the
other within the same membrane, not transported across the membrane into
solution. GO:0140303 (intramembrane lipid transporter activity) precisely
captures this function.
action: NEW
reason: This term is more specific and accurate for ArnF's molecular function
than the existing GO:0022857 (transmembrane transporter activity) or GO:1901505
(carbohydrate derivative transmembrane transporter activity). The sulfo-NHS-biotin
accessibility assay in Yan et al. 2007 directly demonstrates that ArnF is
required for moving undecaprenyl phosphate-alpha-L-Ara4N to the periplasmic face
of the inner membrane -- an intramembrane lipid translocation event. This
should be considered a core MF annotation for ArnF.
supported_by:
- reference_id: PMID:17928292
supporting_text: PmrL and PmrM could specifically function to flip undecaprenyl
phosphate-alpha-L-Ara4N from the cytosolic to the periplasmic side of the
inner membrane, possibly functioning as a heterodimer
- reference_id: PMID:17928292
supporting_text: At the 4-h time point, there was a 4-5-fold reduction in ratio
of the monoisotopic peak areas for biotinylated undecaprenyl
phosphate-alpha-L-Ara4N compared with unmodified undecaprenyl
phosphate-alpha-L-Ara4N
- reference_id: file:ECOLI/arnF/arnF-deep-research-falcon.md
supporting_text: ArnE/ArnF are placed as the flipping step between donor synthesis
(ArnB/C/A/D) and transfer to lipid A (ArnT) in the L-Ara4N modification pathway
core_functions:
- description: Intramembrane flippase activity for undecaprenyl phosphate-alpha-L-Ara4N,
translocating this lipid-linked sugar from the cytoplasmic to periplasmic leaflet
of the inner membrane as a heterodimer with ArnE
molecular_function:
id: GO:0140303
label: intramembrane lipid transporter activity
supported_by:
- reference_id: PMID:17928292
supporting_text: PmrL and PmrM could specifically function to flip undecaprenyl
phosphate-alpha-L-Ara4N from the cytosolic to the periplasmic side of the inner
membrane, possibly functioning as a heterodimer
- reference_id: file:ECOLI/arnF/arnF-deep-research-falcon.md
supporting_text: ArnE/ArnF are placed as the flipping step between donor synthesis
(ArnB/C/A/D) and transfer to lipid A (ArnT) in the L-Ara4N modification pathway
directly_involved_in:
- id: GO:0046493
label: lipid A metabolic process
- id: GO:1901264
label: carbohydrate derivative transport
- id: GO:0009103
label: lipopolysaccharide biosynthetic process
locations:
- id: GO:0005886
label: plasma membrane
proposed_new_terms:
- proposed_name: ATP-independent intramembrane lipid transporter activity
proposed_definition: Enables the directional transport of a lipid from one leaflet
of a membrane to the other leaflet, without coupling to ATP hydrolysis. Unlike
scramblases, the transport is directional and substrate-specific.
justification: The current GO hierarchy under GO:0140303 (intramembrane lipid
transporter activity) has two children -- ATPase-coupled intramembrane lipid
transporter activity (GO:0140326, parent of flippase/floppase) and phospholipid
scramblase activity (GO:0017128, ATP-independent but non-selective/bidirectional).
ArnE/ArnF and possibly other bacterial undecaprenyl-linked sugar flippases are
directional and substrate-specific but not ATP-dependent, falling in a gap between
these two branches. GO:0015161 (lipid III floppase activity) is the closest
analog but is classified as ATP-dependent under floppase activity.
proposed_parent:
id: GO:0140303
label: intramembrane lipid transporter activity
supported_by:
- reference_id: PMID:17928292
supporting_text: PmrL and PmrM could specifically function to flip undecaprenyl
phosphate-alpha-L-Ara4N from the cytosolic to the periplasmic side of the inner
membrane, possibly functioning as a heterodimer
references:
- id: GO_REF:0000002
title: Gene Ontology annotation through association of InterPro records with GO
terms
findings: []
- id: GO_REF:0000033
title: Annotation inferences using phylogenetic trees
findings: []
- id: GO_REF:0000043
title: Gene Ontology annotation based on UniProtKB/Swiss-Prot keyword mapping
findings: []
- id: GO_REF:0000104
title: Electronic Gene Ontology annotations created by transferring manual GO annotations
between related proteins based on shared sequence features
findings: []
- id: GO_REF:0000120
title: Combined Automated Annotation using Multiple IEA Methods
findings: []
- id: PMID:12139617
title: Fe(III)-mediated cellular toxicity.
findings:
- statement: The PmrA/PmrB system is required for Fe(III) resistance in Salmonella
and E. coli
supporting_text: Fe(III) exhibits microbicidal activity towards strains of Salmonella
enterica, Escherichia coli and Klebsiella pneumoniae defective in the
Fe(III)-responding PmrA/PmrB signal transduction system
- id: PMID:15322361
title: A Genome-wide view of the Escherichia coli BasS-BasR two-component system
implicated in iron-responses.
findings:
- statement: The arn operon (yfbE operon) is induced by iron via the BasS-BasR
two-component system
supporting_text: the BasS-BasR system is essential for this iron-dependent
induction of yfbE
- id: PMID:15569938
title: Phenotypic differences between Salmonella and Escherichia coli resulting from
the disparate regulation of homologous genes.
findings:
- statement: The arn operon is induced by BasR (PmrA) in E. coli in response to Fe(3+)
supporting_text: E. coli K-12 induces PmrA-activated gene transcription and
polymyxin B resistance in response to Fe(3+), but that it is blind to the
low Mg(2+) signal
- id: PMID:15919996
title: Global topology analysis of the Escherichia coli inner membrane proteome.
findings:
- statement: ArnF (YfbJ) inner membrane localization confirmed by C-terminal
GFP/PhoA fusion topology analysis
supporting_text: Using C-terminal tagging with the alkaline phosphatase and green
fluorescent protein, we established the periplasmic or cytoplasmic locations
of the C termini for 601 inner membrane proteins
- id: PMID:17928292
title: An undecaprenyl phosphate-aminoarabinose flippase required for polymyxin
resistance in Escherichia coli.
findings:
- statement: ArnF (PmrM) deletion causes polymyxin sensitivity and loss of L-Ara4N
modification of lipid A
supporting_text: the pmrL and the pmrM deletion mutants (as well as the double
deletion mutant) were sensitive to 15 μg/ml polymyxin
- statement: Over 95% of L-Ara4N-modified lipid A species are lost in the arnF
mutant
supporting_text: In the pmrL or pmrM deletion mutants, over 95% of each of the
L-Ara4N-modified lipid A species was missing
- statement: ArnF is required for flipping undecaprenyl phosphate-alpha-L-Ara4N
to the periplasmic face of the inner membrane
supporting_text: PmrL and PmrM could specifically function to flip undecaprenyl
phosphate-alpha-L-Ara4N from the cytosolic to the periplasmic side of the inner
membrane, possibly functioning as a heterodimer
- statement: Sulfo-NHS-biotin labeling demonstrates 4-5 fold reduced periplasmic
accessibility of substrate in arnF mutant
supporting_text: At the 4-h time point, there was a 4-5-fold reduction in ratio
of the monoisotopic peak areas for biotinylated undecaprenyl
phosphate-alpha-L-Ara4N compared with unmodified undecaprenyl
phosphate-alpha-L-Ara4N
- statement: ArnF is indispensable and cannot be complemented by ArnE alone
supporting_text: polymyxin resistance was recovered in the pmrM deletion mutant
AY101 by transforming with pWSK29-PmrM
- id: file:ECOLI/arnF/arnF-deep-research-falcon.md
title: Deep research summary for arnF (Falcon/Edison Scientific Literature)
findings:
- statement: ArnE/ArnF are placed as the flipping step between donor synthesis
(ArnB/C/A/D) and transfer to lipid A (ArnT) in the L-Ara4N modification pathway
- statement: ArnD is the deformylase that produces the ArnE/ArnF substrate (C55P-Ara4N)
from C55P-Ara4FN, confirmed by Munoz-Escudero et al. 2023
- statement: Polyphosphate kinase (PPK) regulates Arn pathway expression via
BasRS during starvation (Baijal et al. 2024)