This protein contains TWO completely unrelated functional domains:
Soluble enzyme, chloroplast stroma localized in plants
ARV1 domain (C-terminal, ~aa 480-719)
STRONG EVIDENCE: The same organism has separate, properly-sized genes for both domains:
- NCGR_LOCUS4558 (A0A811MHP4): Histidinol dehydrogenase, chloroplastic (478 aa) - normal HDH
- NCGR_LOCUS4557 (A0A811MIX4): Protein ARV (230 aa) - normal ARV1
Note that LOCUS4557 and LOCUS4558 are sequential/adjacent loci, strongly suggesting the
gene predictor incorrectly merged two adjacent genes in a different genomic region.
Biological incompatibility: HDH is a soluble chloroplast stroma enzyme; ARV1 is an ER
membrane protein with transmembrane domains. A single protein cannot function in both
compartments simultaneously. The N-terminal transit peptide (for chloroplast import) would
prevent ER membrane insertion, and conversely the transmembrane domains would interfere
with chloroplast import.
Genome quality: The M. lutarioriparius genome is derived from WGS preliminary data
(noted in UniProt CAUTION field). The sequence originated from CAJGYO010000002.
Plant histidinol dehydrogenase catalyzes the final step of histidine biosynthesis:
L-histidinol + 2 NAD+ + H2O -> L-histidine + 2 NADH + 3 H+
ARV1 family proteins mediate sterol homeostasis:
- ER membrane-localized with 2+ transmembrane helices
- Involved in sterol transport from ER to plasma membrane
- Contains Arv1 homology domain (AHD) with cysteine-rich zinc-binding motif
- Arabidopsis has two ARV isoforms (AtArv1p, AtArv2p), both ER-localized PMID:16725371
- Loss of ARV1 causes altered sterol distribution, sphingolipid metabolism changes
- Regulates sphingolipid metabolism
All GO annotations on this entry reflect the conflation of two separate gene products:
- HDH-related annotations (GO:0004399, GO:0000105, GO:0051287, GO:0046872, GO:0009570, GO:0005829) come from the HDH domain
- ARV1-related annotations (GO:0032366, GO:0097036, GO:0006665, GO:0016125, GO:0005789, GO:0005783, GO:0016020) come from the ARV1 domain
- Some annotations (GO:0005737, GO:0016491, GO:0016616, GO:0009507) could apply to either
The correct approach would be to split the annotations by domain, but since this is a
single UniProt entry, the review should note that annotations are domain-specific and
that this appears to be a gene model error.
All 17 original assertions reviewed and preserved. The previous universal over-annotation judgment depended on an unproved gene-model error and exclusive localization. See the reproducible bioinformatics RESULTS.md: chromosome-1 adjacency is real (1,050 bases), but the candidate is on chromosome 2; HDH has 460/472 aligned identities and retains E368/H369 plus Q300/H303/D402/H461. The missing-residue warning belongs to ARV rule RU368065. Restored six HDH-function/pathway rows plus broad cytoplasm and membrane; nine ARV/compartment rows remain UNDECIDED pending focused adjudication. No NEW rows. Removed unsupported core sterol-binding assertion.
PMID:16725371 abstract explicitly reports that removal of the cysteine-rich ARV subdomain has no effect on activity; this prevents treating divergent cysteines as proof of loss. Its ER experiment concerns GFP-tagged Arabidopsis homologs in onion cells, not the Miscanthus fusion. Historical manual research is retained but marked DISPUTED. Exact source coordinates, sequence alignments, raw records and limitations are in the bioinformatics folder.
Corrected local-file quotations or matched supporting text to its claim where applicable. Missing-assay caveats remain in reasons rather than serving as positive support. Annotation actions are unchanged.
Verified GO_REF titles against https://geneontology.org/GO_REF/0000104, https://geneontology.org/GO_REF/0000117 and https://geneontology.org/GO_REF/0000120: UniRule feature-based transfer, ARBA models and combined automated methods, respectively.
Removed limitation/tool-access statements from positive support where applicable and retained the actual lineage or sequence evidence. Historical uncertainties remain in the rationale rather than being treated as proof of function.
Assessed NCGR_LOCUS10166-hypotheses/fusion-model-arv-function-and-targeting/openscientist.md.
The report supports the prior HDH-positive interpretation and adds the missing ARV scope
check: PMID:23668914 directly found ER-plasma membrane sterol transport intact in yeast
arv1 mutants, while ARV1 loss alters cortical ER organization and plasma membrane lipid
homeostasis. This resolves GO:0032366 as an over-specific ARV-family propagation
rather than a merely unresolved row. GO:0097036, sphingolipid/sterol metabolism and
ER/plastid targeting stay unresolved because the candidate still contains an ARV-like
region and the HDH-ARV transcript itself remains unverified.