Carnitine O-acetyltransferase (CAT2) is a mitochondrial and peroxisomal enzyme that catalyzes the reversible transfer of acetyl groups from acetyl-CoA to carnitine, forming acetylcarnitine. This shuttle reaction is critical for transporting activated acetyl groups across the impermeable inner mitochondrial and peroxisomal membranes. CAT2 exists as two isoforms derived from alternative initiation: the mitochondrial isoform (located at the inner mitochondrial membrane) and the peroxisomal isoform (located in the peroxisomal matrix). The enzyme plays a central role in carnitine-dependent metabolic processes and stress protection, particularly in response to oxidative stress. CAT2 is essential for fatty acid oxidation in peroxisomes and supports mitochondrial metabolism by facilitating acetyl-CoA transport.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
|
GO:0004092
carnitine O-acetyltransferase activity
|
IBA
GO_REF:0000033 |
ACCEPT |
Summary: Carnitine O-acetyltransferase activity is the primary and well-established enzymatic function of CAT2. This is supported by phylogenetic inference (IBA) from orthologous proteins and backed by direct experimental evidence (IMP from PMID:8420957). The UniProt record explicitly states the catalytic activity: (R)-carnitine + acetyl-CoA = O-acetyl-(R)-carnitine + CoA (EC 2.3.1.7). The term appropriately represents the core molecular function of this enzyme.
Supporting Evidence:
PMID:8420957
This cDNA was used successfully to disrupt the gene for the mitochondrial isoenzyme of CAT, which was shown by measuring the enzyme activity and by immunoblot [Establishes enzymatic activity]
|
|
GO:0005739
mitochondrion
|
IBA
GO_REF:0000033 |
ACCEPT |
Summary: CAT2 localizes to mitochondria, specifically as a mitochondrial isoform at the inner mitochondrial membrane. This is supported by phylogenetic inference (IBA) and confirmed by direct experimental evidence (IDA from PMID:18427809 and PMID:25372298). The UniProt record explicitly documents the mitochondrial localization of the primary isoform.
Supporting Evidence:
PMID:18427809
Carnitine and carnitine acetyltransferases in the yeast Saccharomyces cerevisiae: a role for carnitine in stress protection. [Documents mitochondrial localization of CAT2]
|
|
GO:0005777
peroxisome
|
IBA
GO_REF:0000033 |
ACCEPT |
Summary: CAT2 localizes to peroxisomes as a second isoform derived from alternative initiation. This is supported by phylogenetic inference (IBA) and confirmed by direct experimental evidence (IDA from PMID:18427809, PMID:22375831). The UniProt record documents that the peroxisomal isoform is produced by alternative initiation at Met-23 and contains a C-terminal peroxisomal targeting signal (SKL).
Supporting Evidence:
PMID:18427809
Carnitine and carnitine acetyltransferases in the yeast Saccharomyces cerevisiae: a role for carnitine in stress protection. [Documents peroxisomal localization of CAT2]
|
|
GO:0009437
carnitine metabolic process
|
IBA
GO_REF:0000033 |
ACCEPT |
Summary: CAT2 is essential for carnitine-dependent metabolic processes. This is supported by phylogenetic inference (IBA) and strong experimental evidence (IMP from PMID:11329169). The enzyme catalyzes the reversible acetylation of carnitine, which is the central reaction in the carnitine shuttle for transferring acetyl groups across organellar membranes.
Supporting Evidence:
PMID:11329169
Carnitine-dependent metabolic activities in Saccharomyces cerevisiae: three carnitine acetyltransferases are essential in a carnitine-dependent strain [Establishes CAT2 role in carnitine metabolism]
|
|
GO:0004092
carnitine O-acetyltransferase activity
|
IEA
GO_REF:0000120 |
ACCEPT |
Summary: This is a computational annotation from combined automated annotation methods (IEA from GO_REF:0000120). It represents the same core function as the IBA and IMP annotations, supported by EC classification 2.3.1.7 and RHEA reaction mapping. This annotation is redundant with the higher-quality IBA and IMP evidence but provides additional confirmation of the enzymatic function.
|
|
GO:0005743
mitochondrial inner membrane
|
IEA
GO_REF:0000044 |
ACCEPT |
Summary: This annotation specifies the precise mitochondrial localization of CAT2 (mitochondrial isoform). This is a computational annotation derived from UniProtKB subcellular location vocabulary mapping (GO_REF:0000044) and is accurate. The UniProt record explicitly states the primary isoform localizes to the mitochondrial inner membrane as a peripheral membrane protein. The term is appropriately specific and supported by the documented isoform structure.
|
|
GO:0005777
peroxisome
|
IEA
GO_REF:0000044 |
ACCEPT |
Summary: This is a computational annotation from UniProtKB subcellular location vocabulary mapping (GO_REF:0000044) documenting the peroxisomal localization of the CAT2 peroxisomal isoform. This is accurate and supported by direct experimental evidence (IDA from PMID:18427809, PMID:22375831). The annotation appropriately represents the documented alternative isoform.
|
|
GO:0006629
lipid metabolic process
|
IEA
GO_REF:0000043 |
KEEP AS NON CORE |
Summary: This annotation is derived from UniProtKB keyword mapping (GO_REF:0000043, KW-0443: Lipid metabolism). CAT2 is involved in lipid metabolism through its role in the carnitine shuttle for fatty acid oxidation in peroxisomes. However, this is an indirect and broad annotation. While not incorrect, the more specific process term "carnitine-dependent fatty acid oxidation" or "fatty acid metabolic process" would be more informative.
Reason: This term is accurate but overly general. CAT2 contributes to lipid metabolism through the carnitine shuttle facilitating fatty acid oxidation, but this is a secondary effect of its primary function. The term represents a higher-level process that encompasses the more specific functions already captured by GO:0006631 (fatty acid metabolic process) and GO:0009437 (carnitine metabolic process).
|
|
GO:0006631
fatty acid metabolic process
|
IEA
GO_REF:0000043 |
ACCEPT |
Summary: This annotation is derived from UniProtKB keyword mapping (GO_REF:0000043, KW-0276: Fatty acid metabolism). CAT2 is directly involved in fatty acid oxidation through the carnitine shuttle mechanism. In yeast, peroxisomes are the primary site of fatty acid oxidation, and CAT2 is essential for this process by facilitating the transport of acetyl groups from peroxisomes to mitochondria. This is supported by PMID:11329169, which documents the essential role of all three CAT enzymes in carnitine-dependent fatty acid metabolism.
Supporting Evidence:
PMID:11329169
L-carnitine and all three CATs are essential for growth on non-fermentable carbon sources in a strain with a disrupted CIT2 gene [Documents CAT2 role in fatty acid metabolism]
|
|
GO:0016740
transferase activity
|
IEA
GO_REF:0000043 |
KEEP AS NON CORE |
Summary: This annotation is derived from UniProtKB keyword mapping (GO_REF:0000043, KW-0808: Transferase). CAT2 is indeed a transferase, catalyzing the transfer of acetyl groups from acetyl-CoA to carnitine. However, this is a very broad and general molecular function term. The specific function is much better represented by GO:0004092 (carnitine O-acetyltransferase activity) and GO:0016746 (acyltransferase activity), which provide more informative classification.
Reason: While technically correct, this term is too general and uninformative. GO:0004092 provides the specific enzymatic classification, and this broader term adds little additional value. It represents a parent term of the more specific acyltransferase activity.
|
|
GO:0016746
acyltransferase activity
|
IEA
GO_REF:0000120 |
ACCEPT |
Summary: This annotation is derived from automated annotation methods (GO_REF:0000120) mapping InterPro domain IPR000542 (Carnitine/choline acetyltransferase family). CAT2 is indeed an acyltransferase, specifically catalyzing the transfer of an acetyl group (an acyl group) from acetyl-CoA to carnitine. This is a reasonable intermediate-level classification between the general transferase activity and the specific carnitine O-acetyltransferase activity.
|
|
GO:0005515
protein binding
|
IPI
PMID:27107014 An inter-species protein-protein interaction network across ... |
MARK AS OVER ANNOTATED |
Summary: This annotation is from a protein-protein interaction study (IPI, PMID:27107014), documenting interaction with a human ortholog (UniProtKB:Q9H190). While this indicates CAT2 has protein binding capability, the term "protein binding" is non-specific and uninformative. Every protein binds to other molecules; this does not distinguish the biological function. Without knowledge of the specific interaction partner or functional consequence, this annotation provides minimal functional insight.
Reason: The term "protein binding" is too vague and generic. This annotation documents a protein-protein interaction from an inter-species study, but provides no functional context. The interaction partner appears to be a human ortholog used for comparative analysis rather than a specific yeast interaction. More informative would be specific binding partner information or functional roles (e.g., substrate/product binding). This annotation does not represent a core biological function of the enzyme.
Supporting Evidence:
PMID:27107014
An inter-species protein-protein interaction network across vast evolutionary distance.
|
|
GO:0005777
peroxisome
|
IDA
PMID:22375831 Identification of core components and transient interactors ... |
ACCEPT |
Summary: This annotation documents peroxisomal localization based on direct evidence (IDA). PMID:22375831 is a proteomics study of the peroxisomal importomer that identified CAT2 as a component or interactor in peroxisomal protein import machinery. This provides direct evidence for peroxisomal localization. The annotation is accurate and supported by the experimental approach.
Supporting Evidence:
PMID:22375831
Identification of core components and transient interactors of the peroxisomal importomer by dual-track stable isotope labeling with amino acids in cell culture analysis [Direct identification in peroxisomal protein import studies]
|
|
GO:0005739
mitochondrion
|
HDA
PMID:24769239 Quantitative variations of the mitochondrial proteome and ph... |
ACCEPT |
Summary: This annotation documents mitochondrial localization based on homologous annotation (HDA). PMID:24769239 is a quantitative proteomics study of the mitochondrial proteome that identified CAT2. This provides evidence for mitochondrial localization through detection of the protein in mitochondrial preparations. The annotation is accurate and represents core localization information.
Supporting Evidence:
PMID:24769239
2014 Apr 24. Quantitative variations of the mitochondrial proteome and phosphoproteome during fermentative and respiratory growth in Saccharomyces cerevisiae.
|
|
GO:0005739
mitochondrion
|
HDA
PMID:14576278 The proteome of Saccharomyces cerevisiae mitochondria. |
ACCEPT |
Summary: This annotation documents mitochondrial localization based on homologous annotation (HDA). PMID:14576278 is a proteomics study of the Saccharomyces cerevisiae mitochondrial proteome, providing evidence for CAT2 identification in mitochondrial preparations. This corroborates the mitochondrial localization annotation.
Supporting Evidence:
PMID:14576278
The proteome of Saccharomyces cerevisiae mitochondria.
|
|
GO:0005739
mitochondrion
|
HDA
PMID:16823961 Toward the complete yeast mitochondrial proteome: multidimen... |
ACCEPT |
Summary: This annotation documents mitochondrial localization based on homologous annotation (HDA). PMID:16823961 is a multidimensional proteomics study toward the complete yeast mitochondrial proteome, providing another line of proteomic evidence for CAT2 identification in mitochondrial preparations. This further corroborates the mitochondrial localization.
Supporting Evidence:
PMID:16823961
Toward the complete yeast mitochondrial proteome: multidimensional separation techniques for mitochondrial proteomics.
|
|
GO:0004092
carnitine O-acetyltransferase activity
|
IMP
PMID:8420957 Cloning and sequencing of a cDNA encoding Saccharomyces cere... |
ACCEPT |
Summary: This annotation documents carnitine O-acetyltransferase activity based on direct experimental evidence (IMP - Inferred from Mutant Phenotype). PMID:8420957 is the original cloning paper that established CAT2 identity through gene disruption studies and enzyme activity measurements. This is the highest-quality evidence for the enzymatic function. The disruption phenotype (decreased acetylcarnitine content and altered pyruvate metabolism) directly demonstrates the catalytic activity of CAT2.
Supporting Evidence:
PMID:8420957
The acetylcarnitine content of these cells decreased significantly. A search in the PIR protein data base revealed that besides the known carnitine acyltransferases, choline acyltransferases are highly homologous to yeast CAT [Establishes CAT2 enzymatic function]
|
|
GO:0005739
mitochondrion
|
IDA
PMID:18427809 Carnitine and carnitine acetyltransferases in the yeast Sacc... |
ACCEPT |
Summary: This annotation documents mitochondrial localization based on direct experimental evidence (IDA). PMID:18427809 is a functional study of carnitine acetyltransferases in yeast that documents CAT2 localization and function in stress protection. The direct identification provides evidence for the mitochondrial localization of the primary isoform. This is high-quality evidence for the subcellular localization.
Supporting Evidence:
PMID:18427809
Carnitine and carnitine acetyltransferases in the yeast Saccharomyces cerevisiae: a role for carnitine in stress protection [Documents CAT2 localization]
|
|
GO:0005777
peroxisome
|
IDA
PMID:18427809 Carnitine and carnitine acetyltransferases in the yeast Sacc... |
ACCEPT |
Summary: This annotation documents peroxisomal localization based on direct experimental evidence (IDA). PMID:18427809 provides experimental evidence for the peroxisomal isoform of CAT2. The study demonstrates that CAT2 localizes to both mitochondria and peroxisomes, consistent with the documented alternative initiation products that generate two isoforms with different localizations.
Supporting Evidence:
PMID:18427809
Carnitine and carnitine acetyltransferases in the yeast Saccharomyces cerevisiae: a role for carnitine in stress protection [Demonstrates CAT2 localization to both compartments]
|
|
GO:0009437
carnitine metabolic process
|
IMP
PMID:11329169 Carnitine-dependent metabolic activities in Saccharomyces ce... |
ACCEPT |
Summary: This annotation documents carnitine metabolic process involvement based on direct experimental evidence (IMP - Inferred from Mutant Phenotype). PMID:11329169 is a comprehensive study of carnitine-dependent metabolic activities that demonstrates CAT2 is one of three essential carnitine acetyltransferases. The mutant selection strategy and complementation analysis provide strong genetic evidence for CAT2 involvement in carnitine metabolism.
Supporting Evidence:
PMID:11329169
L-carnitine is required for the transfer of activated acyl-groups across intracellular membranes in eukaryotic organisms. In Saccharomyces cerevisiae, peroxisomal membranes are impermeable to acetyl-CoA [Essential role in carnitine-dependent metabolism]
|
Exported on March 22, 2026 at 03:15 AM
Organism: Saccharomyces cerevisiae
Sequence:
MRICHSRTLSNLKDLPITSRRAMHSAIVNYSTQKAQFPVETNNGEHYWAEKPNKFYQNKRPNFQGITFAKQQDLPSLPVPELKSTLDKYLQTIRPFCNDVETFERQQLLCKDFSEHMGPILQDRLKEYANDKRNWMAKFWDEQSYLQYNDPIVPYVSYFYSHMPLPNHLSKIDNDPLIKATAIISTVVKFIEAIKDESLPVEIIKGMPFCMNSFSLMFNTSRLPGKPEDNQDTNIFYSVYENNFVTIAYKGKFYKLMTHDGNDKPLSENEIWRQLYSVVFQGSQSDPKLGGIGSLTSLPRDQWREVHLELMKDPISQDSLETIHKSSFMLCLDLDQSPVTLEEKSRNCWHGDGINRFYDKSLQFLVTGNGSSGFLAEHSKMDGTPTLFLNNYVCQQLNKLDVDDFMRKVITPSSTVAMKPMELPFIITPKIHKAIESAQLQFKETIGEHDLRVWHYNKYGKTFIKRHGMSPDAFIQQVIQLAVFKYLKRQLPTYEAASTRKYFKGRTETGRSVSTASLEFVSKWQNGDVPIAEKIQALKHSAKEHSTYLKNAANGNGVDRHFFGLKNMLKSNDDQIPPLFKDPLFNYSSTWLISTSQLSSEYFDGYGWSQVNDNGFGLAYMLNNEWLHINIVNKPAKSGASVNRLHYYLSQAADEIFDALENENKRKAKL
I begin with the InterPro architecture. The sequence core from residues 65–658 is assigned to IPR000542 (Acyltransferase ChoActase/COT/CPT family), establishing membership in the choline/carnitine O-acyltransferase enzyme family that catalyzes acyl transfer between CoA thioesters and quaternary ammonium alcohol acceptors. This family signature is embedded within IPR023213 (Chloramphenicol acetyltransferase-like domain superfamily, residues 74–655), a structural superfamily whose alpha/beta scaffold supports acyltransfer chemistry. Within this framework, IPR039551 (Choline/Carnitine o-acyltransferase, domain 1 and 2, residues 77–650) resolves the enzyme into the canonical two-domain catalytic assembly characteristic of carnitine/choline acyltransferases, while IPR042231 (Choline/Carnitine o-acyltransferase, domain 2 homologous superfamily, residues 134–452) defines the second catalytic lobe that completes the active-site cleft. The ordered layout—an N-terminal family-defining region leading into tandem catalytic domains—creates the bilobal cavity that binds CoA thioesters and positions a quaternary ammonium substrate for acyl transfer.
This architecture dictates molecular function: the ChoActase/COT/CPT family catalyzes reversible acyl transfer between acyl-CoA and carnitine/choline. The bilobal domain 1–2 arrangement and CAT-like superfamily scaffold produce a catalytic center that stabilizes the acyl-enzyme intermediate and aligns CoA and quaternary ammonium alcohol for O-acyl transfer. Thus, the primary molecular function is acyltransferase chemistry formalized as GO:0016746 acyltransferase activity.
From function to process, acyltransferases of this class manage intracellular acyl flux, particularly in pathways that buffer and redistribute acyl groups. In yeast, this chemistry supports lipid and acyl-group handling rather than direct fatty acid catabolism. Consequently, the activity feeds into acyl-group and lipid management pathways, aligning with GO:0006807 as the overarching cellular biosynthetic/transcriptional framework that encompasses these acyl-metabolic routes.
The cellular component can be inferred from the soluble, bilobal enzyme architecture and absence of transmembrane features in the domain layout. CAT-like acyltransferases of this family typically operate as soluble enzymes associated with cytosolic metabolic hubs. Therefore, I infer a cytosolic localization corresponding to GO:0005737 as the cellular label for the compartmental context.
Mechanistically, I hypothesize that the enzyme forms a soluble acyltransferase that channels acyl groups between CoA and quaternary ammonium alcohol acceptors. In yeast lipid metabolism, this role would interface with enzymes that generate and consume acyl-CoA pools. I therefore anticipate transient assemblies with acyl-CoA synthetases that load acyl groups onto CoA, and with downstream acyltransferases that route acyl flux toward storage or remodeling. Likely partners include enzymes that maintain acyl-CoA homeostasis and acyl-group shuttling systems; these assemblies would position the enzyme as a dynamic node coordinating acyl transfer within the cytosol.
A soluble acyltransferase in baker’s yeast that uses a bilobal catalytic architecture to transfer acyl groups between CoA thioesters and quaternary ammonium alcohol acceptors. By assembling a two-domain active site typical of carnitine/choline acyltransferases, it supports intracellular acyl flux and lipid handling in the cytosol, likely buffering and redistributing acyl groups among metabolic pathways through reversible acyl transfer chemistry.
Probable acyltransferase.
IPR000542, family) — residues 65-658IPR023213, homologous_superfamily) — residues 74-655IPR039551, domain) — residues 77-650IPR042231, homologous_superfamily) — residues 134-452Molecular Function: molecular_function (GO:0003674), catalytic activity (GO:0003824), transferase activity (GO:0016740), acyltransferase activity (GO:0016746), acyltransferase activity, transferring groups other than amino-acyl groups (GO:0016747), O-acyltransferase activity (GO:0008374), acetyltransferase activity (GO:0016407), carnitine O-acyltransferase activity (GO:0016406), O-acetyltransferase activity (GO:0016413)
Biological Process: biological_process (GO:0008150), metabolic process (GO:0008152), cellular process (GO:0009987), cellular metabolic process (GO:0044237), nitrogen compound metabolic process (GO:0006807), organic substance metabolic process (GO:0071704), cellular nitrogen compound metabolic process (GO:0034641), cellular modified amino acid metabolic process (GO:0006575), organonitrogen compound metabolic process (GO:1901564), amino-acid betaine metabolic process (GO:0006577), carnitine metabolic process (GO:0009437)
Cellular Component: cellular_component (GO:0005575), cellular anatomical entity (GO:0110165), intracellular anatomical structure (GO:0005622), organelle (GO:0043226), - Function and Localization Inference: (GO:0005737), microbody (GO:0042579), mitochondrion (GO:0005739), intracellular organelle (GO:0043229), membrane-bounded organelle (GO:0043227), intracellular membrane-bounded organelle (GO:0043231), peroxisome (GO:0005777)
Generated by BioReason
Exported on March 22, 2026 at 03:15 AM
Organism: Saccharomyces cerevisiae
Sequence:
MRICHSRTLSNLKDLPITSRRAMHSAIVNYSTQKAQFPVETNNGEHYWAEKPNKFYQNKRPNFQGITFAKQQDLPSLPVPELKSTLDKYLQTIRPFCNDVETFERQQLLCKDFSEHMGPILQDRLKEYANDKRNWMAKFWDEQSYLQYNDPIVPYVSYFYSHMPLPNHLSKIDNDPLIKATAIISTVVKFIEAIKDESLPVEIIKGMPFCMNSFSLMFNTSRLPGKPEDNQDTNIFYSVYENNFVTIAYKGKFYKLMTHDGNDKPLSENEIWRQLYSVVFQGSQSDPKLGGIGSLTSLPRDQWREVHLELMKDPISQDSLETIHKSSFMLCLDLDQSPVTLEEKSRNCWHGDGINRFYDKSLQFLVTGNGSSGFLAEHSKMDGTPTLFLNNYVCQQLNKLDVDDFMRKVITPSSTVAMKPMELPFIITPKIHKAIESAQLQFKETIGEHDLRVWHYNKYGKTFIKRHGMSPDAFIQQVIQLAVFKYLKRQLPTYEAASTRKYFKGRTETGRSVSTASLEFVSKWQNGDVPIAEKIQALKHSAKEHSTYLKNAANGNGVDRHFFGLKNMLKSNDDQIPPLFKDPLFNYSSTWLISTSQLSSEYFDGYGWSQVNDNGFGLAYMLNNEWLHINIVNKPAKSGASVNRLHYYLSQAADEIFDALENENKRKAKL
I begin with the InterPro architecture. The sequence core from residues 65–658 is assigned to IPR000542 (Acyltransferase ChoActase/COT/CPT family), establishing membership in the choline/carnitine O-acyltransferase enzyme family that catalyzes acyl transfer between CoA thioesters and quaternary ammonium alcohol acceptors. This family signature is embedded within IPR023213 (Chloramphenicol acetyltransferase-like domain superfamily, residues 74–655), a structural superfamily whose alpha/beta scaffold supports acyltransfer chemistry. Within this framework, IPR039551 (Choline/Carnitine o-acyltransferase, domain 1 and 2, residues 77–650) resolves the enzyme into the canonical two-domain catalytic assembly characteristic of carnitine/choline acyltransferases, while IPR042231 (Choline/Carnitine o-acyltransferase, domain 2 homologous superfamily, residues 134–452) defines the second catalytic lobe that completes the active-site cleft. The ordered layout—an N-terminal family-defining region leading into tandem catalytic domains—creates the bilobal cavity that binds CoA thioesters and positions a quaternary ammonium substrate for acyl transfer.
This architecture dictates molecular function: the ChoActase/COT/CPT family catalyzes reversible acyl transfer between acyl-CoA and carnitine/choline. The bilobal domain 1–2 arrangement and CAT-like superfamily scaffold produce a catalytic center that stabilizes the acyl-enzyme intermediate and aligns CoA and quaternary ammonium alcohol for O-acyl transfer. Thus, the primary molecular function is acyltransferase chemistry formalized as GO:0016746 acyltransferase activity.
From function to process, acyltransferases of this class manage intracellular acyl flux, particularly in pathways that buffer and redistribute acyl groups. In yeast, this chemistry supports lipid and acyl-group handling rather than direct fatty acid catabolism. Consequently, the activity feeds into acyl-group and lipid management pathways, aligning with GO:0006807 as the overarching cellular biosynthetic/transcriptional framework that encompasses these acyl-metabolic routes.
The cellular component can be inferred from the soluble, bilobal enzyme architecture and absence of transmembrane features in the domain layout. CAT-like acyltransferases of this family typically operate as soluble enzymes associated with cytosolic metabolic hubs. Therefore, I infer a cytosolic localization corresponding to GO:0005737 as the cellular label for the compartmental context.
Mechanistically, I hypothesize that the enzyme forms a soluble acyltransferase that channels acyl groups between CoA and quaternary ammonium alcohol acceptors. In yeast lipid metabolism, this role would interface with enzymes that generate and consume acyl-CoA pools. I therefore anticipate transient assemblies with acyl-CoA synthetases that load acyl groups onto CoA, and with downstream acyltransferases that route acyl flux toward storage or remodeling. Likely partners include enzymes that maintain acyl-CoA homeostasis and acyl-group shuttling systems; these assemblies would position the enzyme as a dynamic node coordinating acyl transfer within the cytosol.
A soluble acyltransferase in baker’s yeast that uses a bilobal catalytic architecture to transfer acyl groups between CoA thioesters and quaternary ammonium alcohol acceptors. By assembling a two-domain active site typical of carnitine/choline acyltransferases, it supports intracellular acyl flux and lipid handling in the cytosol, likely buffering and redistributing acyl groups among metabolic pathways through reversible acyl transfer chemistry.
Probable acyltransferase.
IPR000542, family) — residues 65-658IPR023213, homologous_superfamily) — residues 74-655IPR039551, domain) — residues 77-650IPR042231, homologous_superfamily) — residues 134-452Molecular Function: molecular_function (GO:0003674), catalytic activity (GO:0003824), transferase activity (GO:0016740), acyltransferase activity (GO:0016746), acyltransferase activity, transferring groups other than amino-acyl groups (GO:0016747), O-acyltransferase activity (GO:0008374), acetyltransferase activity (GO:0016407), carnitine O-acyltransferase activity (GO:0016406), O-acetyltransferase activity (GO:0016413)
Biological Process: biological_process (GO:0008150), metabolic process (GO:0008152), cellular process (GO:0009987), cellular metabolic process (GO:0044237), nitrogen compound metabolic process (GO:0006807), organic substance metabolic process (GO:0071704), cellular nitrogen compound metabolic process (GO:0034641), cellular modified amino acid metabolic process (GO:0006575), organonitrogen compound metabolic process (GO:1901564), amino-acid betaine metabolic process (GO:0006577), carnitine metabolic process (GO:0009437)
Cellular Component: cellular_component (GO:0005575), cellular anatomical entity (GO:0110165), intracellular anatomical structure (GO:0005622), organelle (GO:0043226), - Function and Localization Inference: (GO:0005737), microbody (GO:0042579), mitochondrion (GO:0005739), intracellular organelle (GO:0043229), membrane-bounded organelle (GO:0043227), intracellular membrane-bounded organelle (GO:0043231), peroxisome (GO:0005777)
Generated by BioReason
Source: CAT2-deep-research-bioreason-rl.md
The BioReason summary states:
A soluble acyltransferase in baker's yeast that uses a bilobal catalytic architecture to transfer acyl groups between CoA thioesters and quaternary ammonium alcohol acceptors.
This correctly identifies the enzyme as an acyltransferase in the carnitine/choline family, and the description of the catalytic chemistry is broadly accurate. However, the summary never specifies that CAT2 is a carnitine O-acetyltransferase (GO:0004092, EC 2.3.1.7), which is the well-established core function. The phrase "quaternary ammonium alcohol acceptors" is technically inclusive of carnitine but needlessly vague for a protein whose substrate specificity is well characterized.
By assembling a two-domain active site typical of carnitine/choline acyltransferases, it supports intracellular acyl flux and lipid handling in the cytosol, likely buffering and redistributing acyl groups among metabolic pathways through reversible acyl transfer chemistry.
The claim that CAT2 operates "in the cytosol" is incorrect. The curated review documents that CAT2 localizes to mitochondria (inner membrane, peripheral) and peroxisomes, producing two isoforms via alternative translation initiation. Multiple IDA and HDA annotations confirm mitochondrial and peroxisomal localization (PMID:18427809, PMID:22375831, PMID:24769239). The cytosolic localization claim appears to be an erroneous inference from "soluble" architecture and lack of transmembrane domain detection.
The biological process description is vague -- "intracellular acyl flux and lipid handling" -- whereas the curated review specifies the carnitine shuttle for transferring acetyl groups across organellar membranes and the role in fatty acid oxidation (GO:0006631) and carnitine metabolic process (GO:0009437). The carnitine shuttle function is the defining biological role.
The functional summary completely misses: the dual isoform biology (mitochondrial vs. peroxisomal), the role in oxidative stress protection (PMID:18427809), and the essential role in growth on non-fermentable carbon sources.
Comparison with interpro2go:
The interpro2go annotation (GO_REF:0000120) correctly assigns acyltransferase activity (GO:0016746) based on IPR000542. BioReason's functional summary essentially paraphrases the interpro2go-level annotation -- identifying broad acyltransferase activity from the ChoActase/COT/CPT family domain -- without adding meaningful biological insight. In fact, the curated IMP evidence (PMID:8420957) pins the function more precisely to carnitine O-acetyltransferase activity (GO:0004092), which BioReason fails to reach. The localization error (cytosol instead of mitochondria/peroxisome) goes beyond interpro2go, which correctly includes GO:0005739 (mitochondrion) and GO:0005777 (peroxisome) in its CC predictions.
The thinking trace methodically walks through domain architecture and makes reasonable structural inferences. The error in localization stems from relying on "absence of transmembrane features" to infer cytosolic residence, ignoring that many organellar matrix/lumen proteins lack transmembrane domains. The trace does not appear to use any organism-specific or gene-specific knowledge beyond what InterPro provides.
id: P32796
gene_symbol: CAT2
aliases:
- CAT
- YCAT
- YML042W
- YM8054.01
product_type: PROTEIN
status: COMPLETE
taxon:
id: NCBITaxon:559292
label: Saccharomyces cerevisiae
description: 'Carnitine O-acetyltransferase (CAT2) is a mitochondrial and peroxisomal
enzyme that catalyzes the reversible transfer of acetyl groups from acetyl-CoA to
carnitine, forming acetylcarnitine. This shuttle reaction is critical for transporting
activated acetyl groups across the impermeable inner mitochondrial and peroxisomal
membranes. CAT2 exists as two isoforms derived from alternative initiation: the
mitochondrial isoform (located at the inner mitochondrial membrane) and the peroxisomal
isoform (located in the peroxisomal matrix). The enzyme plays a central role in
carnitine-dependent metabolic processes and stress protection, particularly in response
to oxidative stress. CAT2 is essential for fatty acid oxidation in peroxisomes and
supports mitochondrial metabolism by facilitating acetyl-CoA transport.'
core_functions:
- molecular_function:
id: GO:0004092
label: carnitine O-acetyltransferase activity
description: 'Primary enzymatic function. CAT2 catalyzes the reversible acetylation
of carnitine using acetyl-CoA as the acetyl donor (EC 2.3.1.7). This activity
is essential for the carnitine shuttle, which transfers activated acetyl groups
across organellar membranes.'
existing_annotations:
- term:
id: GO:0004092
label: carnitine O-acetyltransferase activity
evidence_type: IBA
original_reference_id: GO_REF:0000033
review:
summary: 'Carnitine O-acetyltransferase activity is the primary and well-established
enzymatic function of CAT2. This is supported by phylogenetic inference (IBA)
from orthologous proteins and backed by direct experimental evidence (IMP
from PMID:8420957). The UniProt record explicitly states the catalytic activity:
(R)-carnitine + acetyl-CoA = O-acetyl-(R)-carnitine + CoA (EC 2.3.1.7). The
term appropriately represents the core molecular function of this enzyme.'
action: ACCEPT
supported_by:
- reference_id: PMID:8420957
supporting_text: 'This cDNA was used successfully to disrupt the gene for
the mitochondrial isoenzyme of CAT, which was shown by measuring the enzyme
activity and by immunoblot [Establishes enzymatic activity]'
- term:
id: GO:0005739
label: mitochondrion
evidence_type: IBA
original_reference_id: GO_REF:0000033
review:
summary: 'CAT2 localizes to mitochondria, specifically as a mitochondrial isoform
at the inner mitochondrial membrane. This is supported by phylogenetic inference
(IBA) and confirmed by direct experimental evidence (IDA from PMID:18427809
and PMID:25372298). The UniProt record explicitly documents the mitochondrial
localization of the primary isoform.'
action: ACCEPT
supported_by:
- reference_id: PMID:18427809
supporting_text: 'Carnitine and carnitine acetyltransferases in the yeast
Saccharomyces cerevisiae: a role for carnitine in stress protection. [Documents
mitochondrial localization of CAT2]'
- term:
id: GO:0005777
label: peroxisome
evidence_type: IBA
original_reference_id: GO_REF:0000033
review:
summary: 'CAT2 localizes to peroxisomes as a second isoform derived from alternative
initiation. This is supported by phylogenetic inference (IBA) and confirmed
by direct experimental evidence (IDA from PMID:18427809, PMID:22375831). The
UniProt record documents that the peroxisomal isoform is produced by alternative
initiation at Met-23 and contains a C-terminal peroxisomal targeting signal
(SKL).'
action: ACCEPT
supported_by:
- reference_id: PMID:18427809
supporting_text: 'Carnitine and carnitine acetyltransferases in the yeast
Saccharomyces cerevisiae: a role for carnitine in stress protection. [Documents
peroxisomal localization of CAT2]'
- term:
id: GO:0009437
label: carnitine metabolic process
evidence_type: IBA
original_reference_id: GO_REF:0000033
review:
summary: 'CAT2 is essential for carnitine-dependent metabolic processes. This
is supported by phylogenetic inference (IBA) and strong experimental evidence
(IMP from PMID:11329169). The enzyme catalyzes the reversible acetylation
of carnitine, which is the central reaction in the carnitine shuttle for transferring
acetyl groups across organellar membranes.'
action: ACCEPT
supported_by:
- reference_id: PMID:11329169
supporting_text: 'Carnitine-dependent metabolic activities in Saccharomyces
cerevisiae: three carnitine acetyltransferases are essential in a carnitine-dependent
strain [Establishes CAT2 role in carnitine metabolism]'
- term:
id: GO:0004092
label: carnitine O-acetyltransferase activity
evidence_type: IEA
original_reference_id: GO_REF:0000120
review:
summary: 'This is a computational annotation from combined automated annotation
methods (IEA from GO_REF:0000120). It represents the same core function as
the IBA and IMP annotations, supported by EC classification 2.3.1.7 and RHEA
reaction mapping. This annotation is redundant with the higher-quality IBA
and IMP evidence but provides additional confirmation of the enzymatic function.'
action: ACCEPT
additional_reference_ids:
- GO_REF:0000120
- term:
id: GO:0005743
label: mitochondrial inner membrane
evidence_type: IEA
original_reference_id: GO_REF:0000044
review:
summary: 'This annotation specifies the precise mitochondrial localization of
CAT2 (mitochondrial isoform). This is a computational annotation derived from
UniProtKB subcellular location vocabulary mapping (GO_REF:0000044) and is
accurate. The UniProt record explicitly states the primary isoform localizes
to the mitochondrial inner membrane as a peripheral membrane protein. The
term is appropriately specific and supported by the documented isoform structure.'
action: ACCEPT
additional_reference_ids:
- GO_REF:0000044
- term:
id: GO:0005777
label: peroxisome
evidence_type: IEA
original_reference_id: GO_REF:0000044
review:
summary: 'This is a computational annotation from UniProtKB subcellular location
vocabulary mapping (GO_REF:0000044) documenting the peroxisomal localization
of the CAT2 peroxisomal isoform. This is accurate and supported by direct
experimental evidence (IDA from PMID:18427809, PMID:22375831). The annotation
appropriately represents the documented alternative isoform.'
action: ACCEPT
additional_reference_ids:
- GO_REF:0000044
- term:
id: GO:0006629
label: lipid metabolic process
evidence_type: IEA
original_reference_id: GO_REF:0000043
review:
summary: 'This annotation is derived from UniProtKB keyword mapping (GO_REF:0000043,
KW-0443: Lipid metabolism). CAT2 is involved in lipid metabolism through its
role in the carnitine shuttle for fatty acid oxidation in peroxisomes. However,
this is an indirect and broad annotation. While not incorrect, the more specific
process term "carnitine-dependent fatty acid oxidation" or "fatty acid metabolic
process" would be more informative.'
action: KEEP_AS_NON_CORE
reason: 'This term is accurate but overly general. CAT2 contributes to lipid
metabolism through the carnitine shuttle facilitating fatty acid oxidation,
but this is a secondary effect of its primary function. The term represents
a higher-level process that encompasses the more specific functions already
captured by GO:0006631 (fatty acid metabolic process) and GO:0009437 (carnitine
metabolic process).'
- term:
id: GO:0006631
label: fatty acid metabolic process
evidence_type: IEA
original_reference_id: GO_REF:0000043
review:
summary: 'This annotation is derived from UniProtKB keyword mapping (GO_REF:0000043,
KW-0276: Fatty acid metabolism). CAT2 is directly involved in fatty acid oxidation
through the carnitine shuttle mechanism. In yeast, peroxisomes are the primary
site of fatty acid oxidation, and CAT2 is essential for this process by facilitating
the transport of acetyl groups from peroxisomes to mitochondria. This is supported
by PMID:11329169, which documents the essential role of all three CAT enzymes
in carnitine-dependent fatty acid metabolism.'
action: ACCEPT
supported_by:
- reference_id: PMID:11329169
supporting_text: 'L-carnitine and all three CATs are essential for growth
on non-fermentable carbon sources in a strain with a disrupted CIT2 gene
[Documents CAT2 role in fatty acid metabolism]'
- term:
id: GO:0016740
label: transferase activity
evidence_type: IEA
original_reference_id: GO_REF:0000043
review:
summary: 'This annotation is derived from UniProtKB keyword mapping (GO_REF:0000043,
KW-0808: Transferase). CAT2 is indeed a transferase, catalyzing the transfer
of acetyl groups from acetyl-CoA to carnitine. However, this is a very broad
and general molecular function term. The specific function is much better
represented by GO:0004092 (carnitine O-acetyltransferase activity) and GO:0016746
(acyltransferase activity), which provide more informative classification.'
action: KEEP_AS_NON_CORE
reason: 'While technically correct, this term is too general and uninformative.
GO:0004092 provides the specific enzymatic classification, and this broader
term adds little additional value. It represents a parent term of the more
specific acyltransferase activity.'
- term:
id: GO:0016746
label: acyltransferase activity
evidence_type: IEA
original_reference_id: GO_REF:0000120
review:
summary: 'This annotation is derived from automated annotation methods (GO_REF:0000120)
mapping InterPro domain IPR000542 (Carnitine/choline acetyltransferase family).
CAT2 is indeed an acyltransferase, specifically catalyzing the transfer of
an acetyl group (an acyl group) from acetyl-CoA to carnitine. This is a reasonable
intermediate-level classification between the general transferase activity
and the specific carnitine O-acetyltransferase activity.'
action: ACCEPT
additional_reference_ids:
- GO_REF:0000120
- term:
id: GO:0005515
label: protein binding
evidence_type: IPI
original_reference_id: PMID:27107014
review:
summary: 'This annotation is from a protein-protein interaction study (IPI,
PMID:27107014), documenting interaction with a human ortholog (UniProtKB:Q9H190).
While this indicates CAT2 has protein binding capability, the term "protein
binding" is non-specific and uninformative. Every protein binds to other molecules;
this does not distinguish the biological function. Without knowledge of the
specific interaction partner or functional consequence, this annotation provides
minimal functional insight.'
action: MARK_AS_OVER_ANNOTATED
reason: 'The term "protein binding" is too vague and generic. This annotation
documents a protein-protein interaction from an inter-species study, but provides
no functional context. The interaction partner appears to be a human ortholog
used for comparative analysis rather than a specific yeast interaction. More
informative would be specific binding partner information or functional roles
(e.g., substrate/product binding). This annotation does not represent a core
biological function of the enzyme.'
supported_by:
- reference_id: PMID:27107014
supporting_text: An inter-species protein-protein interaction network
across vast evolutionary distance.
- term:
id: GO:0005777
label: peroxisome
evidence_type: IDA
original_reference_id: PMID:22375831
review:
summary: 'This annotation documents peroxisomal localization based on direct
evidence (IDA). PMID:22375831 is a proteomics study of the peroxisomal importomer
that identified CAT2 as a component or interactor in peroxisomal protein import
machinery. This provides direct evidence for peroxisomal localization. The
annotation is accurate and supported by the experimental approach.'
action: ACCEPT
supported_by:
- reference_id: PMID:22375831
supporting_text: 'Identification of core components and transient interactors
of the peroxisomal importomer by dual-track stable isotope labeling with
amino acids in cell culture analysis [Direct identification in peroxisomal
protein import studies]'
- term:
id: GO:0005739
label: mitochondrion
evidence_type: HDA
original_reference_id: PMID:24769239
review:
summary: 'This annotation documents mitochondrial localization based on homologous
annotation (HDA). PMID:24769239 is a quantitative proteomics study of the
mitochondrial proteome that identified CAT2. This provides evidence for mitochondrial
localization through detection of the protein in mitochondrial preparations.
The annotation is accurate and represents core localization information.'
action: ACCEPT
additional_reference_ids:
- PMID:24769239
supported_by:
- reference_id: PMID:24769239
supporting_text: 2014 Apr 24. Quantitative variations of the
mitochondrial proteome and phosphoproteome during fermentative and
respiratory growth in Saccharomyces cerevisiae.
- term:
id: GO:0005739
label: mitochondrion
evidence_type: HDA
original_reference_id: PMID:14576278
review:
summary: 'This annotation documents mitochondrial localization based on homologous
annotation (HDA). PMID:14576278 is a proteomics study of the Saccharomyces
cerevisiae mitochondrial proteome, providing evidence for CAT2 identification
in mitochondrial preparations. This corroborates the mitochondrial localization
annotation.'
action: ACCEPT
additional_reference_ids:
- PMID:14576278
supported_by:
- reference_id: PMID:14576278
supporting_text: The proteome of Saccharomyces cerevisiae
mitochondria.
- term:
id: GO:0005739
label: mitochondrion
evidence_type: HDA
original_reference_id: PMID:16823961
review:
summary: 'This annotation documents mitochondrial localization based on homologous
annotation (HDA). PMID:16823961 is a multidimensional proteomics study toward
the complete yeast mitochondrial proteome, providing another line of proteomic
evidence for CAT2 identification in mitochondrial preparations. This further
corroborates the mitochondrial localization.'
action: ACCEPT
additional_reference_ids:
- PMID:16823961
supported_by:
- reference_id: PMID:16823961
supporting_text: 'Toward the complete yeast mitochondrial proteome: multidimensional
separation techniques for mitochondrial proteomics.'
- term:
id: GO:0004092
label: carnitine O-acetyltransferase activity
evidence_type: IMP
original_reference_id: PMID:8420957
review:
summary: 'This annotation documents carnitine O-acetyltransferase activity based
on direct experimental evidence (IMP - Inferred from Mutant Phenotype). PMID:8420957
is the original cloning paper that established CAT2 identity through gene
disruption studies and enzyme activity measurements. This is the highest-quality
evidence for the enzymatic function. The disruption phenotype (decreased acetylcarnitine
content and altered pyruvate metabolism) directly demonstrates the catalytic
activity of CAT2.'
action: ACCEPT
supported_by:
- reference_id: PMID:8420957
supporting_text: 'The acetylcarnitine content of these cells decreased significantly.
A search in the PIR protein data base revealed that besides the known
carnitine acyltransferases, choline acyltransferases are highly homologous
to yeast CAT [Establishes CAT2 enzymatic function]'
- term:
id: GO:0005739
label: mitochondrion
evidence_type: IDA
original_reference_id: PMID:18427809
review:
summary: 'This annotation documents mitochondrial localization based on direct
experimental evidence (IDA). PMID:18427809 is a functional study of carnitine
acetyltransferases in yeast that documents CAT2 localization and function
in stress protection. The direct identification provides evidence for the
mitochondrial localization of the primary isoform. This is high-quality evidence
for the subcellular localization.'
action: ACCEPT
supported_by:
- reference_id: PMID:18427809
supporting_text: 'Carnitine and carnitine acetyltransferases in the yeast
Saccharomyces cerevisiae: a role for carnitine in stress protection [Documents
CAT2 localization]'
- term:
id: GO:0005777
label: peroxisome
evidence_type: IDA
original_reference_id: PMID:18427809
review:
summary: 'This annotation documents peroxisomal localization based on direct
experimental evidence (IDA). PMID:18427809 provides experimental evidence
for the peroxisomal isoform of CAT2. The study demonstrates that CAT2 localizes
to both mitochondria and peroxisomes, consistent with the documented alternative
initiation products that generate two isoforms with different localizations.'
action: ACCEPT
supported_by:
- reference_id: PMID:18427809
supporting_text: 'Carnitine and carnitine acetyltransferases in the yeast
Saccharomyces cerevisiae: a role for carnitine in stress protection [Demonstrates
CAT2 localization to both compartments]'
- term:
id: GO:0009437
label: carnitine metabolic process
evidence_type: IMP
original_reference_id: PMID:11329169
review:
summary: 'This annotation documents carnitine metabolic process involvement
based on direct experimental evidence (IMP - Inferred from Mutant Phenotype).
PMID:11329169 is a comprehensive study of carnitine-dependent metabolic activities
that demonstrates CAT2 is one of three essential carnitine acetyltransferases.
The mutant selection strategy and complementation analysis provide strong
genetic evidence for CAT2 involvement in carnitine metabolism.'
action: ACCEPT
supported_by:
- reference_id: PMID:11329169
supporting_text: 'L-carnitine is required for the transfer of activated
acyl-groups across intracellular membranes in eukaryotic organisms. In
Saccharomyces cerevisiae, peroxisomal membranes are impermeable to acetyl-CoA
[Essential role in carnitine-dependent metabolism]'
references:
- 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:0000044
title: Gene Ontology annotation based on UniProtKB/Swiss-Prot Subcellular
Location vocabulary mapping, accompanied by conservative changes to GO
terms applied by UniProt
findings: []
- id: GO_REF:0000120
title: Combined Automated Annotation using Multiple IEA Methods
findings: []
- id: PMID:11329169
title: 'Carnitine-dependent metabolic activities in Saccharomyces cerevisiae:
three carnitine acetyltransferases are essential in a carnitine-dependent strain.'
findings: []
- id: PMID:14576278
title: The proteome of Saccharomyces cerevisiae mitochondria.
findings: []
- id: PMID:16823961
title: 'Toward the complete yeast mitochondrial proteome: multidimensional separation
techniques for mitochondrial proteomics.'
findings: []
- id: PMID:18427809
title: 'Carnitine and carnitine acetyltransferases in the yeast Saccharomyces
cerevisiae: a role for carnitine in stress protection.'
findings: []
- id: PMID:22375831
title: Identification of core components and transient interactors of the
peroxisomal importomer by dual-track stable isotope labeling with amino
acids in cell culture analysis.
findings: []
- id: PMID:24769239
title: Quantitative variations of the mitochondrial proteome and
phosphoproteome during fermentative and respiratory growth in
Saccharomyces cerevisiae.
findings: []
- id: PMID:27107014
title: An inter-species protein-protein interaction network across vast
evolutionary distance.
findings: []
- id: PMID:8420957
title: Cloning and sequencing of a cDNA encoding Saccharomyces cerevisiae
carnitine acetyltransferase. Use of the cDNA in gene disruption studies.
findings: []