cds1

Summary: This annotation represents a cysteine biosynthetic function, but experimental evidence from Ma et al. (2021) demonstrates that VC1061/cds1 functions primarily in cysteine catabolism to produce H2S, not biosynthesis. The IBA annotation is based on phylogenetic inference from orthologs that may include cysteine synthases, but the V. cholerae enzyme has been experimentally characterized as a cysteine desulfhydrase that degrades cysteine.

Reason: The annotation is incorrect for this specific gene. Ma et al. (2021) clearly demonstrate that VC1061 is the principal enzyme for H2S production FROM cysteine degradation, not cysteine biosynthesis. Deletion of VC1061 drastically reduces H2S production from cysteine, indicating a catabolic rather than biosynthetic role. The phylogenetic inference from IBA incorrectly propagated function from related cysteine synthases (SF194/SF162) that catalyze the reverse reaction. MSA analysis of PTHR10314 family reveals: (1) SF135 (Cds1/desulfhydrases) has a distinct active site signature motif (ASSGST) vs synthases (PTSGNTG); (2) SF135 shares only ~24% sequence identity with synthases, less than synthases share with each other (43%); (3) SF135 has the longest branch length (0.528) from the family root, indicating greatest divergence and neo-functionalization; (4) different EC class - 4.4.1.1 (lyase/catabolism) vs 2.5.1.47 (transferase/biosynthesis). The source proteins in the IBA WITH/FROM field (P0ABK5/CysK, P35520/CBS, P16703/CysM) are from SF194/SF162 synthase subfamilies, but Q9KT44/VC1061 is in SF135 which evolved a catabolic function.

Summary: Cytoplasmic localization is consistent with the function of this PLP-dependent enzyme. UniProt annotation (HAMAP-Rule:MF_00868) also indicates cytoplasmic localization, supported by both homology inference and computational prediction.

Reason: Cytoplasmic localization is well-supported by both phylogenetic inference (IBA) and computational methods. PLP-dependent enzymes of this class are typically cytoplasmic, and there is no evidence for any alternative localization. This represents a core aspect of the protein's function.

Summary: This annotation is based on EC:2.5.1.47 mapping, which assigns cysteine synthase activity (O-acetyl-L-serine + H2S -> L-cysteine + acetate). However, the primary experimentally demonstrated activity for VC1061 is the opposite reaction - L-cysteine desulfhydrase activity (EC 4.4.1.1), which degrades cysteine to produce H2S.

Reason: The EC mapping to cysteine synthase (EC 2.5.1.47) is incorrect for this enzyme. Ma et al. (2021) demonstrated that VC1061 is the principal H2S-producing enzyme from cysteine degradation in V. cholerae. UniProt correctly annotates this enzyme with EC 4.4.1.1 (L-cysteine desulfhydrase) via HAMAP-Rule:MF_00868. The correct molecular function term is GO:0080146 (L-cysteine desulfhydrase activity).

Proposed replacements: L-cysteine desulfhydrase activity

Summary: Duplicate cytoplasm annotation from combined automated methods. This is consistent with the IBA annotation and represents a valid localization for this enzyme.

Reason: This annotation is redundant with the IBA annotation for cytoplasm but remains valid. Multiple lines of computational evidence (UniRule, HAMAP, ARBA) support cytoplasmic localization for Cds1-family enzymes.

Summary: Lyase activity is a high-level term that correctly captures the general enzymatic class of L-cysteine desulfhydrases. The enzyme catalyzes a carbon-sulfur lyase reaction (C-S bond cleavage), which is classified under lyases (EC 4.x.x.x).

Reason: While this is a broad term, it is not incorrect. L-cysteine desulfhydrase (EC 4.4.1.1) is indeed a lyase that cleaves C-S bonds. This annotation provides useful high-level classification, though more specific terms (GO:0080146) should also be present. Keeping this annotation maintains appropriate ontology hierarchy representation.

Summary: This biological process annotation correctly captures the catabolic role of Cds1. The enzyme converts L-cysteine to pyruvate (plus H2S and ammonia), which is precisely the process described by this GO term.

Reason: This annotation accurately represents the core biological process in which Cds1 participates. Ma et al. (2021) demonstrated that VC1061 is the principal enzyme for cysteine-derived H2S production, and the canonical desulfhydrase reaction yields pyruvate as a product. This annotation derived from InterPro:IPR047586 (Cds1 family) is correct and represents a core function of the gene.

Summary: PLP binding is essential for Cds1 catalytic activity. The enzyme belongs to the TrpB-like PLP-dependent superfamily, and UniProt annotation indicates the PLP binding site at Lys54 (N6-(pyridoxal phosphate)lysine modification).

Reason: This annotation is well-supported by sequence features and domain architecture. The protein contains a TrpB-like PALP fold (IPR001926, PF00291) and has a defined PLP binding site at Lys54. PLP is the required cofactor for cysteine desulfhydrase activity, making this annotation essential for understanding the enzyme's mechanism.

Summary: This is a high-level biological process term indicating involvement in amino acid metabolism. While correct, it is very general compared to the more specific GO:0019450 (L-cysteine catabolic process to pyruvate) that is also annotated.

Reason: This annotation is correct but provides less specific information than GO:0019450. It is acceptable to retain as it provides ontological context and is not incorrect. The ARBA machine learning model correctly identified the metabolic role of this enzyme.

Summary: This is the correct molecular function term for Cds1 based on experimental evidence. Ma et al. (2021) demonstrated that VC1061 is the principal enzyme for H2S production from L-cysteine in V. cholerae. The reaction is: L-cysteine + H2O = ammonia + pyruvate + hydrogen sulfide + H+.

Reason: This annotation should be added as the primary molecular function for Cds1. The existing GO:0004124 (cysteine synthase activity) annotation is incorrect for this enzyme. Genetic deletion experiments clearly demonstrate that VC1061 is the key enzyme for cysteine-to-H2S conversion. This term (GO:0080146) precisely matches EC 4.4.1.1 assigned by HAMAP.

Summary: Cds1 is the principal enzyme responsible for hydrogen sulfide (H2S) biosynthesis in V. cholerae through cysteine degradation. Ma et al. (2021) demonstrated that deletion of VC1061 drastically reduces H2S production from cysteine.

Reason: This biological process annotation should be added to reflect the primary physiological role of Cds1 in V. cholerae. The enzyme-derived H2S has important downstream effects including oxidative stress resistance and enhanced catalase activity. This term captures the biosynthetic aspect of H2S production that is central to the enzyme's function.

Summary: The H2S produced by Cds1 protects V. cholerae from oxidative stress by enhancing catalase (KatB) activity. Deletion mutants show approximately 10-fold lower viability under H2O2 stress compared to wild-type.

Reason: Experimental evidence from Ma et al. (2021) demonstrates that Cds1-derived H2S is essential for oxidative stress resistance. The phenotype (reduced survival under H2O2) of cbs/VC1061 deletion mutants supports IMP evidence for involvement in this process. However, this may be considered a downstream effect rather than a core function of the enzyme, so could alternatively be marked as KEEP_AS_NON_CORE.