NCGR_LOCUS29329

Existing Annotations Review

GO Term	Evidence	Action	Reason
GO:0004072 aspartate kinase activity	IEA GO_REF:0000120	ACCEPT	Summary: Aspartate kinase activity is the core N-terminal enzymatic function of this bifunctional AK-HSD enzyme. The protein contains a well-defined AA_kinase domain (Pfam PF00696), aspartate kinase signature (PROSITE PS00324), and specific CDD domain cd04257 (AAK_AK-HSDH). Multiple InterPro signatures (IPR001341, IPR018042) confirm the aspartate kinase classification. EC 2.7.2.4 is the correct enzyme commission number for this activity. Reason: Strong domain evidence from multiple databases (InterPro, PROSITE, CDD, Pfam) consistently supports aspartate kinase activity. This is a core catalytic function of the bifunctional enzyme, catalyzing L-aspartate + ATP -> 4-phospho-L-aspartate + ADP. Supporting Evidence: UniProt:A0A811PKG6 Belongs to the aspartokinase family (N-terminal section) PMID:8507831 the isolated carrot cDNA appears to encode a bifunctional aspartokinase-homoserine dehydrogenase enzyme
GO:0004412 homoserine dehydrogenase activity	IEA GO_REF:0000120	ACCEPT	Summary: Homoserine dehydrogenase activity is the core C-terminal enzymatic function. The protein contains a Homoserine_dh domain (Pfam PF00742), HSD catalytic site (PROSITE PS01042), NAD-binding domain (PF03447), and the bifunctional-specific InterPro signature IPR011147. PANTHER subfamily PTHR43070:SF5 specifically classifies this as homoserine dehydrogenase. EC 1.1.1.3 is correct. Reason: Strong domain evidence from multiple databases. This is the second core catalytic function of the bifunctional enzyme, catalyzing L-aspartate 4-semialdehyde + NAD(P)H -> L-homoserine + NAD(P)+. The reaction is the third step in the aspartate pathway. Supporting Evidence: UniProt:A0A811PKG6 Belongs to the homoserine dehydrogenase family (C-terminal section) PMID:8507831 the isolated carrot cDNA appears to encode a bifunctional aspartokinase-homoserine dehydrogenase enzyme
GO:0016491 oxidoreductase activity	IEA GO_REF:0000002	MARK AS OVER ANNOTATED	Summary: Oxidoreductase activity is a parent term of homoserine dehydrogenase activity (GO:0004412). While technically correct, it is redundant with the more specific GO:0004412 annotation already present. Reason: This is a true but overly general annotation. The more specific GO:0004412 (homoserine dehydrogenase activity) already captures this function precisely. Annotating both the parent and child term is redundant.
GO:0050661 NADP binding	IEA GO_REF:0000002	ACCEPT	Summary: The homoserine dehydrogenase domain uses NAD(P)+ as cofactor. The protein contains a NAD-binding Rossmann-fold domain (Pfam PF03447, InterPro IPR005106). The enzyme can use both NAD+ and NADP+ as cofactors based on the UniProt catalytic activity annotations. Reason: NADP binding is supported by the NAD(P)-binding Rossmann-fold domain and is functionally relevant to the homoserine dehydrogenase activity. The enzyme uses NADP+ as an alternative cofactor to NAD+. Supporting Evidence: UniProt:A0A811PKG6 L-homoserine + NADP(+) = L-aspartate 4-semialdehyde + NADPH + H(+)
GO:0006520 amino acid metabolic process	IEA GO_REF:0000002	MARK AS OVER ANNOTATED	Summary: Amino acid metabolic process is a high-level parent of the more specific biosynthetic process annotations already present (GO:0009067, GO:0009088, GO:0009090). While technically correct, it adds no additional information. Reason: Redundant with the more specific biological process annotations. The protein is specifically involved in aspartate family amino acid biosynthesis (GO:0009067), threonine biosynthesis (GO:0009088), and homoserine biosynthesis (GO:0009090), all of which are children of this term.
GO:0006531 aspartate metabolic process	IEA GO_REF:0000117	ACCEPT	Summary: The aspartate kinase domain directly uses L-aspartate as substrate, phosphorylating it to 4-phospho-L-aspartate. This is the committed first step in aspartate-derived amino acid biosynthesis. Reason: Correct and informative. The enzyme directly metabolizes aspartate via the aspartate kinase reaction. While the downstream pathway annotations (GO:0009067 etc.) are more specific about the biosynthetic outcome, this term correctly captures the substrate utilization aspect. Supporting Evidence: UniProt:A0A811PKG6 L-aspartate + ATP = 4-phospho-L-aspartate + ADP
GO:0008652 amino acid biosynthetic process	IEA GO_REF:0000002	MARK AS OVER ANNOTATED	Summary: Amino acid biosynthetic process is a parent term of the more specific aspartate family amino acid biosynthetic process (GO:0009067) already annotated. Reason: Redundant with GO:0009067 (aspartate family amino acid biosynthetic process), which is a more specific child term that better captures the function.
GO:0009067 aspartate family amino acid biosynthetic process	IEA GO_REF:0000118	ACCEPT	Summary: This term encompasses the biosynthesis of aspartate-derived amino acids (lysine, methionine, threonine, asparagine). As a bifunctional AK-HSD, this enzyme catalyzes the first step common to all branches and the third step in the threonine/methionine branch. Reason: This is the most appropriate level of specificity for the overall pathway role. The enzyme acts at the branch point of multiple amino acid biosynthetic pathways derived from aspartate. TreeGrafter classification via PANTHER:PTN009166675 supports this annotation. Supporting Evidence: PMID:8507831 Aspartokinase (EC 2.7.2.4) and homoserine dehydrogenase (EC 1.1.1.3) catalyze steps in the pathway for the synthesis of lysine, threonine, and methionine from aspartate
GO:0009088 threonine biosynthetic process	IEA GO_REF:0000041	ACCEPT	Summary: The enzyme catalyzes steps 1 and 3 of the 5-step threonine biosynthetic pathway from L-aspartate. Step 1 (AK) phosphorylates aspartate, and step 3 (HSD) reduces aspartate semialdehyde to homoserine, which is then converted to threonine. The ACT domains provide threonine-mediated feedback inhibition, indicating a direct regulatory link to threonine levels. Reason: Directly supported by UniPathway annotations (UPA00050) and the enzyme's dual catalytic activities. Threonine feedback inhibition of the ACT domains further confirms the enzyme's role in threonine biosynthesis. Supporting Evidence: UniProt:A0A811PKG6 L-threonine biosynthesis; L-threonine from L-aspartate: step 1/5 and step 3/5
GO:0009090 L-homoserine biosynthetic process	IEA GO_REF:0000118	ACCEPT	Summary: The homoserine dehydrogenase domain directly produces L-homoserine from L-aspartate 4-semialdehyde. This is the most direct product of the HSD enzymatic activity. Reason: Directly catalyzed by the HSD domain. L-homoserine is the direct product of the enzyme's C-terminal catalytic activity and serves as a precursor for both threonine and methionine biosynthesis. TreeGrafter classification supports this annotation. Supporting Evidence: UniProt:A0A811PKG6 L-methionine biosynthesis via de novo pathway; L-homoserine from L-aspartate: step 3/3
GO:0009507 chloroplast	IEA GO_REF:0000044	ACCEPT	Summary: Chloroplast localization is expected for plant AK-HSD enzymes. The aspartate-derived amino acid biosynthetic pathway operates in the chloroplast/plastid in plants. The protein has a predicted N-terminal transit peptide consistent with chloroplast targeting. Reason: Consistent with known biology of plant aspartate pathway enzymes. All steps of the pathway except the final methylation of homocysteine to methionine occur in the chloroplast. The UniProt subcellular location annotation supports this. Supporting Evidence: UniProt:A0A811PKG6 SUBCELLULAR LOCATION: Plastid, chloroplast