CONPUDRAFT_136560

Summary: Root catalytic activity from InterPro IPR015955 (LDH/glycoside hydrolase family 4 C-terminal domain superfamily).

Reason: Correct but uninformative. The protein is a type-1 malate dehydrogenase (TIGR01772, IPR010097, PIRSF000102) with the PIRSR proton-acceptor and NAD/substrate-binding residues. The specific activity GO:0030060 L-malate dehydrogenase (NAD+) activity, which this gene already carries, is the supported refinement.

Proposed replacements: L-malate dehydrogenase (NAD+) activity

Summary: Cytoplasm from TreeGrafter, inherited from the deep PAINT node PTN000166149, where cytoplasm is asserted for the whole type-1 MDH clade.

Reason: PAINT places cytoplasm at PTN000166149, an ancestral node seeded by cytosolic, peroxisomal and mitochondrial MDHs alike (for example S. cerevisiae MDH1, MDH2 and MDH3). In GO the mitochondrion is part of the cytoplasm, so the row is true for this protein. It is uninformative here because GO:0005739 mitochondrion, accepted in this review, already entails it. The row should not be read as a cytosolic location. The protein has a presequence-like N-terminal extension and no PTS1 (see bioinformatics RESULTS), and it shares PANTHER subfamily SF73 with yeast mitochondrial MDH1.

Summary: Mitochondrion from TreeGrafter, inherited from the PAINT node PTN000899458, which also carries the TCA cycle.

Reason: Following the root-organelle policy, I checked the basis of this synthesis row. PAINT asserts mitochondrion at PTN000899458, the mitochondrial-MDH clade from which the target's TreeGrafter node PTN000899503 descends. Three independent sequence lines agree with that placement. (1) The target has a 32-residue segment before the conserved GxGGxG motif; it carries 5 Arg/Lys, no Asp/Glu and 10 Ser/Thr, the composition of a matrix-targeting presequence. Yeast Mdh1p, the experimentally mitochondrial ortholog (identity 0.63), has an equivalent 17-residue presequence. UniProt's Pfam PF00056 domain feature, which starts at residue 27, independently corroborates an N-terminal extension of about 26 residues ahead of the conserved domain. (2) The protein lacks a PTS1, whereas the C. puteana paralog A0A5M3MC96 ends in SKL. (3) PANTHER assigns the target to subfamily PTHR11540:SF73, the subfamily that contains yeast MDH1 (P17505), the experimentally mitochondrial MDH. Yeast peroxisomal MDH3 (P32419) is in a different subfamily, SF72, which does not contain the target. This is a membership argument; the subfamily names are not localization calls (SF16 is also named mitochondrial and contains yeast cytosolic MDH2, P22133). CDD cd01337 (MDH_glyoxysomal_mitochondrial) covers both glyoxysomal and mitochondrial MDHs, so it cannot separate the two and is not counted. No experimental localization exists for a C. puteana MDH, so the claim is inferential, but it holds.

Summary: Tricarboxylic acid cycle, from the combined InterPro/PANTHER pipeline.

Reason: Mitochondrial NAD-MDH catalyses the malate-to-oxaloacetate step that closes the TCA cycle, so the enzyme performs a step of the process. PAINT asserts the TCA cycle at the mitochondrial node PTN000899458, and the target has the presequence that places it in the matrix where the cycle runs. High MDH activity in brown-rot fungi has been tied to TCA/glyoxylate-cycle operation feeding oxalate synthesis in Fomitopsis palustris. That work used whole-cell extracts and did not resolve isozymes.

Summary: Generic oxidoreductase activity from InterPro IPR001236 (lactate/malate DH N-terminal domain).

Reason: Correct but general. The supported specific activity is GO:0030060 L-malate dehydrogenase (NAD+) activity, already carried by this gene. Type-1 family membership and the conserved catalytic and NAD-binding residues support it.

Proposed replacements: L-malate dehydrogenase (NAD+) activity

Summary: NAD(P)-dependent CH-OH oxidoreductase activity from the lactate/malate DH superfamily signatures.

Reason: Correct but less specific than the evidence supports. The lactate/malate DH superfamily signatures cannot distinguish LDH from MDH. The type-1 MDH signatures (TIGR01772, IPR010097) and the MDH-type substrate-binding residues place the protein as an NAD-dependent malate dehydrogenase, so GO:0030060, already carried by this gene, is the refinement.

Proposed replacements: L-malate dehydrogenase (NAD+) activity

Summary: NAD-dependent L-malate dehydrogenase activity (EC 1.1.1.37), the core activity, inferred from family membership.

Reason: Every family classifier places the protein among type-1 malate dehydrogenases (NCBIfam TIGR01772, InterPro IPR010097, PIRSF000102, CDD cd01337, PANTHER PTHR11540:SF73). PIRSR annotates the proton-acceptor His and the NAD(+)- and substrate-binding positions. PAINT asserts this activity at PTN000166149, an ancestor of the target's node. There is no experimental characterization of this protein.

Summary: Proposed mitochondrial matrix location, beside the accepted mitochondrion rows.

Reason: The root-organelle policy asks for at least two independent lines before adding a sub-compartment, and two are present. (1) Sequence: a presequence-like, Arg-rich N-terminal extension with no acidic residues and no transmembrane segment; the yeast ortholog's equivalent extension is a cleaved matrix-targeting presequence. (2) Function: the NAD-MDH step of the TCA cycle runs in the matrix, where the NAD+/NADH pool and the other cycle enzymes are; a protein of the mitochondrial-MDH clade (PAINT PTN000899458: mitochondrion and TCA cycle) has no plausible role on another side of the inner membrane. The row is an inference (IC) with no direct assay.