Putative D-isomer specific 2-hydroxyacid dehydrogenase
2-Hydroxyacid dehydrogenases catalyze the conversion of a wide variety of D-2-hydroxy acids to their corresponding keto acids. The general mechanism is (R)-lactate + acceptor to pyruvate + reduced acceptor. Formate/glycerate and related dehydrogenases of the D-specific 2-hydroxyacid dehydrogenase superfamily include groups such as formate dehydrogenase, glycerate dehydrogenase, L-alanine dehydrogenase, and S-adenosylhomocysteine hydrolase. Despite often low sequence identity, these proteins typically have a characteristic arrangement of 2 similar subdomains of the alpha/beta Rossmann fold NAD+ binding form. The NAD+ binding domain is inserted within the linear sequence of the mostly N-terminal catalytic domain, which has a similar domain structure to the internal NAD binding domain. Structurally, these domains are connected by extended alpha helices and create a cleft in which NAD is bound, primarily to the C-terminal portion of the 2nd (internal) domain. Some related proteins have similar structural subdomains but with a tandem arrangement of the catalytic and NAD-binding subdomains in the linear sequence. While many members of this family are dimeric, alanine DH is hexameric and phosphoglycerate DH is tetrameric. Formate dehydrogenase (FDH) catalyzes the NAD+-dependent oxidation of formate ion to carbon dioxide with the concomitant reduction of NAD+ to NADH. FDHs of this family contain no metal ions or prosthetic groups. Catalysis occurs though direct transfer of the hydride ion to NAD+ without the stages of acid-base catalysis typically found in related dehydrogenases. FDHs are found in all methylotrophic microorganisms in energy production and in the stress responses of plants.
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