L-2-hydroxyisocapronate dehydrogenases and some bacterial L-lactate dehydrogenases
L-2-hydroxyisocapronate dehydrogenase (HicDH) catalyzes the conversion of a variety of 2-oxo carboxylic acids with medium-sized aliphatic or aromatic side chains. This subfamily is composed of HicDHs and some bacterial L-lactate dehydrogenases (LDH). LDHs catalyze the last step of glycolysis in which pyruvate is converted to L-lactate. Bacterial LDHs can be non-allosteric or may be activated by an allosteric effector such as fructose-1,6-bisphosphate. Members of this subfamily with known structures such as the HicDH of Lactobacillus confusus, the non-allosteric LDH of Lactobacillus pentosus, and the allosteric LDH of Bacillus stearothermophilus, show that they exist as homotetramers. The HicDH-like subfamily is part of the NAD(P)-binding Rossmann fold superfamily, which includes a wide variety of protein families including the NAD(P)-binding domains of alcohol dehydrogenases, tyrosine-dependent oxidoreductases, glyceraldehyde-3-phosphate dehydrogenases, formate/glycerate dehydrogenases, siroheme synthases, 6-phosphogluconate dehydrogenases, aminoacid dehydrogenases, repressor rex, and NAD-binding potassium channel domains, among others.