NAD(P) binding domain of glutamate dehydrogenase, leucine dehydrogenase, phenylalanine dehydrogenase, and valine dehydrogenase
Amino acid dehydrogenase (DH) is a widely distributed family of enzymes that catalyzes the oxidative deamination of an amino acid to its keto acid and ammonia with concomitant reduction of NAD(P)+. This subfamily includes glutamate, leucine, phenylalanine, and valine DHs. Glutamate DH is a multi-domain enzyme that catalyzes the reaction from glutamate to 2-oxyoglutarate and ammonia in the presence of NAD or NADP. It is present in all organisms. Enzymes involved in ammonia assimilation are typically NADP+-dependent, while those involved in glutamate catabolism are generally NAD+-dependent. As in other NAD+-dependent DHs, monomers in this family have 2 domains separated by a deep cleft. Here the c-terminal domain contains a modified NAD-binding Rossmann fold with 7 rather than the usual 6 beta strands and one strand anti-parrallel to the others. Amino acid DH-like NAD(P)-binding domains are members of the Rossmann fold superfamily and include glutamate, leucine, and phenylalanine DHs, methylene tetrahydrofolate DH, methylene-tetrahydromethanopterin DH, methylene-tetrahydropholate DH/cyclohydrolase, Shikimate DH-like proteins, malate oxidoreductases, and glutamyl tRNA reductase. Amino acid DHs catalyze the deamination of amino acids to keto acids with NAD(P)+ as a cofactor. The NAD(P)-binding Rossmann fold superfamily includes a wide variety of protein families including NAD(P)- binding domains of alcohol DHs, tyrosine-dependent oxidoreductases, glyceraldehyde-3-phosphate DH, lactate/malate DHs, formate/glycerate DHs, siroheme synthases, 6-phosphogluconate DH, amino acid DHs, repressor rex, NAD-binding potassium channel domain, CoA-binding, and ornithine cyclodeaminase-like domains. These domains have an alpha-beta-alpha configuration. NAD binding involves numerous hydrogen and van der Waals contacts.