Glutamyl-tRNA reductase catalyzes the conversion of glutamyl-tRNA to glutamate-1-semialdehyde, initiating the synthesis of tetrapyrrole. Whereas tRNAs are generally associated with peptide bond formation in protein translation, here the tRNA activates glutamate in the initiation of tetrapyrrole biosynthesis in archaea, plants and many bacteria. In the first step, activated glutamate is reduced to glutamate-1-semi-aldehyde via the NADPH dependent glutamyl-tRNA reductase. Glutamyl-tRNA reductase forms a V-shaped dimer. Each monomer has 3 domains: an N-terminal catalytic domain, a classic nucleotide binding domain, and a C-terminal dimerization domain. Although the representative structure 1GPJ lacks a bound NADPH, a theoretical binding pocket has been described. (PMID 11172694). Amino acid dehydrogenase (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.
Jiyao W et al.(2023). "The conserved domain database in 2023.",