Analysis of Functional Domains on Glutamate Synthase

Glutamate synthases (GOGAT) were analyzed to identify the functional binding domains of the substrate (glutamine) and cofactors (FMN, NAD(P)H, FAD, [3Fe-4S] and [4Fe-4S] clusters and ferredoxin) on this enzyme. The published amino acid sequences of six different NAD(P)Hdependent GOGATs (NAD(P)H-GOGAT) and ten different ferredoxin-dependent GOGATs (Fd-GOGAT) were used for this analysis. The amino acid sequences of these sixteen GOGATs were compared with the amino acid sequences of aminotransferases for glutamine, flavoproteins for FMN, flavoproteins and pyridine-nucleotide-dependent enzymes for FAD and NAD(P)H, iron-sulfur proteins for [3Fe4S] and [4Fe-4S] clusters and ferredoxin-dependent enzymes for ferredoxin. It was determined that Fd-GOGAT has one domain each for glutamine, FMN and [3Fe-4S] cluster and two domains each for FAD and ferredoxin; the NADPH-GOGAT α subunit has the same domains as FdGOGAT except for the ferredoxin domains, and β subunit has one domain each for NADPH and FAD and two domains for two [4Fe-4S]clusters; NADH-GOGAT has the same domains as NADPHGOGAT.