Type 1 glutamine amidotransferase (GATase1)-like domain found in homoserine trans-succinylase (HTS)
Type 1 glutamine amidotransferase (GATase1)-like domain found in homoserine trans-succinylase (HTS). HTS, the first enzyme in methionine biosynthesis in Escherichia coli, transfers a succinyl group from succinyl-CoA to homoserine forming succinyl homoserine. It has been suggested that the succinyl group of succinyl-CoA is initially transferred to an enzyme nucleophile before subsequent transfer to homoserine. The catalytic triad typical of GATase1 domains is not conserved in this GATase1-like domain. However, in common with GATase1 domains a reactive cys residue is found in the sharp turn between a beta strand and an alpha helix termed the nucleophile elbow. It has been proposed that this cys is in the active site of the molecule. However, as succinyl has been found bound to a conserved lysine residue, this conserved cys may play a role in dimer formation. HTS activity is tightly regulated by several mechanisms including feedback inhibition and proteolysis. It represents a critical control point for cell growth and viability.