The active site of O-acetylserine sulfhydrylase is the anchor point for bienzyme complex formation with serine acetyltransferase.
The biosynthesis of cysteine in bacteria and plants is carried out by a two-step pathway, catalyzed by serine acetyltransferase (SAT) and O-acetylserine sulfhydrylase (OASS; O-acetylserine [thiol] lyase). The aerobic form of OASS forms a tight bienzyme complex with SAT in vivo, termed cysteine synthase. We have determined the crystal structure of OASS in complex with a C-terminal peptide of SAT required for bienzyme complex formation. The binding site of the peptide is at the active site of OASS, and its C-terminal carboxyl group occupies the same anion binding pocket as the alpha-carboxylate of the O-acetylserine substrate of OASS. These results explain the partial inhibition of OASS by SAT on complex formation as well as the competitive dissociation of the complex by O-acetylserine.
Huang
Bin
B
Department of Biochemistry, Albert Einstein College of Medicine, 1300 Morris Park Ave., Bronx, NY 10461, USA.
Vetting
Matthew W
MW
Roderick
Steven L
SL
D000123:Acetyltransferases / Q000737:chemistry*; D001665:Binding Sites; D003547:Cysteine Synthase / Q000737:chemistry*; D008958:Models, Molecular; D020836:Protein Structure, Quaternary; D051050:Serine O-Acetyltransferase
D000123:Acetyltransferases; D051050:Serine O-Acetyltransferase; D003547:Cysteine Synthase