Succinyl-CoA synthetase (SCS) catalyzes the only substrate-level phosphorylation step in the tricarboxylic acid cycle. Human GTP-specific SCS (GTPSCS), an αβ-heterodimer, was produced in Escherichia coli. The purified protein crystallized from a solution containing tartrate, CoA and magnesium chloride, and a crystal diffracted to 1.52 Å resolution. Tartryl-CoA was discovered to be bound to GTPSCS. The CoA portion lies in the amino-terminal domain of the α-subunit and the tartryl end extends towards the catalytic histidine residue. The terminal carboxylate binds to the phosphate-binding site of GTPSCS.
Keywords: catalysis; succinyl-CoA synthetase; thioesters; tricarboxylic acid cycle.