Identification of the E2-binding residues in the N-terminal domain of E1 of a prokaryotic pyruvate dehydrogenase complex

The psp (phage-shock protein) operon of Escherichia coli is induced when the bacteria are infected by filamentous phage and under several other stress conditions. The physiological role of the individual Psp proteins is still not known. We demonstrate here that the last gene of the operon, pspE, encodes a thiosulfate:cyanide sulfurtransferase (EC 2.8.1.1; rhodanese). Kinetic analysis revealed that catalysis occurs via a double displacement mechanism as described for other rhodaneses. The K(m)s for SSO3(2-) and CN- were 4.6 and 27 mM, respectively.