THE UNCHARGED SURFACE-FEATURES SURROUNDING THE ACTIVE-SITE OF ESCHERICHIA-COLI DSBA ARE CONSERVED AND ARE IMPLICATED IN PEPTIDE BINDING

DsbA is a protein-folding catalyst from the periplasm of Escherichia c oli that interacts with newly translocated polypeptide substrate and c atalyzes the formation of disulfide bonds in these secreted proteins. The precise nature of the interaction between DsbA and unfolded substr ate is not known. Here, we give a detailed analysis of the DsbA crysta l structure, now refined to 1.7 Angstrom, and present a proposal for i ts interaction with peptide. The crystal structure of DsbA implies fle xibility between the thioredoxin and helical domains that may be an im portant feature for the disulfide transfer reaction. A hinge point for domain motion is identified-the typo IV beta-turn Phe 63-Met 64-Gly 6 5-Gly 66, which connects the two domains. Three unique features on the active site surface of the DsbA molecule-a groove, hydrophobic pocket , and hydrophobic patch-form an extensive uncharged surface surroundin g the active-sits disulfide. Residues that contribute to these surface features are shown to be generally conserved in eight DsbA homologues . Furthermore, the residues immediately surrounding the active-site di sulfide are uncharged in all nine DsbA proteins. A model for DsbA-pept ide interaction has been derived from the structure of a human thiored oxin:peptide complex. This shows that peptide could interact with DsbA in a manner similar to that with thioredoxin. The active-site disulfi de and all three surrounding uncharged surface features of DsbA could, in principle, participate in the binding or stabilization of peptide.