Peptide binding by chaperone SecB: implications for recognition of nonnative structure.

The molecular basis for recognition of nonnative proteins by the molecular chaperone SecB was investigated with an in vitro assay based on the protection of SecB from proteolysis when a ligand is bound. The SecB tetramer has multiple binding sites for positively charged peptides. When the peptide binding sites are occupied, the complex undergoes a conformational change to expose hydrophobic sites that bind the fluorescent probe 1-anilinonaphthalene-8-sulfonate. A model is proposed for interaction of nonnative polypeptides with both hydrophilic and hydrophobic sites on SecB.