Conformational changes of the chaperone SecB upon binding to a model substrate--bovine pancreatic trypsin inhibitor (BPTI).

SecB is a homotetrameric cytosolic chaperone that forms part of the protein translocation machinery in E. coli. Due to SecB, nascent polypeptides are maintained in an unfolded translocation-competent state devoid of tertiary structure and thus are guided to the translocon.