High selectivity with low specificity: how SecB has solved the paradox of chaperone binding

Fundamental to the function of all molecular chaperones is their amazing ability to selectively and rapidly bind proteins in non-native states. Chaperones modulate a kinetic partitioning among the alternative pathways open to polypeptides within a cell, so that the proper pathway is taken. Here we review studies of SecB, a chaperone in Escherichia coli dedicated to facilitation of protein export, and emphasize the features that enable it to bind rapidly with high affinity and selectivity in the absence of consensus in sequence. The concepts discussed are likely to be generally applicable to chaperones.