Mutations that affect the folding of ribose-binding protein selected as suppressors of a defect in export in Escherichia-coli

Abstract

It has been proposed (Randall, L. L., and Hardy, S. J. S. (1986) Cell 46, 921-928) that export of protein involves a kinetic partitioning between the pathway that leads to productive export and the pathway that leads to the folding of polypeptides into a stable conformation that is incompatible with export. As predicted from this model, a decrease in the rate of export of maltose-binding protein to the periplasmic space in Escherichia coli resulting from a defect in the leader sequence was able to be partially overcome by a mutation that slowed the folding of the precursor, thereby increasing the time in which the polypeptide was competent for export. (Liu, G., Topping, T. B., Cover, W. H., and Randall, L. L. (1988) J. Biol. Chem. 263, 14790-14793). Here we describe mutations of the gene encoding ribose-binding protein that were selected as suppressors of a defect in export of that protein and that alter the folding pathway. We propose that selection of such suppressors may provide a general method to obtain mutations that affect the folding properties of any protein that can be expressed and exported in E. coli.