Defective secretion of maltose- and ribose-binding proteins caused by a truncated periplasmic protein in Escherichia coli

Abstract

The secretion in Escherichia coli of a C-terminally truncated periplasmic enzyme from Salmonella typhimurium, the glpQ-encoded glycerolphosphate phosphodiesterase, was studied. Plasmid pRH100, carrying the truncated glpQ gene, directs the synthesis of a 30,000-molecular-weight (30 K) protein that is processed to a mature 27.5 K protein. (The mature wild-type protein is a 38 K protein.) The truncated protein is not released into the periplasm but remains membrane associated, although it becomes protease sensitive after conversion of cells to spheroplasts. The presence of pRH100 strongly reduces the amount of some other proteins in the periplasm, including the maltose- and ribose-binding proteins. The reduction does not occur at the level of transcription or early translation, as shown by lacZ fusions to the gene coding for the structural gene of the maltose-binding protein. Outer membrane proteins are not affected. A hydroxylamine-induced mutation in the sequence of glpQ corresponding to the mature polypeptide overcomes the inhibitory effect of pRH100. The mutated gene no longer directs the synthesis of the 30/27.5 K protein but directs that of a new 19 K protein which is not membrane bound. We propose that sorting signals in the mature GIpQ protein are necessary for effective translocation to the periplasm and that the C-terminal third of the protein is essential for release into the periplasm.

Mechanism of bactericidal action of aminoglycosides.

“…A short C-terminal deletion has been reported to shift the E. coli 13-lactamase from the periplasm to the membrane (43). While similar findings with the maltose-binding protein were thought to reflect attachment of aggregated protein to the membrane, rather than retention in the membrane (40), a truncated glycerophosphate phosphodiesterase seems definitely to be shifted from periplasm to membrane, since it interferes with the secretion of other periplasmic proteins (34). In such studies, it would be of interest to test for effects not only on protein export, but also on the integrity of the osmotic barrier.…”