INSERTION OF AN OUTER-MEMBRANE PROTEIN IN ESCHERICHIA-COLI REQUIRES ACHAPERONE-LIKE PROTEIN

Only one of the characterized components of the main terminal branch o f the general secretory pathway (GSP) in Gram-negative bacteria, GspD, is an integral outer membrane protein that could conceivably form a c hannel to permit protein transport across this membrane. PulD, a membe r of the GspD protein family required for pullulanase secretion by Kle bsiella oxytoca, is shown here to form outer membrane-associated compl exes which are not readily dissociated by SDS treatment, The outer mem brane association of PulD is absolutely dependent on another component of the GSP, the outer membrane-anchored lipoprotein PulS, Furthermore , the absence of PulS resulted in limited proteolysis of PulD and caus ed induction of the so-called phage shock response, as measured by inc reased expression of the pspA gene, We propose that PulS may be the fi rst member of a new family of periplasmic chaperones that are specific ally required for the insertion of a group of outer membrane proteins into this membrane, PulS is only the second component of the main term inal branch of the GSP for which a precise function can be proposed.