N-TAIL TRANSLOCATION OF MATURE BETA-LACTAMASE ACROSS THE ESCHERICHIA-COLI CYTOPLASMIC MEMBRANE

Mature beta-lactamase was attached to the N-terminus of human glycopho rin C, an N-out membrane protein lacking a cleavable signal peptide (a n N-tail membrane protein). When synthesised in Escherichia coli more than 30% of the intact mature beta-lactamase-glycophorin C molecules a ssembled N-out, C-in into the cytoplasmic membrane. The N-tail translo cated beta-lactamase folded into an enzymatically active form, but it was more susceptible to proteolysis than the equivalent portion of bet a-lactamase-glycophorin C synthesised with an N-terminal signal peptid e. Its translocation was virtually abolished when the N-out domain of glycophorin C was truncated or when the basic residues C-terminally na nking the glycophorin C membrane-spanning segment were replaced with n eutral ones. (C) 1997 Federation of European Biochemical Societies.