Maturation of exported proteins in Escherichia coli. Requirement for energy, site and kinetics of processing

Abstract

Precursor forms of periplasmic and outer membrane proteins were accumulated in phenethyl-alcohol-treated cells in membrane fractions. After removal of phenethyl alcohol, maturation occurred in the absence but not in the presence of carbonylcyanide m-chlorophenylhydrazone (30 microM). The site and kinetics of processing were investigated for OmpA, LamB and OmpF proteins and for maltose binding protein and TEM beta-lactamase. With regard to sites of processing, no fundamental difference between outer membrane and periplasmic proteins was observed. For maltose binding protein and TEM beta-lactamase, maturation, like that of outer membrane protein precursors, occurred in membrane fractions. Processing of pro-OmpA protein was about as fast as that of pro-LamB protein whereas pro-OmpF protein appeared to mature more slowly. While carbonylcyanide m-chlorophenylhydrazone (30 microM) prevented processing of all precursor forms, arsenate, which alters formation of ATP even when it was used at 1 mM, did not totally prevent maturation occurring. These results are discussed with regard to the biosynthesis and assembly of exported proteins.