Maturation of Exported Proteins in Escherichia coli

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 μM). The site and kinetics of processing were investigated for OmpA, LamB and OmpF proteins and for maltose binding protein and TEM β‐lactamase. With regard to sites of processing, no fundamental difference between outer membrane and periplasmic proteins was observed. For maltose binding protein and TEM β‐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 μM) 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.