Major proteins of the outer cell envelope membrane ofEscherichia coli K-12: Multiple species of protein I

Abstract

Protein I, one of the major outer membrane proteins ofE. coli, in a number of strains exists as two electrophoretically separable species Ia and Ib. Two phages, TuIa and TuIb, have been found which use, as receptors, proteins Ia and Ib, respectively. Selection for resistance to phage TuIb yielded mutants still possessing protein Ia and missing protein Ib (Ia+ Ib-). Selection in this background, for resistance to phage TuIa yielded one class of mutants missing both species of protein I and another synthesizing a new species of protein I, polypeptide Ic. Tryptic fingerprints of Ia and Ic are very similar and the sequence of 8 N-terminal amino acids is identical for Ia and Ic. Yet, Ic showed an entirely different pattern of cyanogen bromide fragments than that of protein Ia. With another example (cyanogen bromide fragments of protein II*, with and without performic acid oxidation) it is shown that protein modification can lead to gross changes of the electrophoretic mobility of cyanogen bromide fragments. It is not unlikely that all protein I species observed so far represent in vivo modifications of one and the same polypeptide chain. A genetic analysis together with data from other laboratories revealed that at least 4 widely separated chromosomal loci are involved in the expression of the protein I species known to date.