Secretion and Membrane Localization of Proteins in<i>Escherichia Coli</i>

TLDR

The envelope of *E. coli* is composed of an outer membrane and a cytoplasmic membrane, with the periplasmic space between them containing distinct proteins. This review examines how proteins are directed to their final locations within the bacterial envelope. Peptide extensions of about 20 amino acids at the N‑termini of precursor proteins share common features, and a loop model is proposed to explain their role in secretion across the cytoplasmic membrane.

Abstract

The envelope of Escherichia coli consists of two distinct membranes, the outer membrane and the cytoplasmic membrane. The space between the two membranes is called the periplasmic space, and each fraction contains its own specific proteins. In this review, it is discussed how proteins are localized in their final locations in the envelope. Proteins localized in the outer membrane and the periplasmic space as well as transmembranous proteins in the cytoplasmic membranes appear to be produced from their precursors which have peptide extensions of about 20 amino acid residues at the amino terminal ends. General features for the peptide extension are deduced from the known sequences of the peptide extensions, and, based on their known properties, a hypothesis (loop model) is proposed to explain the possible functions of the peptide extension during the mechanism of secretion across the cytoplasmic membrane.