Making a beta-barrel: assembly of outer membrane proteins in Gram-negative bacteria

Abstract

The outer membrane (OM) of Gram-negative bacteria is an essential organelle that serves as a selective permeability barrier by keeping toxic compounds out of the cell while allowing vital nutrients in. How the OM and its constituent lipid and protein components are assembled remains an area of active research. In this review, we describe our current understanding of how outer membrane proteins (OMPs) are delivered to and then assembled in the OM of the model Gram-negative organism Escherichia coli.

Figure 1. The OMP assembly pathway in E. coli

Outer membrane proteins (OMPs) are synthesized as unfolded precursors in the cytoplasm and translocated across the inner membrane (IM) via the Sec translocase. Once in the periplasm, chaperones recognize unfolded OMPs and prevent them from forming misfolded aggregates. The multi-subunit Bam complex folds and inserts OMPs into the outer membrane (OM).