Not All Bacterial Outer-Membrane Proteins Are β-Barrels

TL;DR

This paper shows that not all outer-membrane proteins in Gram-negative bacteria are β-barrels, challenging a long-held belief in the field.

Contribution

The paper introduces Wza and related proteins as examples of helical transmembrane segments in bacterial outer membranes.

Findings

Wza is an octomeric helical barrel in the bacterial outer membrane.

Other members of the Outer-Membrane Polysaccharide Exporter family may also have helical transmembrane segments.

Type IV secretion system proteins also contain helical transmembrane segments.

Abstract

The discovery of Wza, an octomeric helical barrel integral bacterial outer-transmembrane protein, has challenged the widely held understanding that all integral outer-membrane proteins of Gram-negative bacteria are closed β-barrels composed of transmembrane β- strands. Wza is a member of the Outer-Membrane Polysaccharide Exporter family and our bioinformatics analysis suggests that other members of the family may also contain outer-membrane transmembrane segments that are helical. A review of the literature indicates that in addition to Wza, outer-membrane core complex proteins of the type IV secretion systems also contain transmembrane segments that are helical.

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