# 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.

## Key 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.