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The structure of the β-barrel assembly machinery complex

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Science  08 Jan 2016:
Vol. 351, Issue 6269, pp. 180-186
DOI: 10.1126/science.aad3460

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Going in with a BAM

Integral membrane proteins in bacterial outer membranes play roles in nutrient import and infectivity. These proteins are folded into a barrel shape composed of β-strands and inserted into the outer membrane by the β-barrel assembly machinery (BAM) complex. Bakelar et al. determined the crystal structure of a four-component BAM subcomplex. The structure of a central β barrel in BAM changes in the presence of the accessory components to create a lateral opening that may be involved in how BAM inserts proteins into the outer membrane.

Science, this issue p. 180

Abstract

β-Barrel outer membrane proteins (OMPs) are found in the outer membranes of Gram-negative bacteria and are essential for nutrient import, signaling, and adhesion. A 200-kilodalton five-component complex called the β-barrel assembly machinery (BAM) complex has been implicated in the biogenesis of OMPs. We report the structure of the BAM complex from Escherichia coli, revealing that binding of BamCDE modulates the conformation of BamA, the central component, which may serve to regulate the BAM complex. The periplasmic domain of BamA was in a closed state that prevents access to the barrel lumen, which indicates substrate OMPs may not be threaded through the barrel during biogenesis. Further, conformational shifts in the barrel domain lead to opening of the exit pore and rearrangement at the lateral gate.

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