Job contenders: roles of the β-barrel assembly machinery and the translocation and assembly module in autotransporter secretion

5 years ago

Job contenders: roles of the β-barrel assembly machinery and the translocation and assembly module in autotransporter secretion

Raffaele Ieva, Cécile Albenne

In Gram-negative bacteria, autotransporters secrete effector protein domains that are linked to virulence. Although they were once thought to be simple and autonomous secretion machines, mounting evidence reveals that multiple factors of the bacterial envelope are necessary for autotransporter assembly. Secretion across the outer membrane of their soluble effector “passenger domain” is promoted by the assembly of an outer membrane-spanning “β-barrel domain”. Both reactions require BamA, an essential component of the β-barrel assembly machinery (BAM complex) that catalyzes the final reaction step by which outer membrane proteins are integrated into the lipid bilayer. A large amount of data generated in the last decade has shed key insights onto the mechanistic coordination of autotransporter β-barrel domain assembly and passenger domain secretion. These results, together with the recently solved structures of the BAM complex, offer an unprecedented opportunity to discuss a detailed model of autotransporter assembly. Importantly, some autotransporters benefit from the presence of an additional machinery, the translocation and assembly module (TAM), a two-membrane spanning complex, which contains a BamA-homologous subunit. Although it remains unclear how the BAM complex and the TAM cooperate, it is evident that multiple preparatory steps are necessary for efficient autotransporter biogenesis. This article is protected by copyright. All rights reserved. Autotransporters are a class of virulence factors secreted by Gram-negative bacteria. Although these proteins were initially thought to be self-sufficient for secretion, recent work has shown that multiple factors, including two translocases in the bacterial outer membrane, are involved in their biogenesis. We discuss the recent literature on the roles of the β-barrel assembly machinery (BAM) complex and the translocation and assembly module (TAM) in autotransporter secretion.

Publisher URL: http://onlinelibrary.wiley.com/resolve/doi

DOI: 10.1111/mmi.13832