Mechanistic link between beta barrel assembly and the initiation of autotransporter secretion

作者：Pavlova Olga; Peterson Janine H; Ieva Raffaele; Bernstein Harris D^*

来源：Proceedings of the National Academy of Sciences, 2013, 110(10): E938-E947.

DOI：10.1073/pnas.1219076110

• membrane protein assembly
• outer membrane proteins
• protein translocation

Autotransporters are bacterial virulence factors that contain an N-terminal extracellular ("passenger") domain and a C-terminal beta barrel ("beta") domain that anchors the protein to the outer membrane. The beta domain is required for passenger domain secretion, but its exact role in autotransporter biogenesis is unclear. Here we describe insights into the function of the beta domain that emerged from an analysis of mutations in the Escherichia coli O157:H7 autotransporter EspP. We found that the G1066A and G1081D mutations slightly distort the structure of the beta domain and delay the initiation of passenger domain translocation. Site-specific photocrosslinking experiments revealed that the mutations slow the insertion of the beta domain into the outer membrane, but do not delay the binding of the beta domain to the factor that mediates the insertion reaction (the Bam complex). Our results demonstrate that the beta domain does not simply target the passenger domain to the outer membrane, but promotes translocation when it reaches a specific stage of assembly. Furthermore, our results provide evidence that the Bam complex catalyzes the membrane integration of beta barrel proteins in a multistep process that can be perturbed by minor structural defects in client proteins.

• 出版日期2013-3-5