Marín E, Bodelón G, Fernández LÁ
Comparative analysis of the biochemical and functional properties of C-terminal domains of autotransporters.
J Bacteriol. 2010 Nov;192(21):5588-602
Authors: Marín E, Bodelón G, Fernández LÁ
Autotransporters (ATs) are the largest group of proteins secreted by Gram-negative bacteria and include many virulence factors from human pathogens. ATs are synthesized as large precursors with a C-terminal domain that is inserted in the outer membrane (OM) and is essential for the translocation of an N-terminal passenger domain to the extracellular milieu. Several mechanisms have been proposed for AT secretion. Self-translocation models suggest transport across a hydrophilic channel formed by an internal pore of the ?-barrel or by the oligomerization of C-terminal domains. Alternatively, an assisted-translocation model suggests that transport employs a conserved machinery of the bacterial OM such as the Bam complex. In this work we have investigated AT secretion by carrying out a comparative study to analyze the conserved biochemical and functional features of different C-terminal domains selected from ATs of gammaproteobacteria, betaproteobacteria, alphaproteobacteria, and epsilonproteobacteria. Our results indicate that C-terminal domains having an N-terminal ?-helix and a ?-barrel constitute functional transport units for the translocation of peptides and immunoglobulin domains with disulfide bonds. In vivo and in vitro analyses show that multimerization is not a conserved feature in AT C-terminal domains. Furthermore, we demonstrate that the deletion of the conserved ?-helix severely impairs ?-barrel folding and OM insertion and thereby blocks passenger domain secretion. These observations suggest that the AT ?-barrel without its ?-helix cannot form a stable hydrophilic channel in the OM for protein translocation. The implications of our data for an understanding of AT secretion are discussed.
PMID: 20802036 [PubMed - in process]