JB Accepts, published online ahead of print on 23 October 2009

This Article Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Reprints and Permissions Copyright Information Books from ASM Press MicrobeWorld Google Scholar Articles by Callahan, B. Articles by Derbyshire, K. M. PubMed PubMed Citation Articles by Callahan, B. Articles by Derbyshire, K. M.

 Previous Article  |  Next Article 

J. Bacteriol. doi:10.1128/JB.01032-09
Copyright (c) 2009, American Society for Microbiology and/or the Listed Authors/Institutions. All Rights Reserved.

Conservation of structure and protein-protein interactions mediated by the secreted mycobacterial proteins EsxA, EsxB, and EspA

Brian Callahan, Kiet Nguyen, Alissa Collins, Kayla Valdes, Michael Caplow, David K. Crossman, Adrie J.C. Steyn, Leslie Eisele, and Keith M. Derbyshire^*

Division of Genetics, Wadsworth Center, New York State Department of Health, Department of Biochemistry and Biophysics, UNC, Chapel Hill, NC; Department of Microbiology, University of Alabama at Birmingham, AL 35294; Division of Translational Medicine, Wadsworth Center, New York State Department of Health, and Department of Biomedical Sciences, University at Albany, Albany, New York 12201-2002, USA

^* To whom correspondence should be addressed. Email: keith.derbyshire{at}wadsworth.org.

Mycobacterium tuberculosis EsxA and EsxB proteins are founding members of the WXG100(WXG) protein family, characterized by their small size (100aa) and conserved WXG amino acid motif. M. tuberculosis contains eleven tandem pairs of WXG genes; each gene pair is thought to be co-expressed to form a heterodimer. The precise role of these proteins in the biology of M. tuberculosis is unknown, but several of the heterodimers are secreted, which is important for virulence. However, WXG proteins are not simply virulence factors, as non-pathogenic mycobacteria also express and secrete these proteins. Here, we show that three WXG heterodimers have similar structures and properties to the MtbEsxBA heterodimer, regardless of their host species and apparent biological function. Biophysical studies indicate that WXG proteins from M. tuberculosis (EsxG, H), Mycobacterium smegmatis, (EsxA, B), and Corynebacterium diphtheriae (EsxA, B) are heterodimers and fold into a predominately -helical structure. An in vivo protein-protein interaction assay was modified to identify proteins that interact specifically with the native WXG100 heterodimer. MtbEsxA and MtbEsxB were fused into a single polypeptide, MtbEsxBA, to create a biomimetic bait of the native heterodimer. The MtbEsxBA bait showed a specific association with several esx-1 encoded proteins and EspA, a virulence protein secreted by ESX-1. The MtbEsxBA fusion was also utilized to identify residues in both EsxA and EsxB that are important for establishing protein interactions with Rv3871 and EspA. Together, the results are consistent with a model in which WXG proteins perform similar biological roles in both virulent and non-virulent species.