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Title: EsxB, a secreted protein from Bacillus anthracis forms two distinct helical bundles

The EsxB protein from Bacillus anthracis belongs to the WXG100 family, a group of proteins secreted by a specialized secretion system. We have determined the crystal structures of recombinant EsxB and discovered that the small protein (~10 kDa), comprised of a helix-loop-helix (HLH) hairpin, is capable of associating into two different helical bundles. The two basic quaternary assemblies of EsxB are an antiparallel (AP) dimer and a rarely observed bisecting U (BU) dimer. This structural duality of EsxB is believed to originate from the heptad repeat sequence diversity of the first helix of its HLH hairpin, which allows for two alternative helix packing. The flexibility of EsxB and the ability to form alternative helical bundles underscore the possibility that this protein can serve as an adaptor in secretion and can form hetero-oligomeric helix bundle(s) with other secreted members of the WXG100 family, such as EsxW. The highly conserved WXG motif is located within the loop of the HLH hairpin and is mostly buried within the helix bundle suggesting that its role is mainly structural. The exact functions of the motif, including a proposed role as a secretion signal, remain unknown.
Authors:
 [1] ;  [2] ;  [1] ;  [2] ;  [1] ;  [2] ;  [2]
  1. Argonne National Lab. (ANL), Argonne, IL (United States)
  2. Argonne National Lab. (ANL), Argonne, IL (United States); Univ. of Chicago, Chicago, IL (United States)
Publication Date:
OSTI Identifier:
1212699
Grant/Contract Number:
AC02-06CH11357; GM074942; GM094585
Type:
Accepted Manuscript
Journal Name:
Protein Science
Additional Journal Information:
Journal Volume: 24; Journal Issue: 9; Journal ID: ISSN 0961-8368
Publisher:
The Protein Society
Research Org:
Argonne National Laboratory (ANL), Argonne, IL (United States)
Sponsoring Org:
USDOE Office of Science (SC), Biological and Environmental Research (BER) (SC-23)
Country of Publication:
United States
Language:
English
Subject:
59 BASIC BIOLOGICAL SCIENCES type VII secretion system; ESAT-6 like secretion system; WXG family; EsxB; helix bundle; antiparallel dimer; bisecting U dimer; tetramer