Structural characterisation of the virulence-associated protein VapG from the horse pathogen Rhodococcus equi.
Virulence and host range in Rhodococcus equi depends on the variable pathogenicity island of their virulence plasmids. Notable gene products are a family of small secreted virulence-associated proteins (Vaps) that are critical to intramacrophagic proliferation. Equine-adapted strains, which cause severe pyogranulomatous pneumonia in foals, produce a cell-associated VapA that is necessary for virulence, alongside five other secreted homologues. In the absence of biochemical insight, attention has turned to the structures of these proteins to develop a functional hypothesis. Recent studies have described crystal structures for VapD and a truncate of the VapA orthologue of porcine-adapted strains, VapB. Here, we crystallised the full-length VapG and determined its structure by molecular replacement. Electron density corresponding to the N-terminal domain was not visible suggesting that it is disordered. The protein core adopted a compact elliptical, anti-parallel β-barrel fold with β1-β2-β3-β8-β5-β6-β7-β4 topology decorated by a single peripheral α-helix unique to this family. The high glycine content of the protein allows close packing of secondary structural elements. Topologically, the surface has no indentations that indicate a nexus for molecular interactions. The distribution of polar and apolar groups on the surface of VapG is markedly uneven. One-third of the surface is dominated by exposed apolar side-chains, with no ionisable and only four polar side-chains exposed, giving rise to an expansive flat hydrophobic surface. Other surface regions are more polar, especially on or near the α-helix and a belt around the centre of the β-barrel. Possible functional significance of these recent structures is discussed.
Department of Applied Sciences, Faculty of Health and Life Sciences, Northumbria University, Newcastle upon Tyne NE1 8ST, UK.
Tebekeme
T
Okoko
Structural Biology Laboratory, Department of Chemistry, University of York, Heslington, York YO10 5DD, UK.
Elena V
EV
Blagova
Structural Biology Laboratory, Department of Chemistry, University of York, Heslington, York YO10 5DD, UK. Electronic address: jean.whittingham@york.ac.uk.
Jean L
JL
Whittingham
Department of Applied Sciences, Faculty of Health and Life Sciences, Northumbria University, Newcastle upon Tyne NE1 8ST, UK.
Lynn G
LG
Dover
Structural Biology Laboratory, Department of Chemistry, University of York, Heslington, York YO10 5DD, UK.
Anthony J
AJ
Wilkinson
D000193:Actinomycetales Infections / Q000382:microbiology / Q000662:veterinary*; D000818:Animals; D001426:Bacterial Proteins / Q000737:chemistry / Q000235:genetics; D018360:Crystallography, X-Ray / Q000662:veterinary; D044404:Genomic Islands / Q000235:genetics; D006734:Horse Diseases / Q000382:microbiology*; D006736:Horses; D010957:Plasmids / Q000235:genetics; D017433:Protein Structure, Secondary; D016929:Rhodococcus equi / Q000737:chemistry* / Q000235:genetics / Q000472:pathogenicity; D013552:Swine; D014774:Virulence
D001426:Bacterial Proteins; C460867:VapG protein, Rhodococcus equi
Protein Structure; Rhodococcus equi; VapA; VapG; Virulence-associated protein