Structural characterisation of the virulence-associated protein VapG from the horse pathogen Rhodococcus equi

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JournalVeterinary Microbiology
DatePublished - Aug 2015
Issue number1-2
Volume179
Number of pages11
Pages (from-to)42-52
Original languageEnglish

Abstract

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. Equineadapted 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, antiparallel ß-barrel fold with ß1-ß2-ß3-bß8-bß5-ß6-ß7-ß4 topology decorated by a single peripheral a-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 sidechains exposed, giving rise to an expansive flat hydrophobic surface. Other surface regions are more polar, especially on or near the a-helix and a belt around the centre of the ß-barrel. Possible functional significance of these recent structures is discussed.

    Research areas

  • Protein Structure, Rhodococcus equi, VapA, VapG, Virulence-associated protein

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