TY - JOUR
T1 - Structural characterisation of the virulence-associated protein VapG from the horse pathogen Rhodococcus equi
AU - Okoko, Tebekeme
AU - Blagova, Elena V.
AU - Whittingham, Jean L.
AU - Dover, Lynn G.
AU - Wilkinson, Anthony J.
PY - 2015/8
Y1 - 2015/8
N2 - 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.
AB - 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.
KW - Protein Structure
KW - Rhodococcus equi
KW - VapA
KW - VapG
KW - Virulence-associated protein
UR - http://www.scopus.com/inward/record.url?scp=84942821178&partnerID=8YFLogxK
U2 - 10.1016/j.vetmic.2015.01.027
DO - 10.1016/j.vetmic.2015.01.027
M3 - Article
AN - SCOPUS:84942821178
SN - 0378-1135
VL - 179
SP - 42
EP - 52
JO - Veterinary Microbiology
JF - Veterinary Microbiology
IS - 1-2
ER -