Structural analysis of BPSV-CBP.

<p>(A) Structure-based sequence alignment of BPSV-CBP and ORFV-CBP. Amino acid sequence of BPSV-CBP is compared with the sequence of ORFV-CBP represented in a published crystal structure (PDB: 4P5I). Identical and conserved residues are highlighted in light and dark cyan, respectively (definition of conserved amino acid residues follows ClustalW). The structurally conserved region (boxed) predicts BPSV-CBP has a common β-sheet sandwich structure including three α-helices (yellow cylinders) and two β-sheets (arrows). The β-sheet I (blue arrow) enriched with basic residues, while the β-sheet II (red arrow) comprises acidic and hydrophobic residues, and serves as chemokine-binding surface. The chemokine-binding residues exposed at the β-sheet II are indicated by stars. Six conserved cysteines forming disulphide bonds are highlighted in pair colours; yellow, green and purple. The N-linked glycosylation sites and dimerization interfaces are symbolized by ● and ♦, respectively. The red dashed line shows a distinct region in the connecting loop between β-strand 2 and 3 of BPSV-CBP. The numbering is based on the ORFV-CBP. (B) Cartoon representation of the ORFV-CBP monomer shows a typical β-sandwich fold. Glycosylation sites (dark blue ball and stick representation) are seen on both β-sheets. The major difference in the BPSV-CBP occurred in a connecting loop between β strands 2 and 3 (circle). The colour scheme for secondary structures is identical to Fig 2A. (C) Mapping of conserved residues of the BPSV-CBP onto the crystal structure of ORFV-CBP in complex with CCL2 (yellow ribbon diagram). The colour scheme of identical light and conserved dark cyan residues follows Fig 2A. A localized hydrophobic interaction pins-down the chemokine’s N-loop (red) into the CBP’s hydrophobic pocket (middle diagram), and the positively charged 20s loop of the chemokine (blue) sites within the negatively charged groove on the β-sheet II (left diagram). The altered amino acid residues on the β-sheet II (in purple) would not interfere with chemokine binding. Glycosylation sites are shown as dark blue ball and stick representation.