SECRET domain of variola virus CrmB protein can be a member of poxviral type II chemokine-binding proteins family

Abstract

BackgroundVariola virus (VARV) the causative agent of smallpox, eradicated in 1980, have wide spectrum of immunomodulatory proteins to evade host immunity. Recently additional biological activity was discovered for VARV CrmB protein, known to bind and inhibit tumour necrosis factor (TNF) through its N-terminal domain homologous to cellular TNF receptors. Besides binding TNF, this protein was also shown to bind with high affinity several chemokines which recruit B- and T-lymphocytes and dendritic cells to sites of viral entry and replication. Ability to bind chemokines was shown to be associated with unique C-terminal domain of CrmB protein. This domain named SECRET (Smallpox virus-Encoded Chemokine Receptor) is unrelated to the host proteins and lacks significant homology with other known viral chemokine-binding proteins or any other known protein.FindingsDe novo modelling of VARV-CrmB SECRET domain spatial structure revealed its apparent structural homology with cowpox virus CC-chemokine binding protein (vCCI) and vaccinia virus A41 protein, despite low sequence identity between these three proteins. Potential ligand-binding surface of modelled VARV-CrmB SECRET domain was also predicted to bear prominent electronegative charge which is characteristic to known orthopoxviral chemokine-binding proteins.ConclusionsOur results suggest that SECRET should be included into the family of poxviral type II chemokine-binding proteins and that it might have been evolved from the vCCI-like predecessor protein.

Structures of Orf Virus Chemokine Binding Protein in Complex with Host Chemokines Reveal Clues to Broad Binding Specificity

“…A related group includes the A41 protein from vaccinia virus (VACV), which also binds selected CC and CXC chemokines, but a subset different to vCCI (Bahar et al, 2008;Ruiz-Argü ello et al, 2008). A41 and vCCI are sometimes referred to together as type-II CKBPs (Seet and McFadden, 2002;Antonets et al, 2010). An additional group, more recently described, includes the SECRET (Smallpox virus Encoded Chemokine Receptor) domain from the variola virus protein, CrmB and the ectromelia virus (EV) protein, CrmD (Antonets et al, 2010;Xue et al, 2011).…”

“…A41 and vCCI are sometimes referred to together as type-II CKBPs (Seet and McFadden, 2002;Antonets et al, 2010). An additional group, more recently described, includes the SECRET (Smallpox virus Encoded Chemokine Receptor) domain from the variola virus protein, CrmB and the ectromelia virus (EV) protein, CrmD (Antonets et al, 2010;Xue et al, 2011). These proteins each contain two domains, one that binds tumor necrosis factor and another named SECRET that binds, with variable affinity, to selected CC and CXC chemokines (Antonets et al, 2010;Xue et al, 2011).…”

Immune modulation by virus-encoded secreted chemokine binding proteins

“…The fact that all members of the SECRET family bind the same set of chemokines, despite their low sequence similarity, suggests that the SECRET domain has a specific folding to bind chemokines either independently or fused to TNFRs. De novo modeling of VARV CrmB SECRET domain spatial structure revealed structural homology with CPXV 35-kDa and VACV A41 proteins (Antonets et al, 2010). The three dimensional structure of the SECRET domain alone or complexed with a low affinity binding chemokine, CX3CL1, was solved and confirmed that it shares the same ␤-sandwich topology with the 35-kDa and A41 poxvirus CKBPs (Xue et al, 2011) (Fig.…”

TNF-Binding domain of the variola virus CrmB protein synthesized in Escherichia coli cells effectively interacts with human TNF

“…The amplified DNA fragment encoding the TNF BD protein was inserted into the open reading frame of the plasmid vector pQE 60 (Qiagen, Germany) at the NcoI-BglII restriction endonuclease sites so that six additional histidine residues were synthesized at the C terminus of the target protein during transla [8]; SECRET, chemokine binding domain [9]. The isolated amino acid sequence corre sponding to the TNF BD protein obtained in this study is underlined.…”