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.
Highlights
Chemokines form a large family of chemoattractant cytokines with low molecular weight (~7-14 kDa) and their sequence similarity range from 20 to 90%
Our results suggest that SECRET should be included into the family of poxviral type II chemokinebinding proteins and that it might have been evolved from the virus CC-chemokine binding protein (vCCI)-like predecessor protein
Using I-TASSER web-server [11], which was shown to be the best server for predicting spatial structures of proteins according to results of CASP7 (CASP - Critical Assessment of protein Structure Prediction) and CASP8 competitions [11,12], we obtained the model of Variola virus (VARV)-CrmB SECRET domain
Summary
Chemokines form a large family of chemoattractant cytokines with low molecular weight (~7-14 kDa) and their sequence similarity range from 20 to 90%. Through binding to cell surface or intercellular matrix glycosaminoglycans (GAGs) chemokines form chemotactic gradient attracting leukocytes to the sites of injury and inflammation. 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 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
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