Species-specific differences in the structure of orthopoxvirus complement-binding protein.

Vaccinia virus complement-binding protein (VCP) is secreted from the cells infected with the virus and controls the complement activation reactions. This protein contains four short consensus repeats (SCR), typical of the protein family of complement activation regulators. Organization of the VCP genes/proteins of orthopoxviruses-monkeypox (MPV), variola, cowpox and vaccinia viruses-and their cellular homologues (DAF and C4BP) were studied comparatively. For this purpose, VCP genes of three MPV strains were sequenced. VCP gene sequences of other human-pathogenic orthopoxvirus species and strains determined earlier were involved in the analysis. It has been demonstrated that a premature termination of the MPV VCP open reading frame results in a truncated protein sequence carrying a deletion of the C-terminal SCR4. This is an essential distinction of MPV from other orthopoxvirus species.