Sequence analysis of haemagglutinin gene of camelpox viruses shows deletion leading to frameshift: Circulation of diverse clusters among camelpox viruses

Abstract

Orthopoxviruses (OPVs) have broad host range infecting a variety of species along with gene-specific determinants. Several genes including haemagglutinin (HA) are used for differentiation of OPVs. Among poxviruses, OPVs are sole members encoding HA protein as part of extracellular enveloped virion membrane. Camelpox virus (CMLV) causes an important contagious disease affecting mainly young camels, endemic to Indian subcontinent, Africa and the Middle East. This study describes the sequence features and phylogenetic analysis of HA gene (homologue of VACV A56R) of Indian CMLV isolates. Comparative analysis of CMLV HA gene revealed conserved nature within CMLVs but considerable variability was observed between various species of OPVs. Most Indian CMLV isolates showed 99.5%-100% and 96.3%-100% identity, at nucleotide (nt) and amino acid (aa) levels respectively, among themselves and with CMLV-M96 strain. Importantly, Indian CMLV strains along with CMLV-M96 showed deletion of seven nucleotides resulting in frameshift mutation at C-terminus of HA protein. Phylogenetic analysis displayed distinct clustering among CMLVs which might point to the circulation of diverse CMLV strains in nature. Despite different host specificity of OPVs, comparative sequence analysis of HA protein showed highly conserved N-terminal Ig V-set functional domain with tandem repeats. Understanding of molecular diversity of CMLVs and structural domains of HA protein will help in the elucidation of molecular mechanisms for immune evasion and design of novel antivirals for OPVs.

Keywords: camelpox virus; extracellular enveloped virion; haemagglutinin; immunoglobulin V-set domain; orthopoxviruses.