Expression and processing of the canine calicivirus capsid precursor

This study identified and characterized the capsid precursor protein of canine calicivirus (CaCV), an important pathogen causing fatal diarrhea in dogs. Researchers demonstrated that CaCV's ORF2 gene encodes a 75 kDa capsid precursor protein that undergoes proteolytic processing into a mature 57 kDa capsid protein and a 22 kDa N-terminal polypeptide. Using transfection experiments in mammalian cells, the team showed that CaCV's precursor alone was not processed, but was cleaved when co-expressed with the proteinase from feline calicivirus (FCV). Site-directed mutagenesis confirmed the cleavage site at positions 124-125 (Glu-Ser). The findings suggest CaCV likely encodes a similar proteinase in its ORF1 region. This work demonstrates that CaCV shares fundamental molecular mechanisms with related caliciviruses like FCV and San Miguel sea lion virus, and supports classifying CaCV within the Vesivirus genus based on genomic organization and protein processing strategies.

Key findings

• The ORF2 product of canine calicivirus is a 75 kDa capsid precursor protein that is cleaved into a 57 kDa mature capsid protein and a 22 kDa N-terminal polypeptide
• The cleavage occurs at the Glu124-Ser125 site, confirmed by site-directed mutagenesis blocking proteolytic processing when these residues were mutated
• Feline calicivirus proteinase can cross-cleave the CaCV capsid precursor, indicating similar protease specificity and suggesting CaCV encodes a comparable proteinase
• CaCV's capsid precursor processing resembles that of other members of the Vesivirus genus, supporting taxonomic classification alongside FCV and San Miguel sea lion virus