Unlocking the secrets of Feline calicivirus: advances in structural and nonstructural proteins and its role as a key model for other Caliciviruses

Figures

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  Fig. 1. (A) Phylogenetic relationships in the family Caliciviridae(B) FCV viral structure is depicted schematically. Both the capsid region F and a conserved section of E5’HVR were shown to have linear, non-neutralizing epitopes. Additionally, E5’HVR was found to contain linear, neutralizing epitopes, as shown by the red circles in the figure. VPg stands for virus protein. The NTR stands for the non-translated region. The abbreviation “NTPas” stands for nucleoside-triphosphatase. LC stands for capsid leader. HVR stands for hypervariable region. (C) Analysis of the genomic structure of FCV. Open reading frames (ORFs) 1–3, subgenomic RNA, antigenic regions (A–F) of the VP1 capsid precursor protein, and the structural domains of the VP1 protein are all included in the illustration. Whereas red numbers show the locations of amino acids in ORF2, black numerals indicate the locations of nucleotides in the viral genome. The blue triangle represents the NS6/7 cleavage sites. The terms LC, HVR, RdRp, gRNA, NTA, and S domain denote the capsid protein leader, the N-terminal arm, the hypervariable region, and the shell domain, respectively

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  Fig. 2. Lifecycle of FCV. Following receptor engagement, the genome is released by clathrin-mediated endocytosis. The 5′ VPg facilitates the translation of non-structural proteins by interacting with the translational machinery. Antigenomic RNA is transcribed by the viral RNA-dependent RNA polymerase (RDRP) and then used to generate genomic RNA. The infectious virions that are discharged from cells and induce cell lysis are made up of structural proteins and RNA

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  Fig. 3. Schematic representation of VP2 facilitating RNA genome release in caliciviruses [26]. By attaching itself on the host cell membrane’s fJAM-A, FCV penetrates early endosomes through clathrin-mediated endocytosis. The gRNA enters the cytoplasm and multiplies there after being released via perforations in the early endosome membrane made by VP2. In late endosomes, the viral capsid is broken down