Structure of FCV capsid protein, VP1. A Schematic representation of FCV capsid precursor protein, which is cleaved into mature proteins LC and VP1. The figure shows capsid precursor protein antigenic regions (A–F) and the VP1 structural domains (NTA, S, P1 and P2). B Ribbon representation of the VP1 protein structure (Protein Data Bank [PDB] accession number 3M8L). The NTA, S domain, P1 and P2 subdomains are indicated. C Coomassie blue stained SDS-10% PAGE of H5 insect cell extracts infected with recombinant baculovirus expressing VP1 protein. Molecular weight markers (MW) are given on the left (× 103 Da). D Electron micrograph of a negatively stained sample of purified FCV VLPs. Bar, 100 nm.