| Type: | Domain | Name: | Peptidase C24, Calicivirus polyprotein Orf1 |
| Description: | Cysteine peptidases have characteristic molecular topologies, which can be seen not only in their three-dimensional structures, but commonly also in the two-dimensional structures. These are peptidases in which the nucleophile is the sulphydryl group of a cysteine residue. Cysteine proteases are divided into clans (proteins which are evolutionary related), and further sub-divided into families, on the basis of the architecture of their catalytic dyad or triad []. The two signatures that defines this group of calivirus polyproteins identify a cysteine peptidase signature that belongs to MEROPS peptidase family C24 (clan PA(C)). Caliciviruses are positive-stranded ssRNA viruses that cause gastroenteritis. The calicivirus genome contains two open reading frames, ORF1 and ORF2. ORF2 encodes a structural protein []; while ORF1 encodes a non-structural polypeptide, which has RNA helicase, cysteineprotease and RNA polymerase activity. The regions of the polyprotein in which these activities lie are similar to proteins produced by the picornaviruses. Two different families of caliciviruses can be distinguished on the basis of sequence similarity, namely those classified as small round structured viruses (SRSVs) and those classed as non-SRSVs.Calicivirus proteases from the non-SRSV group, which are members of the PA protease clan, constitute family C24 of the cysteine proteases (proteasesfrom SRSVs belong to the C37 family). As mentioned above, the protease activity resides within a polyprotein. The enzyme cleaves the polyproteinat sites N-terminal to itself, liberating the polyprotein helicase. | Short Name: | Peptidase_C24 |
