Peptidase C24, Calicivirus polyprotein ORF 1

Peptidase C24, Calicivirus polyprotein ORF 1(InterPro Protein Domain record)

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Peptidase C24, Calicivirus polyprotein ORF 1

InterPro Protein Domain record

description http://metadb.riken.jp/db/SciNetS_rib124i/prib124u1i

In the MEROPS database peptidases and peptidase homologues are grouped into clans and families. Clans are groups of families for which there is evidence of common ancestry based on a common structural fold:<ul> <li>Each clan is identified with two letters, the first representing the catalytic type of the families included in the clan (with the letter 'P' being used for a clan containing families of more than one of the catalytic types serine, threonine and cysteine). Some families cannot yet be assigned to clans, and when a formal assignment is required, such a family is described as belonging to clan A-, C-, M-, N-, S-, T- or U-, according to the catalytic type. Some clans are divided into subclans because there is evidence of a very ancient divergence within the clan, for example MA(E), the gluzincins, and MA(M), the metzincins.</li><li>Peptidase families are grouped by their catalytic type, the first character representing the catalytic type: A, aspartic; C, cysteine; G, glutamic acid; M, metallo; N, asparagine; S, serine; T, threonine; and U, unknown. The serine, threonine and cysteine peptidases utilise the amino acid as a nucleophile and form an acyl intermediate - these peptidases can also readily act as transferases. In the case of aspartic, glutamic and metallopeptidases, the nucleophile is an activated water molecule. In the case of the asparagine endopeptidases, the nucleophile is asparagine and all are self-processing endopeptidases. </li></ul>In many instances the structural protein fold that characterises the clan or family may have lost its catalytic activity, yet retain its function in protein recognition and binding. 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 [<cite idref="PUB00011704"/>]. 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 [<cite idref="PUB00003528"/>]; while ORF1 encodes a non-structural polypeptide, which has RNA helicase, cysteineprotease and RNA polymerase activity. The regions of the polyprotein inwhich 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 PAprotease clan, constitute family C24 of the cysteine proteases (proteasesfrom SRSVs belong to the C37 family). As mentioned above, the proteaseactivity resides within a polyprotein. The enzyme cleaves the polyproteinat sites N-terminal to itself, liberating the polyprotein helicase.

label http://www.w3.org/2000/01/rdf-schema#label