| Type: | Family | Name: | Peptidase A6, nodavirus coat protein |
| Description: | Aspartic endopeptidases of vertebrate, fungal and retroviral origin have been characterised []. More recently, aspartic endopeptidases associated with the processing of bacterial type 4 prepilin [] and archaean preflagellin have been described [, ].Structurally, aspartic endopeptidases are bilobal enzymes, each lobe contributing a catalytic Asp residue, with an extended active site cleft localised between the two lobes of the molecule. One lobe has probably evolved from the other through a gene duplication event in the distant past. In modern-day enzymes, although the three-dimensional structures are very similar, the amino acid sequences are more divergent, except for the catalytic site motif, which is very conserved. The presence and position of disulphide bridges are other conserved features of aspartic peptidases.All or most aspartate peptidases are endopeptidases. These enzymes have been assigned into clans (proteins which are evolutionary related), and further sub-divided into families, largely on the basis of their tertiary structure.This group of proteins, which include the Nodavirus coat precusor endopeptidases, are aspartic peptidases that belong to the MEROPS peptidase family A6 (clan AB).Nodaviruses are small, icosahedral viruses, pathogenic to insects and mammals. A virus particle consists of a single virion, within which is packaged two RNA stands, RNA1 and RNA2.Nodavirus coat precursor endopeptidase (also known as protein alpha) is the only protein encoded by RNA2. During the process of virion assembly, this precursor is cleaved into coat proteins beta and gamma. RNA1 encodes two proteins, at least one of which is involved in RNA replication. The relatively uncomplicated nature of their structural protein and RNA constituents make the nodaviruses a good virus model [].The 3D structure of the capsid protein has been determined by X-ray crystallography to 2.8A resolution []. The structure contains a beta-barreldomain, with a prominent protrusion composed largely of beta-sheet. This protrusion, together with similar protrusions from neighbouring subunits,forms a prominent trigonal pyramid with quasi-3-fold symmetry []. Twoalpha-helices extend toward the interior of the particle []. | Short Name: | Peptidase_A6 |
