Protein Domain : Non-structural protein NSP8 superfamily, coronavirus IPR037230

Type	Homologous_superfamily
Description	Viral non-structural protein NSP8 is part of the RNA-dependent RNA polymerase (RdRp) complex and forms a heterotetramer consisting of one molecule of NSP7, two copies of NSP8 and one of NSP12 [ ]. NSP8 and NSP7 adopts a hollow cylinder-like structure [, ] in which the dimensions of the central channel and positive electrostatic properties of the cylinder imply that it confers processivity on RdRp [, ]. NSP7 and NSP8 are co-factors for the catalytic NSP12 that play a role in the stabilisation of NSP12 regions involved in RNA binding and are essential for a highly active NSP12 polymerase complex []. It has been demonstrated that NSP8 from human coronavirus 229E acts as an oligo(U)-templated polyadenylyltransferase but also has robust (mono/oligo) adenylate transferase activities []. NSP8 has N-terminal and C-terminal D/ExD/E conserved motifs. The N-terminal motif is critical for RNA polymerase activity as these residues are part of the Mg2-binding active site []. NSP8 has a 'golf club'-like structure composed of a long α-helix N-terminal 'shaft' subdomain and an α/β C-terminal 'head' subdomain consisting of three α-helices and seven β-strands ( ). The seven β-strands form an open-barrel with two antiparallel β-sheets packed orthogonally. More than half the residues in the C-terminal domain are hydrophobic, and the whole domain forms a tight hydrophobic core [ , , ].Together with NSP9, NSP8 suppresses protein integration into the cell membrane, thus, disrupting host immune defenses [ ].The core structure of NSP8 has an α-β(2)-α-β(4)-α-β fold with bifurcated barrel-like β-sheet.
Short Name	NSP8_sf_CoV