Table 1.
Non-structural proteins of SARS CoV-2 and their function.
| NSP | Amino acid (aa) | Functiona | Accession number | Reference |
|---|---|---|---|---|
| NSP1 (leader proteins) | 180 aa | Blocks host innate immune response and suppresses IFN signalling by binding to host 40S ribosome, halting translation and thereby selectively degrading host mRNA. | YP_009725297.1 | [20] |
| NSP2 | 638 aa | Found conserved in another coronavirus, SARC-CoV. This protein binds with prohibitin 1(PHB1) and prohibitin 2 (PHB2) present in host, and thus is responsible for disrupting the host cell environment. | YP_009725298.1 | [33] |
| NSP3 | 1945 aa | The largest protein encoded by coronavirus, it is around 200 KDa in size and a papain-like proteinase protein. This protein also eases release of NSP1, NSP2, and NSP3 from the N-terminal region. NSP3 shuts down host enzymes called PARPs, which prevent viruses from replicating. | YP_009725299.1 | [34,35] |
| NSP4 | 500 aa | Accommodates transmembrane domain and interacts with NSP3 as well as host proteins and assists reorganization of SARS CoV membrane. However, both NSP4 and NSP3 are involved together for their role in viral replication. | YP_009725300.1 | [36] |
| NSP5 | 306 aa | The main protease promoting cytokine expression and cleavage of viral polyprotein. SARS CoV-2 NSP5 is highly homologous to SARS NSP5 (identity, 96%; similarity, 98%). | YP_009725301.1 | [37] |
| NSP6 | 290 aa | This, similarly to other CoVs, presents putative trans-membrane helices and interacts with NSP3 and NSP4. This protein is involved in generation of autophagosome from the endoplasmic reticulum and enable assembly of replicase proteins. | YP_009725302.1 | [38,39] |
| NSP7 and NSP8 | 83 aa | Both NSP7 and NSP8 form a heterodimer that efficiently performs de novo initiation and primer extension. Both NSP7 and NSP8 are found conserved among 2019-nCoV, BetaCoV_RaTG, and BatSARS-like Cov. | NSP7, YP_009725303.1 | [40,41] |
| 198 aa | NSP8, YP_009725304.1 | |||
| NSP9 | 113 aa | Suggested involvement in viral replication and virulence. | YP_009725305.1 | [42] |
| NSP10 | 139 aa | Previous studies of SARS coronavirus demonstrate that NSP10 interacts and stimulates activity of NSP14 [S-adenosylmethionine (SAM)-dependent (guanine-N7) methyl transferase (N7-MTase)]. Additionally, NSP10 also has a crucial role in activating NSP16 (2′-O-methyltransferase). | YP_009725306.1 | [43,44] |
| NSP11 | 13 aa | Function is still unknown. | YP_009725312.1 | [20] |
| NSP12 | 932 aa | RNA dependent RNA polymerase (RdRp), along with cofactors NSP7 and NSP8, assists in coping viral RNA. Current studies suggest that SARS-CoV-2 NSP12 is almost identical to that of the SARS-CoV (identity, 96%; similarity, 98%). | YP_009725307.1 | [45] |
| NSP13 | 601 aa | A helicase enzyme responsible for unwinding viral genome. As reported previously, the overall structure of SARS-CoV-2 NSP13 is composed of five domains giving a triangular pyramid shape similar to SARS and MERS-Nsp13. | YP_009725308.1 | [46] |
| NSP14 | 527 aa | Current reports suggest it is a proofreading protein with 3’ to 5’ exoribonuclease (NSP14-ExoN). This activity is an important factor of both viral replication and recombination. | YP_009725309.1 | [47] |
| NSP15 | 346 aa | It has been characterized as RNA uridylate-specific endoribonuclease carrying catalytic domain at C-terminal. The NSP15 protein prevents uncovering of virus within host system. This is achieved by degrading the viral polyuridine sequences. | YP_009725310.1 | [48] |
| NSP16 | 298 aa | It is a N7-GpppA-specific, S-adenosyl-l-methionine (SAM)-dependent, 2’-O-MTase and is activated by binding to NSP10. NSP16-NSP10 complex cap viral mRNA transcripts protecting it from degradation by 5′-exoribonucleases, promote efficient translation and assist host innate immunity surveillance. | YP_009725311.1 | [49,50] |
a
Note: The functions of NSPs are reported for SARS-CoV and are considered to be similar in SARS-CoV-2.