Table 4.
Structure and function of accessory proteins.
| Structure solved (SARS-CoV-2) | Structure solved (SARS-CoV) | Description of the structure | Function | Functional name | |
|---|---|---|---|---|---|
| 3a | Solved for SARS-CoV-2157
(Cryo-EM Struture) PDB: 6XDC |
Not solved | It is an ion channel with 275 amino acid residues (274 amino acid residues in SARS-CoV). It is an O-glycosylated protein with three transmembrane helices followed by cytosolic domains with multiple β-strands per protomer chain and an N-terminal ectodomain and a C-terminal endodomain in both intracellular and plasma membranes.162,163 | Interactions with some structural proteins (S, M and E) and observed inducing apoptosis in vitro 164 - 166 | Hole borer |
| 3b | Not solved | Not solved | It is 154 amino acids long for SARS-CoV (151 for SARS-CoV-2). 1 | It induces apoptosis and necrosis, and hinders antiviral innate immune response. 167 - 169 | Immune modulator |
| 6 | Not solved | Not solved | It is 63 amino acids long in SARS-CoV (61 for SARS-CoV-2). 1 | It suppress IFN induction and IFN signaling pathway.169,170 | Type 1 interferon antagonist |
| 7a | Solved for SARS-CoV-2 (X-Ray Crystallography) PDB:7Ci3 |
Solved for SARS-CoV 171 (X-Ray Diffraction) PDB: 1XAK | It is a type I transmembrane protein with 121 amino acids (122 for SARS-CoV that contain 15-amino-acid N-terminal signal peptide sequence, an 81-amino-acid luminal domain, a 21-amino-acid transmembrane domain and a short C-terminal tail. 171 | It induces apoptosis, inhibits cellular protein synthesis and arrests cell cycle at the GO/G1 phase. 172 - 174 | Immune evador |
| 7b | Not solved | Not solved | It is an integral membrane protein with 44 amino acids (43 for SARS-CoV-2). 1 | Immune evador | |
| 8 | Solved for SARS-CoV-2 (X-Ray Diffraction) PDB: 7JTL | 8a—Not solved | It is a 39-amino-acid-long polypeptide in which residues 1-35 are identical to the N-terminal of 8ab. | It is found to enhance replication in some studies and shows interaction with other structural proteins.175,176 ORF8 is not splitted into ORF 8a and 8b and have amino acids length of 121 in SARS-CoV-2. 1 | Immune modulator |
| 8b—Not solved | It is a 84-amino-acid-long polypeptide and residues 9-84 are identical to the C terminal of 8ab. | ||||
| 9b | Solved for SARS-CoV-2 (X-Ray Crystallography) PDB: 6Z4U. | Solved for SARS-CoV 177 (X-Ray Diffraction) PDB: 2CME | It is 70 amino acids long protein (73 in case of SARS-CoV-2). It contains a novel dimeric fold having β strands like structure with an amphipathic surface and a central hydrophobic cavity. 177 | It shows interaction with some nonstructural proteins, and incorporates into mature virions. 178 - 180 | Internal N protein |
| 10 | Not solved | Not found | It is a 38-amino-acid-long protein. It has one potential TM domain. Presence of one α-helix and two β-strands and β-α-β motif with a β-molecular recognition feature occurring in the first β-strand is revealed through the prediction of secondary structural elements of this protein | It has potential immune modulatory role. | Mystery protein |
Abbreviations: IFN, interferon; ORF, Open Reading Frames; TM, transmembrane.