Table 2.
Comparing Protein Differences in Coronavirus
| Types of Protein | SARS-CoV | MERS-CoV | SARS-CoV-2 |
|---|---|---|---|
| Spike protein (S) | S protein can bind to ACE2 directly, and the binding sequence site is highly consistent with SARS-CoV-2.60 | The core structure of the S2 gene of SARS-CoV is very similar, but the structure of the receptor-binding motif is quite different, so its receptor is dipeptidyl peptidase.57 | Compared with SARS-CoV, the receptor-binding domain sequence homology of S protein is 76%.60 Its S protein also participates in the process of virus invasion by binding to the ACE2 receptor.61 |
| Envelope protein (E) | E protein acts as an ion channel in the form of a pentamer.58 | Control virion assembly, deletion mutants lose pathogenicity.58,62 | Compared with SARS-CoV, the sequence homology of E protein is as high as 95%.60 It is suggested that the functional diversity of E protein in the process of coronavirus replication and pathogenesis. |
| Membrane protein (M) | M protein is only expressed in the endoplasmic reticulum and Golgi matrix. Its conserved domain participates in the process of virus assembly and budding through protein-protein interaction.53 | Control virion assembly.63 | Compared with SARS-CoV, the homology is as high as 91%.60 The specific function is not clear. |
| Nucleocapsid protein (N) | Serum cross-reaction can occur through N protein.64 | It can fold the coronavirus genome into a spiral ribonucleoprotein (RNP). At the same time, it can also enhance the efficiency of virus transcription and assembly.65 | Compared with SARS-CoV, the homology is as high as 94%.60 It is possible to recognize the N protein of SARS-CoV in the COVID-19 patient’s serum and this can be used for clinical detection of asymptomatic patients. |
| Open reading frames (ORFs) ORF3b | ORF3b protein is meaningless in the process of SARS-CoV replication.51 It can inhibit the IFN-β signal pathway and does not depend on protein nuclear localization.60 | Nonstructural protein, no difference. | A specific protein with four helical structures was found in the fragment of ORF3b protein, and there was no homologous sequence with SARS-CoV.60 |
| ORF8 | ORF8 protein can activate intracellular stress signals and cause an NOD-like receptor protein 3 (NLRP3) inflammatory response.66 | Nonstructural protein, no difference. | Compared with SARS-CoV, ORF8 has a 20% homology, which is the lowest homologous protein but can mediate the downregulation of host cell MHC-II.67 |