Table 1.
Structural proteins, genes, and their potential functions in MERS-CoV.
| Proteins | Coding genes | Functions and/or effect on the cellular response of the host |
|---|---|---|
| Spike (S) protein | ORF2 | Viral entry, receptor binding, membrane fusion |
| Envelope (E) protein | ORF6 | Virion assembly; putative ion channel activity and is involved in viral budding and release; potential B cell epitopes |
| Membrane (M) protein | ORF7 | Virion assembly—the formation of the viral envelope and viral core by interacting with the N protein; IFN antagonism |
| Nucleocapsid (N) protein | ORF8a | Main component of the nucleocapsid structure—essential for viral replication and assembly, and post-translational modification Modulating the host’s initial innate immune response |
| AP 3 | ORF3 | Viral replication and pathogenesis |
| AP 4a | ORF4a | Viral replication, IFN antagonism, protein kinase R (PKR) antagonism |
| AP 4b | ORF4b | IFN antagonism, nuclear factor kappa B (NF-κB) inhibition |
| AP 5 | ORF5 | IFN antagonist, modulation of NF-κB-mediated inflammation |
| Nsp1-coding region | nsp1 | Specific recognition of viral RNA that is required for efficient viral replication; possibly interacts with cyclophilins and is thought to be a major virulence factor because it suppresses protein synthesis through the degradation of host mRNA |
| Papain-like protease (PLpro) | nsp3 | PLpro is responsible for the cleavage at positions 1–3 to develop three nonstructural proteins (nsps); two selected sites (G720 and R911) were detected in the protease domain; viral replication; membrane proliferation; IFN antagonist; deubiquitination; putative dephosphorylation of Appr-1″-p, a side product of cellular tRNA splicing, to ADP-ribose |
| Transmembrane domain | nsp4 | Viral replication; membrane proliferation |
| Main, chymotrypsin-like, or 3C-like protease (3CLpro) | nsp5 | Viral survival—proteolytic processing of the replicative polyprotein at specific sites and 3CLpro cleaves the remaining positions 4–16 key functional enzymes, such as replicase and helicase |
| Transmembrane domain | nsp6 | Membrane proliferation; interaction with nsp3 and nsp4 |
| Primase | nsp8 | Primase activity |
| Unknown | nsp9 | Nsp9 is an essential protein dimer with RNA/DNA binding activity in SARS-CoV |
| Unknown | nsp10 | Membrane proliferation—regulating 2′-O-MTase activity |
| RNA-dependent RNA polymerase | nsp12 | Viral replication and transcription |
| Superfamily 1 helicase | nsp13 | Viral replication; affects tropism and virulence |
| 3′-to-5′exonuclease | nsp14 | Viral replication—exoribonuclease activity |
| N7-methyltransferase Nidoviral endoribonuclease specific for U | nsp15 | Viral replication—exoribonuclease activity |
| S-adenosylmethionine-dependent ribose 2′-O-methyltransferase | nsp16 | Methyltransferase inhibition; viral replication; IFN antagonism |