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A number of interactions with host proteins and effects on host cell processes have been described. The SARS-CoV ORF7a protein has been reported to have binding activity to integrin I domains.[6]
It has also been reported to induce apoptosis via a caspase dependent
pathway.[1][7] Also, it contains a motif which has been demonstrated to mediate COPII dependent transport out of the endoplasmic reticulum, and the protein is targeted to the Golgi apparatus.[8]
In SARS-CoV-2, ORF7a protein has been described as an effective interferon antagonist.[3] The SARS-CoV-2 protein may have immunomodulatory effects through interaction with monocytes.[5]
Structural superposition of the Ig domains of ORF8 (blue, PDB: 7JTL[12]) and ORF7a (orange, PDB: 7CI3[5]) illustrating the similarity of their beta-sandwich topologies.
It is thought that ORF8 in SARS-CoV-2, which encodes a protein with a similar Ig-like fold, may be a paralog of ORF7a that originated through gene duplication,[13][14] though some bioinformatics analyses suggest the similarity may be too low to support duplication, which is relatively uncommon in viruses.[15] Immunoglobulin domains are uncommon in coronaviruses; other than the subset of betacoronaviruses with ORF8 and ORF7a, only a small number of bat alphacoronaviruses have been identified as containing likely Ig domains, while they are absent from gammacoronaviruses and deltacoronaviruses.[16][14] The beta and alpha Ig domains may be independent acquisitions, where ORF8 and ORF7a may have been acquired from host proteins.[16]
Many SARS-CoV-2 genomes have been sequenced throughout the COVID-19 pandemic and a number of variations have been reported, including deletion mutations,[17]nonsense mutations (introducing a premature stop codon and truncating the protein),[18] and at least one gene fusion.[19] Recent analyses indicate that the repeated knockout of ORF8 in SARS-CoV-2 through deletion mutations is driven by positive selection, suggesting an adaptive advantage for the virus during human infection. The study showed ORF8 deletions were associated with less severe clinical disease. [20]
^Pekosz A, Schaecher SR, Diamond MS, Fremont DH, Sims AC, Baric RS (2006). "Structure, Expression, and Intracellular Localization of the SARS-CoV Accessory Proteins 7a and 7b". The Nidoviruses. Advances in Experimental Medicine and Biology. Vol. 581. pp. 115–20. doi:10.1007/978-0-387-33012-9_20. ISBN978-0-387-26202-4. PMC7123408. PMID17037516.
^Pekosz, Andrew; Schaecher, Scott R.; Diamond, Michael S.; Fremont, Daved H.; Sims, Amy C.; Baric, Ralph S. (2006). "Structure, Expression, and Intracellular Localization of the SARS-CoV Accessory Proteins 7a and 7b". The Nidoviruses. Advances in Experimental Medicine and Biology. Vol. 581. pp. 115–120. doi:10.1007/978-0-387-33012-9_20. ISBN978-0-387-26202-4. PMC7123408. PMID17037516.
