Structural accessory protein ORF7b of Severe Acute Respiratory Syndrome coronavirus 2 and similar proteins
This group contains the ORF7b, also called NS7b, of Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2), also known as 2019-nCoV, and a bat coronavirus (BatCoV RaTG13), which was previously detected in Rhinolophus affinis from China's Yunnan province and showed high sequence identity to SARS-CoV-2. ORF7b/NS7b from betacoronavirus in the B lineage are not related to NS7b proteins from other betacoronavirus lineages. There are five essential genes in CoVs that result in the following gene products: Spike (S) protein, Membrane (M) glycoprotein, Nucleocapsid (N), Envelope (E) protein, and the ORF1ab (a large polyprotein known as replicase/protease); all required to produce a structurally complete viral particle. In addition, SARS coronavirus contains a number of open reading frames that code for a total of eight accessory proteins, namely ORFs 3a, 3b, 6, 7a, 7b, 8a, 8b, and 9b. These ORFs are specific for SARS-CoV and do not show significant homology to accessory proteins of other coronaviruses. The SARS-CoV ORF7b protein is a highly hydrophobic 43 amino acid protein which is homologous to an accessory but structural component of SARS-CoV virion. While ORF7b is packaged into virions, it is not required for the virus budding process, as gene 7 deletion viruses replicate efficiently in vitro and in vivo. Moreover, ORF7b possesses a transmembrane helical domain (TMD), between 9-29 amino acid residues, is necessary for its Golgi complex localization, as replacing it with the TMD from the human endoprotease furin results in aberrant localization.
Jiyao W et al.(2023). "The conserved domain database in 2023.",