ORF7b

This accessory protein is an integral transmembrane protein and it localizes in the cis- and trans- Golgi. MSARS-CoV-2 ORF7b is 81 % identical to  SARS-CoV-1 ORF7b. All substitutions are found in the terminals, being the transmembrane helix fully conserved.

Narrative

ORF7b is a small accessory protein expressed in SARS-CoV-1 and SARS-CoV-2 infected cells with no sequence homology with other viral proteins (Schaecher, Mackenzie, and Pekosz 2007). It is translated from a bicistronic open reading frame and encoded in the subgenomic RNA 7 and translated by ribosome leaky scanning (Schaecher, Mackenzie, and Pekosz 2007). Like other accessory proteins, ORF7b is incorporated in viral particles and detected in purified virions (Schaecher, Mackenzie, and Pekosz 2007). ORF7b is an integral transmembrane protein and it localizes in the cis- and trans- Golgi (Schaecher, Diamond, and Pekosz 2008). Deletion of gene 7 does not affect replication kinetics in vitro, suggesting that ORF7b is not essential for virus replication (Pekosz et al. 2006).

Structural analysis and comparison with SARS-CoV-1 ORF7b – SARS-CoV-1 ORF7b is a small protein of 44 amino acids with a transmembrane domain (TMD) of 22 residues (Schaecher, Diamond, and Pekosz 2008). Mutations in the TMD affect ORF7b cellular localization (Schaecher, Diamond, and Pekosz 2008). Alanine scanning experiments, identified that residues 13-15 and 19-22 are critical for ORF7b retention in the Golgi complex. SARS-CoV-2 ORF7b is 81% identical to SARS-CoV-1 ORF7b. All substitutions are found in the terminals, meaning the TMD is fully conserved.