ORF9b
| Betacoronavirus lipid binding protein | |||||||||
|---|---|---|---|---|---|---|---|---|---|
 The X-ray crystallography structure of the SARS-CoV ORF9b protein dimer, showing the lipid molecule in the central cavity (yellow). From PDB: 2CME.[1] | |||||||||
| Identifiers | |||||||||
| Symbol | bCoV_lipid_BD | ||||||||
| Pfam | PF09399 | ||||||||
| InterPro | IPR018542 | ||||||||
| |||||||||
ORF9b (formerly sometimes called ORF13) is a
amino acid residues long in SARS-CoV[2][3] and 98 in SARS-CoV-2,[4] in both cases forming a protein dimer
.
Nomenclature
There has been inconsistency in the nomenclature used for this gene in the scientific literature. In some work on SARS-CoV, it has been referred to as ORF13. It has also sometimes been referred to as ORF9a, resulting in a downstream ORF of 76
codons in SARS-CoV, also overlapping with the N gene, being designated ORF9b. The recommended nomenclature refers to the longer ORF as 9b and the downstream, shorter ORF as ORF9c.[5]
Structure
The ORF9b protein is 97
hydrophobic cavity in the center that binds lipids.[2][3][4] The lipid-binding cavity may serve as an unusual mechanism for anchoring the protein to membranes.[1]
A fragment of the SARS-CoV-2 ORF9b protein has been structurally characterized in a
Tom70 in which ORF9b forms an alpha helix rather than the beta-sheet structure observed in isolation.[6] This fold switching behavior is also consistent with bioinformatics predictions and may also occur for the SARS-CoV homolog.[7]
Expression and localization
ORF9b is one of two
protein-coding gene.[9]
In SARS-CoV, the protein is
mitochondrial membrane.[4]
Function
The function of the ORF9b protein is not well characterized. It is not essential for viral replication.[2]
Viral protein interactions
The ORF9b protein has been reported to interact with a number of other viral proteins, including
Host cell effects
The ORF9b protein may be involved in modulating the host's
