Function
The non-structural protein nsp9 contains 113 amino acids[1] and is encoded on the ORF1a[2].
The SARS-CoV nsp9 has been shown to bind to RNA and DNA but preferably to ssRNA and may interact with the replication complex (consisting of nsp7, nsp8 and nsp12). The SARS-CoV-2 nsp9 interactome suggests various potential functions in viral replication, regulating nuclear transport, inhibition of host cell transcription, host shut off or as a complicating factor during pathogenesis[3].
Disease
The global COVID-19 pandemic, which started in 2019, is caused by the SARS-CoV-2.
Structure
The protein structure has an unusual fold, so far only found within coronaviruses. It consists of seven β-sheets and one α-helix at the C-terminus. The β1-β7 fold to form a β-barrel structure. Half of β7 additionally forms a twisted β-hairpin with β6, interacting with the C-terminus. The extended loops connecting the β-strands are directed outward, of which β2-3 and β3-4 are glycine rich, positively charged and might play a role in RNA binding. The conserved GxxxG motif is important for the forming of a nsp9 homodimer[4].
Nsp9 has been shown to be able to bind to rhinoviral 3C protease sequence (LEVL) close to the dimer binding site[4].
Variations
Compared to the amino acid sequence of SARS-CoV, the SARS-CoV-2 sequence of nsp9 has three amino acid substitutions, resulting in a sequence identity of 97.3%[1].
See also
Coronavirus_Disease 2019 (COVID-19)
SARS-CoV-2_virus_proteins
COVID-19 AlphaFold2 Models