The ORF3a accessory protein in SARS-CoV2 has 73% homology in regard to amino acid sequence when compared to its counterpart in SARS-CoV. The cysteine-rich motif and the tyrosine-based motif were also seen in SARS-CoV but the SGD motif was not and instead, there was an EXD motif in SARS-CoV (hence, the EXD motif was not conserved).

Comparison of Conserved Motifs of ORF3a Protein between SARS-CoV and SARS-CoV2

The conserved motifs of the ORF3a Accessory Protein of SARS-CoV2 play a potential role in the establishment of infection, inducing apoptosis of host cell, as well as the localization of the ORF3a protein in the host cell.


Potential Functions of the Conserved Motifs of the ORF3a protein of SARS-CoV2

Conserved Motifs in proteins can be quite beneficial as they may provide insights into the function and structural properties of the protein. In the case of the ORF3a Protein, three conserved motifs were observed:
- Cysteine-rich motif
- SGD motif
- Tyrosine-based motif

Ohio State University, Columbus

Similar to other accessory proteins, ORF3a plays an important role in the virulence of SARS-CoV2 including affecting the host antiviral response. ORF3a codes for a protein that is made of 274 amino acids and three regions: an ion channel, CBM (Caveolin Binding Motif), and TNF Receptor Associated Factor (TRAF). 

Structure of ORF3a Accessory Protein

Ren, Y., Shu, T., Wu, D. et al. The ORF3a protein of SARS-CoV-2 induces apoptosis in cells. Cell Mol Immunol 17, 881–883 (2020). https://doi.org/10.1038/s41423-020-0485-9

The ORF3a protein of SARS-CoV-2 induces apoptosis in cells

Conserved Motifs of the ORF3a Protein

Co-occurring mutations have been observed between ORF3a and the region encoding the (S) spike glycoprotein and this may indicate some form of relation in the functions of the S protein and the ORF3a protein. One major function of the ORF3a protein seems to be in apoptosis (or “programmed cell death”) of host cells which will be discussed in further nodes.

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