In regards to amino acid sequence and composition of proteins, SARS-CoV2 bears many resemblances and similarities with SARS-CoV but there are certainly significant differences as well:
- The 8a accessory protein is absent in SARS-CoV2 but is present in other SARS-CoV.
- The 8b accessory protein’s amino acid sequences is longer in SARS-CoV2 with 121 amino acids compared to the 84 amino acids in other SARS-CoV.
- The 3b accessory protein amino acid sequence is considerably shorter in SARS-CoV2 with just 22 amino acids compared to the 154 amino acids seen in other SARS-CoV.


Amino Acid Differences of Accessory Proteins between Sars-CoV2 and SARS-CoV

The ORF coding the 9b accessory protein is present in the Nucleocapsid gene and is comprised of 98 amino acids. While the function of the 9b accessory protein in SARS-CoV2 is not exactly known, a relative idea of its function can be obtained by understanding its role in SARS-CoV as the 9b sequence is heavily conserved in other SARS isolates (indicating that it probably has a very similar function). the 9b sequence is heavily conserved in other SARS isolates.

9b Accessory Protein of SARS-CoV2

Similar to the ORF 9b protein, the function of the ORF14 accessory protein is not exactly known but it is believed to play a potential role in the interaction between the host cells and the virus. This protein has been seen in SARS-CoV2, SARS-CoV, and SARS-like coronavirus Rp3 (a bat coronavirus). 


ORF14 Accessory Protein of SARS-CoV2

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

Apoptosis, which is essentially cell death that is triggered by certain factors, is an important mechanism in the antiviral immune response as it allows the killing of infected cells which aids in limiting and controlling the infection as well as playing a regulatory role in inflammation. Multiple accessory proteins seem to affect apoptosis of host cells and contribute to viral pathogenesis by doing so, making apoptosis an overlapping and overarching concept regarding accessory protein of SARS-CoV2.

Introduction to Apoptosis

Accessory proteins play important roles as virulence factors affecting pathogenicity, release, and stability of SARS-CoV2 and aid in infection, replication, and transmission of the virus between individuals. The SARS-CoV2 accessory proteins are 3a, 3b, p6, 7a, 7b, 8b, 9b, and ORF14.

Ohio State University, Columbus

Kenyon College

SARS-CoV-2 is comprised of four main structural components: the spike glycoprotein (S), the small envelope glycoprotein (E), the membrane glycoprotein (M), and the nucleocapsid protein (N). There are also several accesory proteins. 

Structure of SARS-CoV-2

BARUAH, C., DEVI, P., & SHARMA, D. K.. (2020). Sequence Analysis and Structure Prediction of SARS-CoV-2 Accessory Proteins 9b and ORF14: Evolutionary Analysis Indicates Close Relatedness to Bat Coronavirus (Version 1). ChemRxiv. https://doi.org/10.26434/chemrxiv.12424958.v1

Sequence Analysis and Structure Prediction of SARS-CoV-2 Accessory
Proteins 9b and ORF14: Evolutionary Analysis Indicates Close
Relatedness to Bat Coronavirus

This diagram shows a labeled COVID 19 virus. 

Diagram of Virology of COVID 19 virus

The spike glycoprotein (S) is responsible for attachment between the virus and a cell-surface receptor, leading to the fusion of virus to the cell membrane. This membrane-fusion activity can only occur with the proteolytic cleavage of the S glycoprotein into S1 and S2 subunits, which continue to remain associated with one another after cleavage. 


Spike glycoprotein (S)

Accessory Proteins of SARS-CoV2

The nucleocapsid protein (N) is bound to the viral RNA within a coronavirus particle. The N protein plays important roles in viral transcription and replication, which are parts of the viral life cycle. 

Learn Before

Related

Learn After