The 9b accessory protein has two main functions in protein degradation in the mitochondria of the host cell: 
- leads to elongation of the mitochondria by targeting the DRP1 protein
- targets MAVS signalosome (leads to apoptosis)

Relationship between ORF9b Acessory Protein and the Mitochondria of Host cells

The 9b accessory protein facilitates the elongation of the mitochondria by initiating a sequence of events that begin with attaching a small molecule known as ubiquitin (a process known as ubiquitination) to the DRP1 protein (dynamin-like protein) and this essentially tags the DRP1 protein for degradation in the proteasome (protease complex responsible for protein degradation). The elongation of the mitochondria is a factor that may lead to the suppression and potential evasion of the innate response triggered by the host.

Mitochondrial elongation by ORF9b

While the main function of mitochondria is in providing energy for the cell, it also harbors important roles in factors such as cell death (apoptosis) and in the innate antiviral response.

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Grand Valley State University

The 9b accessory protein in SARS-CoV has peculiar membrane-binding functions and is also seen to play a significant role in the suppression of our innate immune response by targeting the mitochondria. Antibodies against the 9b accessory protein were observed in individuals with SARS-CoV. 

Observed Functions of the 9b Accessory Protein (mainly in SARS-CoV)

Shi, C. S., Qi, H. Y., Boularan, C., Huang, N. N., Abu-Asab, M., Shelhamer, J. H., & Kehrl, J. H. (2014). SARS-coronavirus open reading frame-9b suppresses innate immunity by targeting mitochondria and the MAVS/TRAF3/TRAF6 signalosome. The Journal of Immunology, 193(6), 3080-3089.

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