Parnad Basu, Amity University Kolkata
The pandemic caused by COVID-19 is continuing still. The causative viral pathogen of COVID-19 is SARS-CoV-2 (severe acute respiratory syndrome coronavirus 2). This SARS-CoV-2 actually belongs to the β coronavirus genus along with SARS-CoV (severe acute respiratory syndrome coronavirus) and MERS-CoV (middle east respiratory syndrome coronavirus). Although SARS-CoV-2 targets the respiratory tract first, it has been in other human organs as well (e.g., lungs, pharynx, heart, liver, brain, kidneys, and digestive system organs). SARS-CoV and SARS-CoV-2 share more than 75% genetic identity and previous studies have also shown that a cellular receptor called ACE2 binds with both of them.
The ACE2 cellular receptor is not expressed in every human organ in the same quantity. In addition to that, some recent studies have disclosed that more than one neutralizing human antibodies can bind to SARS-CoV-2 spike glycoproteins but not RBD (receptor binding domain). To shed light on that a group of scientists used TAP (tandem affinity purification)-MS (mass spectrometry) and found out about AXL (tyrosine-protein kinase receptor UFO). AXL overexpression was seen to promote viral entry as efficiently as ACE2 in the case of HEK293T cells.
We already knew that SARS-CoV, SARS-CoV-2, and MERS-CoV belong to the same genus of the coronavirus. However, this study suggests that unlike those past two coronaviruses, SARS-CoV-2 can and does use both ACE2 and AXL receptors to enter a human body. AXL receptor uses ‘apoptotic mimicry’ to increase the transduction efficiencies of lentiviral vectors pseudo-typed with several types of envelope proteins. And then AXL receptor promotes the entry of SARS-CoV-2 into human pulmonary epithelial cells. Other than that, AXL is present in almost all human organs which makes it much more useful. With further studies on the AXL receptor, the development of therapeutic solutions for COVID-19 will be much easier.
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Reference: AXL is a candidate receptor for SARS-CoV-2 that promotes infection of pulmonary and bronchial epithelial cells. Lu et al.: https://doi.org/10.1038/s41422-020-00460-y
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