Smoking Upregulates Angiotensin-Converting Enzyme-2 Receptor: A Potential Adhesion Site for Novel Coronavirus SARS-CoV-2 (Covid-19)

Brake, Samuel James; Barnsley, Kathryn; Lu, Wenying; McAlinden, Kielan Darcy; Eapen, Mathew Suji; Sohal, Sukhwinder Singh

Fatality rates are given as the percentage of the defined group with confirmed Covid-19 that died, and therefore will not add up to 100%. The Table 1 was adapted from Coronavirus Disease (Covid- 19) Research and Statistics [15] . The term "coronaviruses" arose from their crown-like appearance when imaged, the Latin for crown being corona. The distinguishing crown-like feature of coronaviruses is attributed to the presence of large type 1 transmembrane spike (S) glycoproteins. This heavily glycosylated cell surface protein contains two distinct functional domains (S1 and S2) which are thought to mediate host cell entry by the virus. The S1 domain contains the angiotensin-converting enzyme-2 (ACE2) receptor-binding domain and is responsible for first stage host cell entry [16] . The S2 domain facilitates fusion between cell and virus membrane, required for cellular infiltration [17] . S proteins are enzymatically modified, exposing the fusion site for cellular adhesion. This is achieved through cleavage by cellular proteases, mediated by protein convertase called "furin" [17, 18] . Furin is expressed significantly in the lungs, and respiratory viruses also utilize this system to convert their surface proteins [17] . Although the S protein cleavage site is less observed in coronavirus with similar genomic sequence [17] , it is essential to note that more pathogenic influenza viruses share similar cleavage sites [19] .