Figure 5: SARS-CoV-2 virus life cycle
(A) SARS-CoV-2 binds with host cell ACE2 receptor resulting in fusion, either (B1) endocytosis or (B2) priming cleavage by TMPRSS2; shedded ACE2 also augments viral entry by either activated ADAM17 or TMPRSS2. (B1a) Endocytosed virus S protein is also cleaved by cathepsin L; (C) Virus RNA genome is liberated into cytoplasm and (D) translation into polypeptides takes place into endoplasmic reticulum derived double membrane vesicles; (E) Polyproteins are cleaved into NSPs; (F) Translation of structural proteins and RNA replication; (G) Trafficking of newly synthesized proteins and RNA from endoplasmic reticulum to Golgi body; (H) Packaging of virion in the budding vesicle; (I) Mature virus releases via exocytosis; (J) SARS-CoV-2 antigens presentation to antigen presenting cells via MHCs / HLAs; (K) Stimulated antigen presenting cells releases cytokines to enhance proinflammatory response. [In both pathways, furin / heparan sulphate could cleave S2’ site for successful viral entry and replication]. (Adapted and modified from https://www.genetex.com/Research/Overview/infectious_diseases/SARS-CoV-2?fbclid=IwAR0T8T8J75gdjt1z6Uuvh6KEdsJNDO6Ja8xuhso5Q0SDlkdkwATY077cMxo)