Viral Structure

"Since its emergence in late 2019, the COVID-19 pandemic has resulted in millions of infections and fatalities worldwide. SARS-CoV-2 has rapidly evolved, producing highly transmissible variants such as Alpha, Beta, Delta, Gamma, and Omicron. Among these, Omicron (B.1.1.529) and its sublineages, including BA.5, XBB, EG.5, JN.1, KP.3, KP.3.1.1, and XEC, have become the dominant strains in the United States from 2022 to 2024 1-3. Structurally, SARS-CoV-2 consists of four major proteins: spike (S), membrane (M), envelope (E), and nucleocapsid (N). The S protein is essential for viral entry into host cells, making it a key target for antiviral strategies. It is composed of two functional subunits: S1 and S2. The S1 subunit contains the N-terminal domain (NTD) and the receptor-binding domain (RBD), which facilitate viral attachment by binding to the host cell receptor, angiotensin-converting enzyme 2 (ACE2). The S2 subunit is responsible for membrane fusion, enabling viral entry into host cells 1. Given its essential role in viral infection, the S protein remains central to both vaccine development and therapeutic interventions."