## Structural Proteins of SARS-CoV-2 **Key Point:** SARS-CoV-2 has four major structural proteins: spike (S), envelope (E), membrane (M), and nucleocapsid (N). Understanding their distinct functions is critical for exam success. ### Correct Structural Protein Functions | Protein | Function | Key Feature | |---------|----------|-------------| | **Spike (S)** | ACE2 receptor binding; viral entry | Primary neutralizing antibody target; RBD domain critical | | **Envelope (E)** | Ion channel; viroporin activity | Involved in viral assembly and pathogenesis; forms pentameric channels | | **Nucleocapsid (N)** | RNA binding; virion packaging | Most abundant structural protein; immunogenic | | **Membrane (M)** | Virion assembly; structural support | Non-glycosylated; organizes viral assembly at ER-Golgi | **High-Yield:** The M protein is NOT a glycoprotein and does NOT mediate receptor binding. The S protein (specifically its receptor-binding domain, RBD) is solely responsible for ACE2 attachment. The M protein is a non-glycosylated transmembrane protein that organizes the viral assembly process. ### Why Option 3 is Incorrect **Warning:** A common misconception is that the M protein has a role in receptor binding. This is FALSE. The M protein: - Is non-glycosylated (unlike S and E proteins) - Functions in virion assembly and structural organization - Does NOT bind to ACE2 or any host receptor - Interacts with other viral proteins (S, E, N) to form the virion **Clinical Pearl:** The spike protein's RBD is so immunologically important that most COVID-19 vaccines (mRNA, protein subunit) target only the S protein, not the M protein. [cite:Harrison 21e Ch 197]
Sign up free to access AI-powered MCQ practice with detailed explanations and adaptive learning.