Wenjing Zhang, McGill University

Wenjing Zhang-1,2, Harshita Katiyar-1,2, Qinghua Pan-2, Chen Liang-1,2. (1-McGill University, 2-Lady Davis Institute)

Building & Escaping

The SARS-CoV-2 Spike protein is heavily glycosylated to shield its epitopes from antibody recognition. To evade innate immune sensors such as mannose-binding lectin (MBL) and the macrophage mannose receptor, virus-associated Spike protein minimizes high-mannose glycans while favouring complex glycans. When Spike protein is synthesized in the ER, it acquires high-mannose N-glycans which can only be converted to complex N-glycans by glycosyltransferases in the Golgi. Since SARS-CoV-2 particles assemble at the ER-Golgi intermediate compartment (ERGIC), where N-glycans are still high-mannose, it remains unclear how the virus-associated Spike undergoes maturation from high-mannose to complex N-glycans during viral egress. In this study, we examined the nature of N-glycans on SARS-CoV-2 Spike in infected cells and virus particles by employing glycosidases Endo H (cleaving high-mannose N-glycans) and PNGase F (cleaving complex N-glycans). The results showed that intracellular Spike was sensitive to Endo H treatment, whereas virus-associated Spike was resistant. This finding supports a model where Spike accumulates at ERGIC to participate in virion assembly, and subsequently undergoes N-glycan maturation as the virus particles egress. Similar observations were also made using a virus-like particle (VLP) system containing the viral structural proteins, membrane (M), envelope (E), nucleocapsid (N), and Spike (S). Interestingly, replacing SARS-CoV-2 M protein with SARS-CoV-1 M, prevented VLP-associated Spike from acquiring complex glycans, suggesting an M protein-mediated mechanism that enables the maturation of N-glycans on Spike from high-mannose to complex type. Disrupting this viral mechanism may sensitize SARS-CoV-2 particles to restriction by mannose-targeting innate immune defenses.