meCocan - Towards a mechanistic understanding of the interaction of SARS-CoV-2 spike glycoprotein and host heparan sulphate proteoglycans

• Applicant: Professorin Dr. Rebecca Wade
• Subject Area: Biophysics ; Bioinformatics and Theoretical Biology ; Virology
• Term: from 2021 to 2022
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 458623378

The SARS-CoV-2 spike glycoprotein (SGP) plays a key role in host infection by the virus, which ultimately leads to the COVID-19 disease. The SGP on the virion surface attaches to host cells by the binding its receptor-binding domain (RBD) to human angiotensin converting enzyme 2 (ACE2). There is increasing evidence that viral infection is facilitated by host cell heparan sulphate proteoglycans (HSPGs) that act as co-receptors and may influence host susceptibility. However, the mechanism by which HSPGs affect virus-host cell binding and entry is largely unknown. The HSPGs possess strongly anionic glycosaminoglycan (GAG) chains. Although three basic GAG binding motifs (GAG-BM) have been identified on the SGP, prior studies have focused on the GAG-BM in the RBD. They have characterized the binding of heparin, a simplified model for HSPGs, to this site, and have shown that the SGP, ACE2 and heparin can form a ternary complex. However, the differences in this GAG-BM and its surroundings between SARS-CoV1 and SARS-CoV2 are quite modest. Therefore, we propose that other factors are needed to explain the high infectivity of SARS-CoV2. Notably, in addition to the two conserved GAG-BMs in previous viral strains, a novel basic insertion has been identified in the S1/S2 region of SARS-CoV2 SGP. This basic insertion has a cleavage site motif that is targeted by the host furin protease to cleave the SGP prior to virus-host cell fusion. We hypothesize that the basic S1/S2 site may play a critical role in interacting with HSPGs and facilitating SARS-CoV2 host cell infection. In the meCocan project, we propose a multidisciplinary approach, employing computational and experimental methods, to investigate (i) the role of the S1/S2 basic motif in SARS CoV2 SPG-HSPG binding; (ii) the mechanistic and allosteric effects of HSPGs on SGP conformation and SGP-ACE2 interactions, and therefore virus-host cell infection, and (iii) the relation between the S1/S2 basic motif, SPG-HSPG interaction and host susceptibility. The specific aims are to perform:1) molecular dynamics simulations to derive validated models of the open and closed glycosylated SGP ectodomain with long (>30mer) heparin chains and in the ternary complex with heparins and ACE2;2) surface plasmon resonance analysis to measure the binding of glycosylated wild-type and mutant SGP (S1/S2 basic site neutralized) to heparin and/or ACE2 to determine the role of the S1/S2 site in the binding of HSPGs;3) binding assays on living cells to evaluate the ability of wild-type and mutant SGP to bind cells that differently express HSPGs to investigate their role in host susceptibility.The results of the meCocan project are expected to impact molecular and translational medicine in the COVID-19 field by providing new insights into the mechanisms of coronavirus infection, new therapeutic targets for the development of SARS-CoV2 antiviral compounds, and a foundation for the design of inhibitors of host-cell infection.

• DFG Programme: Research Grants
• International Connection: Italy
• Cooperation Partner: Professor Dr. Marco Rusnati