Uncovering cryptic pockets in the SARS-CoV-2 spike glycoprotein
The recent global COVID-19 pandemic has prompted a rapid response in terms of vaccine and drug development targeting the viral pathogen, severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). In this work, we modelled a complete membrane-embedded SARS-CoV-2 spike (S) protein, the primary target of vaccine and therapeutics development, based on available structural data and known glycan content. We then used molecular dynamics (MD) simulations to study the system in the presence of benzene probes designed to enhance discovery of cryptic, potentially druggable pockets on the S protein surface. We uncovered a novel cryptic pocket with promising druggable properties located underneath the 617-628 loop, which was shown to be involved in the formation of S protein multimers on the viral surface. A marked multi-conformational behaviour of this loop in simulations was validated using hydrogen-deuterium exchange mass spectrometry (HDX-MS) experiments, supportive of opening and closing dynamics. Interestingly, the pocket is also the site of the D614G mutation, known to be important for SARS-CoV-2 fitness, and within close proximity to mutations in the novel SARS-CoV-2 strains B.1.1.7 and B.1.1.28, both of which are associated with increased transmissibility and severity of infection. The pocket was present in systems emulating both immature and mature glycosylation states, suggesting its druggability may not be dependent upon the stage of virus maturation. Overall, the predominantly hydrophobic nature of the cryptic pocket, its well conserved surface, and proximity to regions of functional relevance in viral assembly and fitness are all promising indicators of its potential for therapeutic targeting. Our method also successfully recapitulated hydrophobic pockets in the receptor binding domain and N-terminal domain associated with detergent or lipid binding in prior cryo-electron microscopy (cryo-EM) studies. Collectively, this work highlights the utility of the benzene mapping approach in uncovering potential druggable sites on the surface of SARS-CoV-2 targets.