Abstract
Severe acute respiratory syndrome virus 2 (SARS-CoV-2) is responsible for the current global coronavirus disease 2019 (COVID-19) pandemic, infecting millions of people and causing hundreds of thousands of deaths. The viral entry of SARS-CoV-2 depends on an interaction between the receptor-binding domain of its trimeric spike glycoprotein and the human angiotensin-converting enzyme 2 (ACE2) receptor. A better understanding of the spike/ACE2 interaction is still required to design anti-SARS-CoV-2 therapeutics. Here, we investigated the degree of cooperativity of ACE2 within both the SARS-CoV-2 and the closely related SARS-CoV-1 membrane-bound S glycoproteins. We show that there exist differential inter-protomer conformational transitions between both spike trimers. Interestingly, the SARS-CoV-2 spike exhibits a positive cooperativity for monomeric soluble ACE2 binding when compared to the SARS-CoV-1 spike, which might have more structural restraints. Our findings can be of importance in the development of therapeutics that block the spike/ACE2 interaction.
Highlights
Severe acute respiratory syndrome virus 2 (SARS-CoV-2) is the cause of the current and rapidly evolving coronavirus disease 2019 (COVID-19) pandemic
Recent studies have compared the spike glycoproteins of SARS-CoV-1 and SARS-CoV-2, with a 76% amino acid sequence identity between the two and a 74% amino acid sequence identity between their receptor-binding domain (RBD) [13] which directly contribute to the engagement of angiotensin-converting enzyme 2 (ACE2)
Luciferase-expressing recombinant viruses in a final volume of 100 μL were incubated with increasing concentrations of soluble ACE2 (0 to 11,500 nM), ACE2-Fc (0 to 500 nM), or the monoclonal antibody CR3022 (0 to 270 nM) for 1 h at 37 ◦ C and were added to the target cells for an additional 4 hours followed by incubation for 48 h at 37 ◦ C; the medium was removed from each well, and the cells were lysed by the addition of 30 μL of passive lysis buffer (Promega, Madison, WI, USA) followed by three freeze–thaw cycles
Summary
Severe acute respiratory syndrome virus 2 (SARS-CoV-2) is the cause of the current and rapidly evolving coronavirus disease 2019 (COVID-19) pandemic. One potential therapeutic target receiving significant attention is the interaction between the SARS-CoV-2 spike (S) glycoprotein and its receptor, human angiotensin-converting enzyme 2 (ACE2). The S glycoprotein can only bind to ACE2 with the RBD in the “up” state and this results in the dissociation of the trimer [5,6]. Viruses 2020, 12, 1104 both the SARS-CoV-1 and SARS-CoV-2 viruses [7,8], is a type I membrane protein [9] and the soluble version of ACE2 has been shown to bind both S glycoproteins and block viral entry [10]. Recent studies have compared the spike glycoproteins of SARS-CoV-1 and SARS-CoV-2, with a 76% amino acid sequence identity between the two and a 74% amino acid sequence identity between their RBDs [13] which directly contribute to the engagement of ACE2. Our results further highlight conformational differences between the SARS-CoV-1 and SARS-CoV-2 spike glycoproteins
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