Mutations in spike protein and allele variations in ACE2 impact targeted therapy strategies against SARS-CoV-2.

Coronavirus disease 2019 (COVID-19), which is caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), has spread rapidly worldwide with high rates of transmission and substantial mortality. To date, however, no effective treatments or enough vaccines for COVID-19 are available. The roles of angiotensin converting enzyme 2 (ACE2) and spike protein in the treatment of COVID-19 are major areas of research. In this study, we explored the potential of ACE2 and spike protein as targets for the development of antiviral agents against SARS-CoV-2. We analyzed clinical data, genetic data, and receptor binding capability. Clinical data revealed that COVID-19 patients with comorbidities related to an abnormal renin-angiotensin system exhibited more early symptoms and poorer prognoses. However, the relationship between ACE2 expression and COVID-19 progression is still not clear. Furthermore, if ACE2 is not a good targetable protein, it would not be applicable across a wide range of populations. The spike-S1 receptor-binding domain that interacts with ACE2 showed various amino acid mutations based on sequence analysis. We identified two spike-S1 point mutations (V354F and V470A) by receptor-ligand docking and binding enzyme-linked immunosorbent assays. These variants enhanced the binding of the spike protein to ACE2 receptors and were potentially associated with increased infectivity. Importantly, the number of patients infected with the V354F and V470A mutants has increased with the development of the SARS-CoV-2 pandemic. These results suggest that ACE2 and spike-S1 are likely not ideal targets for the design of peptide drugs to treat COVID-19 in different populations.

Coordination of two sequential ester-transfer reactions: exogenous guanosine binding promotes the subsequent omegaG binding to a group I intron.

Self-splicing of group I introns is accomplished by two sequential ester-transfer reactions mediated by sequential binding of two different guanosine ligands, but it is yet unclear how the binding is coordinated at a single G-binding site. Using a three-piece trans-splicing system derived from the Candida intron, we studied the effect of the prior GTP binding on the later omegaG binding by assaying the ribozyme activity in the second reaction. We showed that adding GTP simultaneously with and prior to the esterified omegaG in a substrate strongly accelerated the second reaction, suggesting that the early binding of GTP facilitates the subsequent binding of omegaG. GTP-mediated facilitation requires C2 amino and C6 carbonyl groups on the Watson-Crick edge of the base but not the phosphate or sugar groups, suggesting that the base triple interactions between GTP and the binding site are important for the subsequent omegaG binding. Strikingly, GTP binding loosens a few local structures of the ribozyme including that adjacent to the base triple, providing structural basis for a rapid exchange of omegaG for bound GTP.