Inhibitory mechanism of Ambroxol and Bromhexine Hydrochlorides as potent blockers of molecular interaction between SARS-CoV-2 spike protein and human angiotensin-converting Enzyme-2

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infects the host cells through interaction of its spike protein with human angiotensin-converting enzyme 2 (hACE-2). High binding affinity between the viral spike protein and host cells hACE-2 receptor has been reported to enhance the viral infection. Thus, the disruption of this molecular interaction will lead to reduction in viral infectivity. This study, therefore, aimed to analyze the inhibitory potentials of two mucolytic drugs; Ambroxol hydrochlorides (AMB) and Bromhexine hydrochlorides (BHH), to serve as potent blockers of these molecular interactions and alters the binding affinity/efficiency between the proteins employing computational techniques. The study examined the effects of binding of each drug at the receptor binding domain (RBD) of the spike protein and the exopeptidase site of hACE-2 on the binding affinity (ΔG_bind) and molecular interactions between the two proteins. Binding affinity revealed that the binding of the two drugs at the RBD-ACE-2 site does not alter the binding affinity and molecular interaction between the proteins. However, the binding of AMB (−56.931 kcal/mol) and BHH (−46.354 kcal/mol) at the exopeptidase site of hACE-2, significantly reduced the binding affinities between the proteins compared to the unbound, ACE-2-RBD complex (−64.856 kcal/mol). The result further showed the two compounds have good affinity at the hACE-2 site, inferring they might be potent inhibitors of hACE-2. Residue interaction networks analysis further revealed the binding of the two drugs at the exopeptidase site of hACE-2 reduced the number of interacting amino residues, subsequently leading to loss of interactions between the two proteins, with BHH showing better reduction in the molecular interaction and binding affinity than AMB. The result of the structural analyses additionally, revealed that the binding of the drugs considerably influences the dynamic of the complexes when compared to the unbound complex. The findings from this study suggest the binding of the two drugs at the exopeptidase site reduces the binding effectiveness of the proteins than their binding at the RBD site, and consequently might inhibit viral attachment and entry.