%0 Journal Article
%T Cloaking the ACE2 receptor with salivary cationic proteins inhibits SARS-CoV-2 entry.
%A Yoshizato K
%A Taira T
%A Sato-Matsubara M
%A Sekiguchi S
%A Yabunaka Y
%A Kira Y
%A Ohashi T
%A Daikoku A
%A Ofusa K
%A Kadono C
%A Oikawa D
%A Matsubara T
%A Nakagama Y
%A Kido Y
%A Tokunaga F
%A Ikeda K
%A Kaneko A
%A Kawada N
%J J Biochem
%V 172
%N 4
%D Sep 2022 30
%M 35792074
%F 3.241
%R 10.1093/jb/mvac054
%X Saliva contributes to the innate immune system, which suggests that it can prevent SARS-CoV-2 entry. We studied the ability of healthy salivary proteins to bind to angiotensin-converting enzyme 2 (ACE2) using biolayer interferometry and pull-down assays. Their effects on binding between the receptor-binding domain of the SARS-CoV-2 spike protein S1 (S1) and ACE2 were determined using an enzyme-linked immunosorbent assay. Saliva bound to ACE2 and disrupted the binding of S1 to ACE2 and four ACE2-binding salivary proteins were identified, including cationic histone H2A and neutrophil elastase, which inhibited the S1-ACE2 interaction. Calf thymus histone (ct-histone) also inhibited binding as effectively as histone H2A. The results of a cell-based infection assay indicated that ct-histone suppressed SARS-CoV-2 pseudoviral invasion into ACE2-expressing host cells. Manufactured polypeptides, such as ε-poly-L-lysine, also disrupted S1-ACE2 binding, indicating the importance of the cationic properties of salivary proteins in ACE2 binding. Overall, we demonstrated that positively charged salivary proteins are a barrier against SARS-CoV-2 entry by cloaking the negatively charged surface of ACE2 and provided a view that the cationic polypeptides represent a preventative and therapeutic treatment against COVID-19.