Cloaking the ACE2 receptor with salivary cationic proteins inhibits SARS-CoV-2 entry

J Biochem. 2022 Sep 30;172(4):205-216. doi: 10.1093/jb/mvac054.


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.

Keywords: SARS-CoV-2 spike protein; angiotensin-converting enzyme 2; histone H2A; neutrophil elastase; saliva.

MeSH terms

  • Angiotensin-Converting Enzyme 2*
  • COVID-19*
  • Histones / metabolism
  • Humans
  • Leukocyte Elastase / metabolism
  • Peptidyl-Dipeptidase A / metabolism
  • Polylysine / metabolism
  • Protein Binding
  • SARS-CoV-2
  • Salivary Proteins and Peptides / metabolism
  • Salivary Proteins and Peptides / pharmacology
  • Spike Glycoprotein, Coronavirus


  • Histones
  • Salivary Proteins and Peptides
  • Spike Glycoprotein, Coronavirus
  • spike protein, SARS-CoV-2
  • Polylysine
  • Peptidyl-Dipeptidase A
  • ACE2 protein, human
  • Angiotensin-Converting Enzyme 2
  • Leukocyte Elastase