Abstract：
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.
摘要：
唾液有助于先天免疫系统，这表明它可以防止SARS-CoV-2进入。我们使用生物层干涉法和下拉测定法研究了健康唾液蛋白与血管紧张素转换酶2（ACE2）结合的能力。使用酶联免疫吸附测定法确定了它们对SARS-CoV-2刺突蛋白S1（S1）和ACE2的受体结合域之间结合的影响。唾液与ACE2结合并破坏了S1与ACE2的结合，并鉴定了四种ACE2结合的唾液蛋白，包括阳离子组蛋白H2A和中性粒细胞弹性蛋白酶，抑制S1-ACE2相互作用。小牛胸腺组蛋白（ct-组蛋白）也与组蛋白H2A一样有效地抑制结合。基于细胞的感染测定的结果表明ct-组蛋白抑制SARS-CoV-2假病毒侵入表达ACE2的宿主细胞。制造的多肽，如ε-聚-L-赖氨酸，还破坏了S1-ACE2结合，表明唾液蛋白的阳离子特性在ACE2结合中的重要性。总的来说,我们证明，带正电荷的唾液蛋白通过掩盖ACE2的带负电荷的表面而成为SARS-CoV-2进入的屏障，并认为阳离子多肽代表了针对COVID-19的预防性和治疗性治疗。
