Severe acute respiratory syndrome coronavirus (SARS-CoV)-2 is an enveloped virus responsible for the COVID-19 pandemic. The emergence of new potentially more transmissible and vaccine-resistant variants of SARS-CoV-2 is an ever-present threat. Thus, it remains essential to better understand innate immune mechanisms that can inhibit the virus. One component of the innate immune system with broad antipathogen, including antiviral, activity is a group of cationic immune peptides termed defensins. The ability of defensins to neutralize enveloped and non-enveloped viruses and to inactivate numerous bacterial toxins correlate with their ability to promote the unfolding of proteins with high conformational plasticity. We found that human neutrophil α-defensin HNP1 binds to SARS-CoV-2 Spike protein with submicromolar affinity that is more than 20 fold stronger than its binding to serum albumin. As such, HNP1, as well as a θ-defensin retrocyclin RC-101, both interfere with Spike-mediated membrane fusion, Spike-pseudotyped lentivirus infection, and authentic SARS-CoV-2 infection in cell culture. These effects correlate with the abilities of the defensins to destabilize and precipitate Spike protein and inhibit the interaction of Spike with the ACE2 receptor. Serum reduces the anti-SARS-CoV-2 activity of HNP1, though at high concentrations, HNP1 was able to inactivate the virus even in the presence of serum. Overall, our results suggest that defensins can negatively affect the native conformation of SARS-CoV-2 Spike, and that α- and θ-defensins may be valuable tools in developing SARS-CoV-2 infection prevention strategies.

严重急性呼吸系统综合症冠状病毒 (SARS-CoV)-2 是一种导致 COVID-19 大流行的包膜病毒。SARS-CoV-2 的新变种的出现可能更具传播性和疫苗抗性，是一个永远存在的威胁。因此，更好地了解可以抑制病毒的先天免疫机制仍然很重要。具有广泛抗病原体（包括抗病毒）活性的先天免疫系统的一个组成部分是一组称为防御素的阳离子免疫肽。防御素中和包膜和非包膜病毒以及灭活多种细菌毒素的能力与其促进具有高构象可塑性的蛋白质展开的能力相关。我们发现人中性粒细胞 α-防御素 HNP1 与 SARS-CoV-2 刺突蛋白的结合具有亚微摩尔亲和力，比其与血清白蛋白的结合强 20 多倍。因此，HNP1 以及 θ-防御素逆转录环素 RC-101 都会干扰刺突介导的膜融合、刺突假型慢病毒感染和细胞培养中真正的 SARS-CoV-2 感染。这些作用与防御素破坏和沉淀刺突蛋白以及抑制刺突蛋白与 ACE2 受体相互作用的能力相关。血清降低了 HNP1 的抗 SARS-CoV-2 活性，尽管在高浓度下，HNP1 即使在血清存在的情况下也能够使病毒失活。总体而言，我们的结果表明防御素会对 SARS-CoV-2 刺突的天然构象产生负面影响，