The current COVID-19 pandemic has already had a devastating impact across the world. SARS-CoV-2 (the virus causing COVID-19) is known to use its surface spike (S) protein's receptor binding domain (RBD) to interact with the angiotensin-converting enzyme 2 (ACE2) receptor expressed on many human cell types. The RBD–ACE2 interaction is a crucial step to mediate the host cell entry of SARS-CoV-2. Recent studies indicate that the ACE2 interaction with the SARS-CoV-2 S protein has higher affinity than its binding with the structurally identical S protein of SARS-CoV-1, the virus causing the 2002-2004 SARS epidemic. However, the biophysical mechanism behind such binding affinity difference is unclear. This study utilizes a combined single-molecule force spectroscopy and steered molecular dynamics (SMD) simulation approach to quantify the specific interactions between CoV-2 or CoV-1 RBD and ACE2. Depending on the loading rates, the unbinding forces between CoV-2 RBD and ACE2 range from 70 to 110 pN, and are 30-50% higher than those of CoV-1 RBD and ACE2 under similar loading rates. SMD results indicate that CoV-2 RBD interacts with the N-linked glycan on Asn90 of ACE2. This interaction is mostly absent in the CoV-1 RBD–ACE2 complex. During the SMD simulations, the extra RBD-N-glycan interaction contributes to a greater force and prolonged interaction lifetime. The observation is confirmed by our experimental force spectroscopy study. After the removal of N-linked glycans on ACE2, its mechanical binding strength with CoV-2 RBD decreases to a similar level of the CoV-1 RBD–ACE2 interaction. Together, the study uncovers the mechanism behind the difference in ACE2 binding between SARS-CoV-2 and SARS-CoV-1, and could aid in the development of new strategies to block SARS-CoV-2 entry.

中文翻译：

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SARS-CoV-2穗状RBD和人ACE2蛋白-蛋白质相互作用的生物力学表征。

当前的COVID-19大流行已经在全球范围内产生了破坏性影响。众所周知，SARS-CoV-2（引起COVID-19的病毒）利用其表面刺突（S）蛋白的受体结合域（RBD）与许多人类细胞类型上表达的血管紧张素转化酶2（ACE2）受体相互作用。RBD-ACE2相互作用是介导SARS-CoV-2宿主细胞进入的关键步骤。最近的研究表明，ACE2与SARS-CoV-2 S蛋白的相互作用比与结构相同的SARS-CoV-1 S蛋白的结合具有更高的亲和力，该病毒导致2002-2004 SARS流行。但是，这种结合亲和力差异背后的生物物理机制尚不清楚。这项研究利用组合的单分子力谱和转向分子动力学（SMD）模拟方法来量化CoV-2或CoV-1 RBD与ACE2之间的特定相互作用。根据加载速率，在相似的加载速率下，CoV-2 RBD和ACE2之间的解粘力范围为70至110 pN，比CoV-1 RBD和ACE2高30-50％。SMD结果表明CoV-2 RBD与ACE2的Asn90上的N-连接聚糖相互作用。在CoV-1 RBD-ACE2复合物中，这种相互作用大部分是不存在的。在SMD模拟过程中，额外的RBD-N-聚糖相互作用会产生更大的作用力，并延长相互作用寿命。我们的实验力光谱学研究证实了这一发现。去除ACE2上的N-连接聚糖后，它与CoV-2 RBD的机械结合强度降低到与CoV-1 RBD-ACE2相互作用相似的水平。总之，该研究揭示了SARS-CoV-2和SARS-CoV-1之间ACE2结合差异的背后机制，并可能有助于开发阻止SARS-CoV-2进入的新策略。