Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) first infects the host nasal mucosa, where the viral spike protein binds to angiotensin-converting enzyme 2 (ACE2) on the mucosal cells. This study aimed at searching host cell surface molecules that could contribute to the infection in two views; abundance on host cells and affinity to the spike protein. Since the nasal mucosa is lined by respiratory and olfactory epithelia, and both express an immunoglobulin superfamily member cell adhesion molecule 1 (CADM1), whether CADM1 would participate in the spike protein binding was examined. Immunohistochemistry on the mouse nasal cavity detected CADM1 strongly in the olfactory epithelium at cell-cell contacts and on the apical surface but just faintly in the respiratory epithelium. In contrast, ACE2 was detected in the respiratory, not olfactory, epithelium. When mice were administered intranasally with SARS-CoV-2 S1 spike protein and an anti-CADM1 ectodomain antibody separately, both were detected exclusively on the olfactory, not respiratory, epithelium. Then, the antibody and S1 spike protein were administered intranasally to mice in this order with an interval of 1 hour. After 3 hours, S1 spike protein was detected as a protein aggregate floating in the nasal cavity. Next, S1 spike protein labeled with fluorescein was added to the monolayer cultures of epithelial cells exogenously expressing ACE2 or CADM1. Quantitative detection of fluorescein bound to the cells revealed that S1 spike protein bound to CADM1 with affinity half as high as to ACE2. Consistently, docking simulation analyses revealed that S1 spike protein could bind to CADM1 three quarters as strongly as to ACE2 and that the interface of ACE2 was similar in both binding modes. Collectively, intranasal S1 spike protein appeared to prefer to accumulate on the olfactory epithelium, and CADM1 was suggested to contribute to this preference of S1 spike protein based on the molecular abundance and affinity.

中文翻译：

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细胞粘附分子 1 对 SARS-CoV-2 刺突蛋白与小鼠鼻粘膜结合的潜在贡献。

严重急性呼吸综合征冠状病毒 2 (SARS-CoV-2) 首先感染宿主鼻粘膜，病毒刺突蛋白与粘膜细胞上的血管紧张素转换酶 2 (ACE2) 结合。本研究旨在从两个角度寻找可能有助于感染的宿主细胞表面分子；宿主细胞上的丰度以及对刺突蛋白的亲和力。由于鼻粘膜衬有呼吸道上皮和嗅觉上皮，并且两者都表达免疫球蛋白超家族成员细胞粘附分子1（CADM1），因此检查了CADM1是否会参与刺突蛋白结合。小鼠鼻腔的免疫组织化学在细胞-细胞接触处的嗅上皮和心尖表面上强烈检测到 CADM1，但在呼吸道上皮中检测到微弱的 CADM1。相比之下，ACE2 在呼吸道上皮细胞而非嗅觉上皮细胞中检测到。当小鼠分别鼻内注射 SARS-CoV-2 S1 刺突蛋白和抗 CADM1 胞外域抗体时，两者均仅在嗅觉上皮细胞（而非呼吸道上皮细胞）上检测到。然后，将抗体和S1刺突蛋白依次鼻内给予小鼠，间隔1小时。3小时后，检测到S1刺突蛋白为漂浮在鼻腔中的蛋白聚集体。接下来，将荧光素标记的 S1 刺突蛋白添加到外源表达 ACE2 或 CADM1 的上皮细胞的单层培养物中。与细胞结合的荧光素的定量检测表明，S1 刺突蛋白与 CADM1 的结合亲和力仅为 ACE2 的一半。对接模拟分析一致表明，S1 刺突蛋白与 CADM1 的结合强度是与 ACE2 结合强度的四分之三，并且 ACE2 的界面在两种结合模式下相似。总的来说，鼻内 S1 刺突蛋白似乎更喜欢在嗅觉上皮上积聚，并且基于分子丰度和亲和力，CADM1 被认为有助于 S1 刺突蛋白的这种偏好。