Cleavage of S protein into S1:S2

Spike protein S1: attaches the virion to the cell membrane by interacting with host receptor, initiating the infection.<br>
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Spike protein S2: Acts as a viral fusion peptide which is unmasked following S2 cleavage occurring upon virus endocytosis. <br>
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Spike protein S2: mediates fusion of the virion and cellular membranes by acting as a class I viral fusion protein. Under the current model, the protein has at least three conformational states: pre-fusion native state, pre-hairpin intermediate state, and post-fusion hairpin state. During viral and target cell membrane fusion, the coiled coil regions (heptad repeats) assume a trimer-of-hairpins structure, positioning the fusion peptide in close proximity to the C-terminal region of the ectodomain. The formation of this structure appears to drive apposition and subsequent fusion of viral and target cell membranes. <br>
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Within the host cell endocytic vesicle, SARS-CoV-1 Spike (S) protein is cleaved between residues 797 and 798 by cathepsin L1 (CTSL) (Huang et al. 2006). The roles of S protein in viral binding to the host cell membrane and fusion of viral and host cell membranes and thus the central role of S protein in determining the host range and tissue tropisms of the virus are reviewed by Belouzard et al. (2012).

刺突蛋白S1：通过与其宿主受体的相互作用，将病毒颗粒附着于细胞膜上，从而启动感染过程。<br><br>刺突蛋白S2：充当病毒融合肽，在病毒内吞作用后发生的S2切割过程中被暴露。它作为一类病毒融合蛋白，介导病毒颗粒与细胞膜的融合。根据当前模型，该蛋白至少存在三种构象状态：融合前天然状态、融合前发夹中间状态和融合后发夹状态。在病毒与靶细胞膜融合过程中，卷曲螺旋区域（七股重复序列）形成发夹三聚体结构，将融合肽定位在包膜外域C端区域附近。这种结构的形成似乎推动了病毒颗粒与靶细胞膜的靠近和随后的融合。在宿主细胞内吞泡中，SARS-CoV-1刺突（S）蛋白在残基797和798之间被猫蛋白酶L1（CTSL）切割（Huang等人，2006年）。S蛋白在病毒与宿主细胞膜结合以及病毒与宿主细胞膜融合中的作用，以及S蛋白在决定病毒宿主范围和组织嗜性中的核心作用，由Belouzard等人（2012年）进行了综述。