SARSコロナウイルス
The first path the SARS coronavirus can take to enter the host cell is by endocytosis and uptake of the virus in an endosome. The receptor-attached spike protein is then activated by the host's pH-dependent cysteine protease cathepsin L. Activation of the receptor-attached spike protein causes a conformational change, and the subsequent fusion of the viral envelope with the endosomal wall.