Binding conformation of 16R within the active pocket of the 3CLpro. (a) Pose of 16R within the active site of the SARS-CoV 3CLpro. Hydrogen bonds (yellow dashes) are formed with Gly143, His163 and Glu166. (b) 16R assumes a similar pose when bound to the OC43 3CLpro. A notable difference is the loss a hydrogen bond with Glu166. Hydrogen bonds with Gly143 and His163 are however maintained.