5Y4L:
reference: Identification of two antiviral inhibitors targeting 3C-like serine/3C-like protease of porcine reproductive and respiratory syndrome virus and porcine epidemic diarrhea virus., Shi Y, Lei Y, Ye G, Sun L, Fang L, Xiao S, Fu ZF, Yin P, Song Y, Peng G, Vet Microbiol. 2018 Jan;213:114-122. doi: 10.1016/j.vetmic.2017.11.031. Epub 2017, Nov 24. PMID: 29291994

This OCA Structure page
uses Jmol, developed by the Jmol Development Team (documentation).