2GKT:
reference: Structural insights into the non-additivity effects in the sequence-to-reactivity algorithm for serine peptidases and their inhibitors., Lee TW, Qasim MA, Laskowski M Jr, James MN, J Mol Biol. 2007 Mar 23;367(2):527-46. Epub 2007 Jan 9. PMID: 17266986

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