2KDL:
reference: A minimal sequence code for switching protein structure and function., Alexander PA, He Y, Chen Y, Orban J, Bryan PN, Proc Natl Acad Sci U S A. 2009 Dec 15;106(50):21149-54. Epub 2009 Nov 18. PMID: 19923431

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