1VQD:
reference: Potential use of additivity of mutational effects in simplifying protein engineering., Skinner MM, Terwilliger TC, Proc Natl Acad Sci U S A 1996 Oct 1;93(20):10753-7. PMID: 8855252

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