6B00:
reference: Structural insights into a thermostable variant of human carbonic anhydrase II., Kean KM, Porter JJ, Mehl RA, Karplus PA, Protein Sci. 2017 Nov 15. doi: 10.1002/pro.3347. PMID: 29139171

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