1Z5F:
reference: Roles of N-terminal pyroglutamate in maintaining structural integrity and pKa values of catalytic histidine residues in bullfrog ribonuclease 3., Lou YC, Huang YC, Pan YR, Chen C, Liao YD, J Mol Biol. 2006 Jan 20;355(3):409-21. Epub 2005 Nov 10. PMID: 16309702

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