2WQS:
reference: Two Intramolecular Isopeptide Bonds are Identified in the Crystal Structure of the Streptococcus gordonii SspB C-terminal Domain., Forsgren N, Lamont RJ, Persson K, J Mol Biol. 2010 Feb 4. PMID: 20138058

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