4X9V:
reference: Neighbor-directed Histidine N(tau)-Alkylation: A Route to Imidazolium-containing Phosphopeptide Macrocycles., Qian WJ, Park JE, Grant R, Lai CC, Kelley JA, Yaffe MB, Lee KS, Burke TR, Biopolymers. 2015 Jul 7. doi: 10.1002/bip.22698. PMID: 26152807

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