3GUA:
reference: An ion selectivity filter in the extracellular domain of Cys-loop receptors reveals determinants for ion conductance., Hansen SB, Wang HL, Taylor P, Sine SM, J Biol Chem. 2008 Dec 26;283(52):36066-70. Epub 2008 Oct 21. PMID: 18940802

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