5HPP:
reference: Square channels formed by a peptide derived from transthyretin., Yoo S, Kreutzer AG, Truex NL, Nowick JS, Chem Sci. 2016 Dec 1;7(12):6946-6951. doi: 10.1039/c6sc01927g. Epub 2016 Aug 1. PMID: 28451128

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