1FGB:
reference: The 2.4 A crystal structure of cholera toxin B subunit pentamer: choleragenoid., Zhang RG, Westbrook ML, Westbrook EM, Scott DL, Otwinowski Z, Maulik PR, Reed RA, Shipley GG, J Mol Biol 1995 Aug 25;251(4):550-62. PMID: 7658472

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