4YPJ:
reference: Crystal structure of beta-galactosidase from Bacillus circulans ATCC 31382 (BgaD) and the construction of the thermophilic mutants., Ishikawa K, Kataoka M, Yanamoto T, Nakabayashi M, Watanabe M, Ishihara S, Yamaguchi S, FEBS J. 2015 Apr 16. doi: 10.1111/febs.13298. PMID: 25879162

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