1XAS:
reference: Crystal structure, at 2.6-A resolution, of the Streptomyces lividans xylanase A, a member of the F family of beta-1,4-D-glycanases., Derewenda U, Swenson L, Green R, Wei Y, Morosoli R, Shareck F, Kluepfel D, Derewenda ZS, J Biol Chem 1994 Aug 19;269(33):20811-4. PMID: 8063693

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