3CDI:
reference: Crystal structure of Escherichia coli PNPase: central channel residues are involved in processive RNA degradation., Shi Z, Yang WZ, Lin-Chao S, Chak KF, Yuan HS, RNA. 2008 Nov;14(11):2361-71. Epub 2008 Sep 23. PMID: 18812438

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