3IGN:
reference: Crystal structure of a catalytically active GG(D/E)EF diguanylate cyclase domain from Marinobacter aquaeolei with bound c-di-GMP product., Vorobiev SM, Neely H, Yu B, Seetharaman J, Xiao R, Acton TB, Montelione GT, Hunt JF, J Struct Funct Genomics. 2012 Sep;13(3):177-83. doi: 10.1007/s10969-012-9136-4., Epub 2012 Jul 29. PMID: 22843345

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