1RL3:
reference: RIalpha subunit of PKA: a cAMP-free structure reveals a hydrophobic capping mechanism for docking cAMP into site B., Wu J, Brown S, Xuong NH, Taylor SS, Structure. 2004 Jun;12(6):1057-65. PMID: 15274925

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