3TNP:
reference: Structure and allostery of the PKA RIIbeta tetrameric holoenzyme., Zhang P, Smith-Nguyen EV, Keshwani MM, Deal MS, Kornev AP, Taylor SS, Science. 2012 Feb 10;335(6069):712-6. PMID: 22323819

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