ITC measurements with PKA were carried out in a buffer containing 30 mM HEPES, 100 mM NaCl, 10 mM MgCl 2 , pH 7.4, 2% (v/v) DMSO) at 25°C. The titration protocol consisted of 19 injections, the first of which was 0.4 µL, followed by 18 titrations of 2 µL each.