Hydrogen bonding is interrupted, but the distance is only slightly larger than observed in apo EPAC1, and does not reach the 40-60 Å range observed with cAMP (Supplementary Figure ). While I942 forms hydrogen bond interactions with residues 279-281, similar to cAMP, the interaction with G269 is not always observed (Figure ). Therefore the distance between the two ends of the PBC remains higher than observed with cAMP (Figure ), corresponding to a more "out" PBC conformation. Figure compares the conformations of the PBC and the hinge with cAMP and I942, and illustrates how the gap required to accommodate the disordered hinge C-terminus between the hinge and the PBC is not present, preventing full activation of EPAC1. This is also reflected in the RMSF values of hinge residues 303-309 in EPAC1-I942, which show an increase in fluctuation but do not reach the same levels as cAMP (Figure ). Additionally, the napthyl group on I942 cannot form the same active state stabilizing interactions than cAMP with K353 and E315 from the lid region. Therefore I942 fails both to fully activate EPAC1, and to stabilize the active state once it is populated.