Fig. 2

JA2-4 binds to the adenine-binding pocket of hPARG by virtue of the flexibility of the Tyr clasp. a 1.7 Å crystal structure of human PARG bound to JA2-4 reveals specific and extensive inhibitor interactions with the adenine-binding pocket. The 6´-thiocarbonyl sulfur of JA2-4 was assigned by comparing the size and orientation of the electron density to that of the corresponding 6´-carbonyl oxygen of JA2120 (Fig. 3b). JA2-4 is shown with a Fo-Fc map (contoured at 2σ) that was calculated prior to the addition of JA2-4 to the model. JA2-4 bound PARG catalytic domain shown in the enlarged box. b A structural comparison of the binding interactions of JA2-4 and ADP-HPD is consistent with a competitive inhibition mechanism for JA2-4. The structure of hPARG bound to ADP-HPD (wheat) is overlaid onto that bound to JA2-4 (white). The methylxanthine core of JA2-4 makes extensive interactions and occupies the same binding site as the adenosine moiety of ADP-HPD and. c The Tyr clasp changes conformation to enable binding of JA2-4. JA2-4 binding shifts the position of the Tyr clasp in concert with the rotation of the Tyr795 side chain and rearrangement of Arg671. The structural flexibility of the Tyr clasp creates room for JA2-4 and facilitates interactions with Asn869 and I726 that contribute to potent inhibition of PARG activity (IC₅₀ of 0.9 μM).PDB code: 6O9X (PARG/JA2-4), 6O9Y (PARG/JA2-8), 6OA0 (PARG/JA2-9).