Fig. 6: Structural explanations for substitutions.

Ibrutinib, top, and RN-484, bottom, are used as examples for covalent and non-covalent inhibitors, respectively. Substitutions of C481 prevent covalent binding of inhibitors, and the side chains can affect the positioning of the inhibitor. Methionine and isoleucine replacements at gatekeeper 474 collide with the covalent inhibitors and affect binding affinity. Non-covalent inhibitors have different binding mode and side chains at 481 are further away from the inhibitor. The gatekeeper residue is important for binding of these inhibitors, as well.