Dynamically Coupled Residues within the SH2 Domain of FYN Are Key to Unlocking Its Activity

Src kinase activity is controlled by various mechanisms involving a coordinated movement of kinase and regulatory domains. Notwithstanding the extensive knowledge related to the backbone dynamics, little is known about the more subtle side-chain dynamics within the regulatory domains and their role in the activation process. Here, we show through experimental methyl dynamic results and predicted changes in side-chain conformational couplings that the SH2 structure of Fyn contains a dynamic network capable of propagating binding information. We reveal that binding the phosphorylated tail of Fyn perturbs a residue cluster near the linker connecting the SH2 and SH3 domains of Fyn, which is known to be relevant in the regulation of the activity of Fyn. Biochemical perturbation experiments validate that those residues are essential for inhibition of Fyn, leading to a gain of function upon mutation. These findings reveal how side-chain dynamics may facilitate the allosteric regulation of the different members of the Src kinase family. [Display omitted] •Binding to the pY-tail of Fyn rigidifies the SH3-SH2 linker, inhibiting activity•We identify a side-chain dynamics network that explains the process•A residue cluster near the linker appears to act via a locking mechanism•Kinase assays validate the cluster's importance Huculeci et al. combine NMR side-chain relaxation experiments with predictions to reveal how binding to the phosphorylated tail of the Src family kinase Fyn transduces a signal through its SH2 domain, which regulates its activity. The results support a lock hypothesis that explains the rigidification of the SH2-SH3 linker.