The tandem Src homology 2 domain of the Syk kinase: a molecular device that adapts to interphosphotyrosine distances.

Conformational flexibility is important for protein function. However, information on the range of conformations accessible to macromolecules in the unbound state is often difficult to obtain. By using the model system of the tandem Src homology 2 domain (i.e., two adjacent Src homology 2 domains) of the Syk kinase, we report a method combining calorimetric and crystallographic measurements that reveals the preexistence of a conformational equilibrium in the unbound state, and that shows that this equilibrium is crucial for function.