Flexibility in the PP1:spinophilin holoenzyme.

Protein phosphatase 1 (PP1) interacts with ∼200 regulatory proteins to form holoenzymes, which target PP1 to specific locations and regulate its specificity. While it is known that many PP1 regulatory proteins are dynamic in the unbound state, much less is known about the residual flexibility after PP1 holoenzyme formation. Here, we have used small angle X-ray scattering to investigate the flexibility of the PP1:spinophilin holoenzyme in solution. Collectively, our data shows that the PP1:spinophilin holoenzyme is dynamic in solution, which allows for an increased capture radius of spinophilin and is likely important for its biological role.