How phosphorylation activates the protein phosphatase-1 • inhibitor-2 complex

Area of Science:

• Biochemistry
• Structural Biology
• Enzymology

Background:

• Protein phosphorylation is a key regulatory mechanism, but atomic details are often lacking.
• Inhibitor-2 (I2) inhibits protein phosphatase-1 (PP1) by blocking its active site.
• Phosphorylation of I2 at Thr74 activates PP1 without causing dissociation.

Purpose of the Study:

• To elucidate the atomic-level structural changes induced by I2 Thr74 phosphorylation that lead to PP1 activation.
• To understand the role of disordered regions in allosteric regulation of enzyme activity.

Main Methods:

• Integration of NMR restraints with crystallographic data to model disordered protein segments.
• Molecular dynamics simulations to study the impact of phosphorylation on protein-protein interactions and dynamics.
• Analysis of residue dynamics and allosteric pathways.

Main Results:

• I2 Thr74 phosphorylation significantly increased the displacement of Tyr149 from the PP1 active site and repositioned the inhibitory helix.
• Phosphorylation led to altered metal binding and reduced affinity of I2 to the PP1 active site.
• Simulations revealed allosteric pathways where phosphorylated Thr74 motions propagate to the PP1 active site, facilitating activation.

Conclusions:

• Phosphorylation of I2 Thr74 triggers dynamic structural rearrangements, enabling PP1 active site access and activation.
• Unstructured regions in regulatory proteins can mediate allosteric control through enhanced dynamics.
• This study provides atomic-level insights into the mechanism of PP1-I2 complex regulation.