Cryo-EM structures of PP2A:B55-FAM122A and PP2A:B55-ARPP19

Area of Science:

• Molecular biology
• Structural biology
• Biochemistry

Background:

• Cell cycle progression is regulated by dynamic phosphorylation events.
• Mitotic exit is primarily controlled by phosphatases, particularly PP2A:B55.
• Inhibition of PP2A:B55 by ARPP19 and FAM122A is critical for successful mitosis, but the mechanism remains unclear.

Purpose of the Study:

• To elucidate the molecular mechanisms by which ARPP19 and FAM122A inhibit PP2A:B55.
• To determine the structural basis of PP2A:B55 inhibition by these intrinsically disordered proteins.

Main Methods:

• Single-particle cryo-electron microscopy (cryo-EM) to determine structures of PP2A:B55 bound to inhibitors.
• Nuclear Magnetic Resonance (NMR) spectroscopy to study protein interactions.
• Biophysical and biochemical assays to characterize binding and inhibition.

Main Results:

• The study determined the cryo-EM structures of PP2A:B55 in complex with phosphorylated ARPP19 and FAM122A.
• Both ARPP19 and FAM122A bind to PP2A:B55 through distinct mechanisms, utilizing multiple binding sites on the B55 subunit.
• NMR studies corroborated the distinct binding modes observed in the structural analysis.

Conclusions:

• ARPP19 and FAM122A inhibit PP2A:B55 through unique molecular interactions.
• The findings provide a structural and mechanistic understanding of PP2A:B55 regulation by intrinsically disordered proteins.
• This research offers a molecular roadmap for developing therapeutics targeting PP2A:B55-related diseases.