PPM1B utilizes a trinuclear metal architecture for phosphatase activity

Area of Science:

• Biochemistry
• Molecular Biology
• Immunology

Background:

• The metal-dependent protein phosphatase (PPM/PP2C) family regulates innate immunity and cell death.
• A conserved third metal ion (M3) is crucial for PPM/PP2C activity, but its precise chemical role is unknown.
• PPM1B is implicated in cell death during Pseudomonas aeruginosa infection.

Purpose of the Study:

• To elucidate the chemical mechanism of the third metal ion (M3) in PPM phosphatases.
• To understand the role of PPM1B in Pseudomonas aeruginosa infection and cell death.
• To explore the M3 site as a potential drug target.

Main Methods:

• Biochemical assays to study PPM1B activity and substrate coordination.
• Structural analysis of the trinuclear metal center.
• In vivo studies of PPM1B function during Pseudomonas aeruginosa infection.

Main Results:

• PPM1B utilizes a trinuclear metal center where M3 directly coordinates the substrate phosphate.
• M3 facilitates in-line S_N2 hydrolysis by orienting the substrate and positioning a water molecule for protonation.
• M3's function is analogous to the arginine clamp in PPP phosphatases, indicating convergent evolution.

Conclusions:

• A three-metal catalytic mechanism for PPM phosphatases is defined, with M3 playing a key role in phosphate hydrolysis.
• PPM1B promotes cell death during Pseudomonas aeruginosa infection.
• The M3 site represents a conserved and druggable target for immune and infectious diseases.