Structural and activity characterization of human PHPT1 after oxidative modification.

Area of Science:

• Biochemistry
• Molecular Biology
• Enzymology

Background:

• Phosphohistidine phosphatase 1 (PHPT1) is a key mammalian enzyme regulating phosphohistidine levels.
• Its roles span signaling, lipid metabolism, and ion transport.
• Post-translational modifications influencing PHPT1 activity remain largely uncharacterized.

Purpose of the Study:

• To investigate the structural and functional consequences of hydrogen peroxide (H2O2)-induced oxidation on human PHPT1 (hPHPT1).
• To identify specific sites of oxidation and assess their impact on enzyme activity.

Main Methods:

• Liquid chromatography-tandem mass spectrometry (LC-MS/MS) for site-specific oxidation quantification.
• Explicit solvent molecular dynamics simulations to model structural changes.
• A novel mass spectrometry-based assay to evaluate enzyme function.

Main Results:

• H2O2 exposure selectively oxidizes hPHPT1 at Met95, located in the substrate-binding region.
• Molecular dynamics simulations suggest minimal structural impact on the apo-state catalytic site.
• Oxidation at Met95 does not negatively affect hPHPT1 enzymatic activity.
• Findings challenge the common view of protein oxidation as solely a loss-of-function modification.

Conclusions:

• Met95 oxidation may alter hPHPT1 activity by affecting intermediate state stability rather than direct catalytic site structure.
• Protein oxidation can have non-detrimental or even regulatory roles.
• This study provides new insights into the post-translational regulation of PHPT1.