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Updated: Jul 26, 2026

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The PX domain as a novel phosphoinositide- binding module.

T Ago¹, R Takeya, H Hiroaki

¹Medical Institute of Bioregulation, Kyushu University, 3-1-1 Maidashi, Higashi-ku, Fukuoka, 812-8582, Japan.

Biochemical and Biophysical Research Communications

|September 21, 2001

Summary

The phagocyte oxidase (phox) homology (PX) domain directly binds to phosphoinositides, acting as a novel membrane-targeting module. This discovery reveals the PX domain

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Identification of Inositol Phosphate or Phosphoinositide Interacting Proteins by Affinity Chromatography Coupled to Western Blot or Mass Spectrometry

Identification of Inositol Phosphate or Phosphoinositide Interacting Proteins by Affinity Chromatography Coupled to Western Blot or Mass Spectrometry

Published on: July 26, 2019

Area of Science:

Cell Biology
Molecular Biology
Biochemistry

Background:

The phox (phagocyte oxidase) homology (PX) domain is found in proteins regulating cellular processes.
These proteins include mammalian p40(phox) and p47(phox), and yeast's Bem1p, involved in membrane trafficking and polarity establishment.

Purpose of the Study:

To investigate the direct binding capabilities of PX domains to phosphoinositides.
To elucidate the role of PX domains in protein localization to cellular membranes.

Main Methods:

In vitro binding assays to test interactions between purified PX domains and various phosphoinositides.
Expression of green fluorescent protein (GFP)-fused p40(phox) PX domain in HeLa cells to observe cellular localization.
Analysis of a mutant p40(phox) PX domain with a specific amino acid substitution (Lys for Arg105) to assess binding and localization defects.

Main Results:

PX domains of p40(phox) and p47(phox) directly bind to specific phosphoinositides: p40(phox) prefers PtdIns(3)P, while p47(phox) binds PtdIns(4)P and PtdIns(3,4)P(2).
The Bem1p PX domain also interacts with PtdIns(4)P.
In HeLa cells, the p40(phox) PX domain localizes to early endosomes, enriched in PtdIns(3)P.
A mutant p40(phox) PX domain exhibited weak phosphoinositide binding in vitro and failed to localize to early endosomes.

Conclusions:

The PX domain functions as a novel phosphoinositide-binding module.
This binding activity is crucial for targeting proteins to specific membrane compartments, such as early endosomes.
The findings suggest a general mechanism for membrane targeting mediated by PX domains in diverse cellular proteins.