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p23/Tmp21 differentially targets the Rac-GAP beta2-chimaerin and protein kinase C via their C1 domains

Hongbin Wang1, Marcelo G Kazanietz

  • 1Department of Pharmacology, University of Pennsylvania School of Medicine, Philadelphia, PA 19104-6160.

Molecular Biology of the Cell
|February 19, 2010
PubMed

Insights

The protein p23/Tmp21 anchors C1 domain proteins, like beta2-chimaerin, to specific cellular locations. This protein-protein interaction is key for regulating protein compartmentalization and function.

Area of Science:

  • Cellular Biology
  • Molecular Signaling
  • Protein Interactions

Background:

  • C1 domains bind diacylglycerol and phorbol esters, mediating protein translocation to membranes.
  • The endoplasmic reticulum/Golgi protein p23/Tmp21 interacts with the C1 domain of alpha- and beta-chimaerins.
  • Diacylglycerol-regulated Rac-GTPase-activating proteins (GAPs) are involved in signaling pathways.

Purpose of the Study:

  • To investigate the role of p23/Tmp21 as a docking protein for C1 domain-containing proteins.
  • To elucidate the mechanism of perinuclear translocation of beta2-chimaerin mediated by p23/Tmp21.
  • To explore the differential interactions of C1 domains from various protein kinase C (PKC) isozymes with p23/Tmp21.

Main Methods:

  • Co-immunoprecipitation assays to study protein interactions.
  • Site-directed mutagenesis to identify key residues for binding.
  • Confocal microscopy to visualize protein localization within cells.

Main Results:

  • p23/Tmp21 acts as a docking protein, mediating the perinuclear translocation of beta2-chimaerin.
  • Specific residues (Glu227 and Leu248) in the beta2-chimaerin C1 domain are critical for p23/Tmp21 binding and targeting.
  • Isolated C1 domains from different PKC isozymes exhibit distinct interaction patterns with p23/Tmp21, with PKCepsilon's C1b domain showing specific binding that is disrupted by phorbol esters.

Conclusions:

  • p23/Tmp21 serves as a distinct anchor modulating the compartmentalization of C1 domain proteins.
  • p23/Tmp21 plays a crucial role in the relocalization of beta2-chimaerin.
  • C1 domains are important for protein-protein interactions beyond their known lipid-binding functions.

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