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Mutagenesis and Functional Analysis of Ion Channels Heterologously Expressed in Mammalian Cells
15:28

Mutagenesis and Functional Analysis of Ion Channels Heterologously Expressed in Mammalian Cells

Published on: October 1, 2010

N-terminal tyrosine residues within the potassium channel Kir3 modulate GTPase activity of Galphai

Danielle L Ippolito1, Paul A Temkin, Sherri L Rogalski

  • 1Department of Pharmacology, University of Washington School of Medicine, Seattle, Washington 98195-7280, USA.

The Journal of Biological Chemistry
|June 26, 2002
PubMed

Insights

Brain-derived neurotrophic factor (BDNF) activates trkB receptors, accelerating Kir3 channel deactivation by enhancing GTPase activity. This mechanism involves tyrosine phosphorylation of Kir3, revealing its GTPase-activating protein (GAP) domain.

Area of Science:

  • Neuroscience
  • Molecular Biology
  • Ion Channel Physiology

Background:

  • trkB receptor activation by BDNF leads to tyrosine phosphorylation of Kir3 channels, reducing their activity.
  • The precise mechanism by which BDNF/trkB signaling affects Kir3 channel function remains unclear.

Purpose of the Study:

  • To elucidate the molecular mechanism underlying BDNF-mediated inhibition of Kir3 channels.
  • To investigate the role of tyrosine phosphorylation and GTPase activity in this process.

Main Methods:

  • Reconstitution of Kir3, trkB, and mu opioid receptor in Xenopus oocytes.
  • Assessment of Kir3 deactivation kinetics following mu opioid receptor signaling termination.
  • Manipulation of GTPase activity using GTPgammaS and overexpression of RGS4.
  • Inhibition of tyrosine phosphatases with peroxyvanadate.
  • Site-directed mutagenesis of Kir3.4 N-terminal tyrosine residues.

Main Results:

  • BDNF activation of trkB accelerated Kir3 deactivation, mimicking RGS4 overexpression.
  • GTPgammaS blocked Kir3 deactivation, and this effect was not reversed by BDNF.
  • Tyrosine phosphatase inhibition mimicked the BDNF effect, suggesting a role for tyrosine phosphorylation.
  • Mutation of N-terminal tyrosines in Kir3.4 abolished the BDNF-induced acceleration of deactivation.

Conclusions:

  • BDNF/trkB signaling inhibits Kir3 channels by accelerating GTPase activity, likely through tyrosine phosphorylation of Kir3.
  • Phosphorylation or mutation of N-terminal tyrosines unmasks the channel's intrinsic GTPase-activating protein (GAP) domain.
  • This mechanism facilitates Kir3 channel deactivation, providing a novel pathway for neuronal signaling modulation.

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