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Activation of STIM1-Orai1 involves an intramolecular switching mechanism

Marek K Korzeniowski1, Isabel Martín Manjarrés, Peter Varnai

  • 1Section on Molecular Signal Transduction, Program for Developmental Neuroscience, National Institute of Child Health and Human Development, Bethesda, MD 20892, USA.

Science Signaling
|November 18, 2010
PubMed

Insights

Stromal interaction molecule 1 (STIM1) regulates calcium (Ca2+) influx by interacting with Orai1 channels. An acidic motif in STIM1 acts as an intramolecular clamp, keeping the Orai1-activating domain inactive until released.

Area of Science:

  • Cellular Biology
  • Molecular Biology
  • Biochemistry

Background:

  • Stromal interaction molecule 1 (STIM1) is a key regulator of store-operated calcium entry.
  • STIM1 senses calcium levels in the endoplasmic reticulum and signals to Orai1 channels in the plasma membrane.
  • Orai1 channels mediate calcium influx crucial for various cellular functions.

Purpose of the Study:

  • To elucidate the molecular mechanism by which STIM1 is activated.
  • To identify the structural elements within STIM1 responsible for Orai1 channel regulation.
  • To understand the intramolecular regulation of the STIM1 Ca2+ release-activated Ca2+ (CRAC) activation domain/STIM1-Orai activating region (CAD/SOAR).

Main Methods:

  • Site-directed mutagenesis of STIM1.
  • Biochemical assays to assess STIM1-Orai1 interaction and channel activity.
  • Analysis of conserved motifs within the STIM1 coiled-coil region.

Main Results:

  • An acidic motif within the STIM1 coiled-coil region was identified as an intramolecular inhibitor of the CAD/SOAR domain.
  • Mutations in the acidic motif led to constitutive activation of STIM1 and Orai1.
  • Mutations in a basic segment of the CAD/SOAR domain abolished Orai1 activation.
  • The acidic motif shares sequence similarity with the Orai1 carboxyl-terminal coiled-coil segment.

Conclusions:

  • STIM1 activation involves the release of an intramolecular clamp, allowing the CAD/SOAR domain to interact with and activate Orai1 channels.
  • This mechanism is conserved and analogous to pseudosubstrate regulation in protein kinases.
  • The findings provide a detailed molecular model for STIM1-mediated calcium influx regulation.

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