Molecular Determinants for STIM1 Activation During Store- Operated Ca2+ Entry

Area of Science:

• Molecular Cell Biology
• Calcium Signaling

Background:

• Store-operated calcium entry (SOCE) is crucial for cellular functions, mediated by STIM1 and ORAI1 proteins.
• Dysfunctional STIM1/ORAI1 causes severe combined immunodeficiency and tubular aggregate myopathy.
• STIM1 activation, triggered by low ER calcium, involves luminal domain multimerization and ORAI channel gating.

Purpose of the Study:

• To systematically investigate the molecular determinants governing STIM1 activation and oligomerization.
• To utilize a fluorescence resonance energy transfer (FRET) assay to monitor STIM1 intramolecular autoinhibition.

Main Methods:

• Employing FRET assays to track STIM1 intramolecular dynamics.
• Utilizing domain truncations and substitutions to assess STIM1 functional domains.
• Investigating the role of the transmembrane (TM) domain in STIM1 activation.
• Analyzing hetero-oligomerization between full-length STIM1 and the SOAR region.

Main Results:

• Truncation of the STIM1 luminal domain promotes a more active STIM1 conformation.
• Replacing the native TM domain with a rigid glycophorin A TM domain inhibits STIM1 activation.
• Disrupting the TM dimerization interface partially restores STIM1 activation.
• Identified critical regions for hetero-oligomer assembly between STIM1 and SOAR.

Conclusions:

• Major STIM1 functional domains play essential roles in maintaining its quiescent state.
• Understanding these domains is key to preventing preactivation of SOCE.
• This research clarifies STIM1's regulatory mechanisms in calcium signaling.