SOAR and the polybasic STIM1 domains gate and regulate Orai channels.

Area of Science:

• Cellular Biology
• Molecular Biology
• Biochemistry

Background:

• Store-operated calcium (SOC) channels, like Orai, are critical for receptor-evoked calcium signals.
• The endoplasmic reticulum (ER) calcium sensor STIM1 gates Orai channels, but the precise gating mechanism remains elusive.

Purpose of the Study:

• To elucidate the molecular basis by which STIM1 gates Orai channels.
• To identify the specific regions of STIM1 and Orai involved in channel activation and regulation.

Main Methods:

• Site-directed mutagenesis of STIM1 and Orai1.
• Analysis of STIM1-Orai1 interactions and co-clustering.
• Functional characterization of Orai channel gating kinetics.

Main Results:

• A conserved STIM1 fragment (344-442), termed SOAR, directly activates Orai channels.
• Mutations within SOAR abolish Orai1 activation but not STIM1-Orai1 co-clustering, indicating clustering is insufficient for gating.
• Specific regions in both STIM1 and Orai1 C-terminus and N-terminus are essential for channel activation and rectification.

Conclusions:

• The SOAR domain of STIM1 is the primary determinant for Orai channel activation.
• Orai channel gating by STIM1 involves specific molecular interactions beyond simple co-clustering.
• Understanding these interactions provides insight into calcium signaling regulation and potential therapeutic targets.