Conformational Changes in the Orai1 C-Terminus Evoked by STIM1 Binding

Area of Science:

• Cell Biology
• Molecular Biology
• Biophysics

Background:

• Store-operated calcium (SOC) entry, mediated by CRAC channels, is crucial for cellular functions like gene expression and proliferation.
• CRAC channels comprise Orai proteins (pore-forming) and STIM proteins (ER Ca2+ sensors).
• STIM1 activation involves migration to ER-PM junctions and direct interaction with Orai1 to open the channel.

Purpose of the Study:

• To investigate the conformational changes in Orai1 C-termini during STIM1 binding.
• To elucidate the role of Orai1 C-terminal self-association in CRAC channel regulation.

Main Methods:

• Site-directed mutagenesis of Orai1 C-termini.
• Chemical cross-linking to assess protein-protein interactions.
• Förster resonance energy transfer (FRET) to measure STIM1-Orai1 interaction dynamics.

Main Results:

• Disulfide cross-linking of Orai1 C-termini reduced STIM1-Orai1 interaction, indicating altered conformation.
• STIM1 binding to Orai1 C-termini impaired subsequent cross-linking of the C-termini.
• A specific bend (SHK sequence) in the Orai1 helix is essential for proper C-terminal orientation and STIM1 binding.

Conclusions:

• Orai1 C-termini undergo modest rearrangements to facilitate STIM1 binding.
• The self-associated Orai1 C-termini play a dynamic role in CRAC channel gating.
• Understanding these conformational dynamics offers insights into calcium signaling regulation.