Calcium-dependent conformational changes in inositol trisphosphate receptors

Area of Science:

• Biochemistry
• Molecular Biology
• Cellular Signaling

Background:

• Inositol trisphosphate receptors (IP3Rs) are intracellular calcium channels critical for cellular signaling.
• Understanding IP3R conformational dynamics in response to calcium is essential for elucidating their regulatory mechanisms.

Purpose of the Study:

• To investigate Ca(2+)-induced conformational changes of IP3Rs in their native membrane environment.
• To identify the specific domains and residues involved in these Ca(2+)-dependent structural alterations.

Main Methods:

• Limited trypsin digestion of IP3Rs in native membranes.
• Reactivity studies using PEG-maleimides (MPEG) to probe thiol accessibility.
• Site-directed mutagenesis of specific cysteine residues and domain deletion.

Main Results:

• Ca(2+) binding alters IP3R conformation, affecting trypsin cleavage sites and exposing endogenous thiols.
• Specific cysteine residues near transmembrane domains and the N-terminal suppressor domain are involved in Ca(2+)-dependent thiol reactivity.
• A C-terminal cysteine mutant showed altered accessibility to MPEG reagents, modulated by Ca(2+).

Conclusions:

• Significant Ca(2+)-induced conformational changes in IP3Rs can be detected in situ.
• Ca(2+) binding to the N-terminal suppressor domain likely exposes thiols in the channel domain.
• The C-terminal tail's accessibility to regulatory proteins is Ca(2+)-dependent.