A structure-based computational model of IP₃R1 incorporating Ca and IP3 regulation

Area of Science:

• Molecular Biology
• Biophysics
• Computational Biology

Background:

• The inositol 1,4,5-triphosphate receptor (IP3R) is crucial for cellular calcium (Ca) release, impacting diverse cellular functions.
• Structural studies of IP3R type 1 (IP3R1) reveal domain movements critical for channel gating, modulated by Ca and IP3 ligands.
• The precise mechanisms by which ligand-binding sites on IP3R1 interact to control channel opening remain unclear.

Purpose of the Study:

• To develop a computational model of IP3R1 that integrates channel architecture with Ca- and IP3-binding site locations.
• To investigate how ligand binding influences domain-domain interactions within and between IP3R1 subunits.
• To elucidate the interplay between Ca-binding sites and the IP3-binding site in regulating IP3R1 channel open probability.

Main Methods:

• Development of a coarse-grained computational model of the IP3R1 channel.
• Integration of known Ca- and IP3-binding site locations into the model.
• Application of a kinetic model to simulate ligand-binding effects on domain interactions and channel gating.
• Analysis of domain-domain interactions' role in channel cooperativity and Ca response.

Main Results:

• The model reveals how Ca and IP3 binding sites interact to control IP3R1 channel activity.
• The bell-shaped open probability of IP3R1 suggests constraints on the binding affinities of regulatory sites.
• A previously uncharacterized Ca-binding site is identified as a likely channel antagonist.
• Interactions between neighboring subunits significantly influence channel cooperativity and Ca-dependent responses.

Conclusions:

• Domain-domain interactions are vital for IP3R1 stability and function.
• The identified Ca-binding site's antagonistic role provides new insights into IP3R1 regulation.
• Disruptions in IP3R1 domain interactions may contribute to diseases involving calcium dysregulation.
• This computational approach offers a framework for understanding IP3R1 channel gating mechanisms.