Allostery in Ca²⁺ channel modulation by calcium-binding proteins.

Area of Science:

• Molecular and Cellular Biology
• Biophysics
• Neuroscience

Background:

• Distinguishing allosteric from competitive ligand binding is difficult, especially for large molecules.
• Calcium-binding proteins (CaBPs) are thought to compete with calmodulin (CaM) for binding to target molecules.
• The low abundance of CaBPs in the brain raises questions about their biological significance compared to CaM.

Purpose of the Study:

• To investigate the binding mechanism of CaBPs and CaM to calcium channels in live cells.
• To determine if CaBPs act allosterically or competitively in regulating CaM-mediated channel function.
• To develop a novel live-cell assay for studying holomolecule interactions.

Main Methods:

• Developed a live-cell, holomolecule approach by covalently linking CaM and/or CaBP4 to calcium channels.
• Utilized live-cell fluorescence resonance energy transfer (FRET) assays to monitor binding events.
• Resolved a cyclical allosteric binding scheme for CaM and CaBP4 on the calcium channels.

Main Results:

• Revealed an allosteric mechanism by which CaBP4 eliminates CaM-mediated inactivation of calcium channels.
• Demonstrated that CaBP4 binding induces conformational changes that prevent CaM-induced channel inactivation.
• Explained how even trace amounts of CaBPs can exert significant biological effects through allostery.

Conclusions:

• Calcium-binding proteins can regulate target molecules via allosteric mechanisms, challenging the prevailing competitive binding model.
• The developed live-cell holomolecule approach provides a powerful tool for dissecting allosteric interactions in their native cellular context.
• This study elucidates how low-abundance CaBPs can effectively modulate cellular signaling pathways.