Allostery in Ca²⁺ channel modulation by calcium-binding proteins.
Distinguishing between allostery and competition among modulating ligands is challenging for large target molecules. Out of practical necessity, inferences are often drawn from in vitro assays on target fragments, but such inferences may belie actual mechanisms. One key example of such ambiguity concerns calcium-binding proteins (CaBPs) that tune signaling molecules regulated by calmodulin (CaM). As CaBPs resemble CaM, CaBPs are believed to competitively replace CaM on targets. Yet, brain CaM expression far surpasses that of CaBPs, raising questions as to whether CaBPs can exert appreciable biological actions. Here, we devise a live-cell, holomolecule approach that reveals an allosteric mechanism for calcium channels whose CaM-mediated inactivation is eliminated by CaBP4. Our strategy is to covalently link CaM and/or CaBP to holochannels, enabling live-cell fluorescence resonance energy transfer assays to resolve a cyclical allosteric binding scheme for CaM and CaBP4 to channels, thus explaining how trace CaBPs prevail. This approach may apply generally for discerning allostery in live cells.
Calcium Signals Laboratory, Department of Biomedical Engineering, The Johns Hopkins University School of Medicine, Baltimore, Maryland, USA.
Philemon S
PS
Yang
Calcium Signals Laboratory, Department of Biomedical Engineering, The Johns Hopkins University School of Medicine, Baltimore, Maryland, USA.
Manu Ben
MB
Johny
1] Calcium Signals Laboratory, Department of Biomedical Engineering, The Johns Hopkins University School of Medicine, Baltimore, Maryland, USA. [2] Department of Neuroscience, The Johns Hopkins University School of Medicine, Baltimore, Maryland, USA.
David T
DT
Yue
D000494:Allosteric Regulation; D001667:Binding, Competitive; D015220:Calcium Channels / Q000378:metabolism*; D002135:Calcium-Binding Proteins / Q000378:metabolism*; D002147:Calmodulin / Q000378:metabolism; D006801:Humans; D011485:Protein Binding; D015398:Signal Transduction
C514441:CABP4 protein, human; D015220:Calcium Channels; D002135:Calcium-Binding Proteins; D002147:Calmodulin