Biophysical Society Thematic Meeting | Tutzing 2026

Single-Molecule FRET: The Next 30 Years

Thursday Speaker Abstracts

FRUSTRATED FLEXIBILITY SHAPES THE DYNAMICS OF CALMODULIN TRAPPING Narendar Kolimi 1,2 ; Rajen Goutam 1,3 ; M. Neal Waxham 4 ; Exequiel Medina 5 ; Hugo Sanabria 1 ; 1 Clemson University , Department of Physics and Astronomy , Clemson, SC, USA 2 University of Hyderabad, Department of Animal Biology, Hyderabad, India 3 North Carolina State University, Department of Physics, Raleigh, NC, USA 4 The University of Texas Health Science Center, Department of Neurobiology and Anatomy, Houston, TX, USA 5 Universidad de Chile, Department of Biochemistry and Molecular Biology, Santiago, Chile Calmodulin (CaM) is a ubiquitous calcium sensor that regulates diverse signaling pathways through its remarkable conformational plasticity. One of its most important interactions is with Ca² ⁺ /calmodulin-dependent protein kinase II (CaMKII), which can retain CaM after intracellular calcium levels decline through a process known as CaM trapping, a molecular mechanism central to synaptic plasticity and long-term potentiation. Despite decades of study, the dynamic structural basis underlying CaM trapping remains incompletely understood. Here, we combined single-molecule Förster resonance energy transfer (smFRET) with structural ensemble modeling to resolve the conformational landscape of CaM across its apo, calcium-bound, and CaMKII bound states. Using 11 strategically labeled CaM constructs, we observed inter- and intra-domain motions previously hidden from other structural approaches. smFRET measurements uncovered substantial conformational heterogeneity and dynamic fluctuations that persist even in the trapped state. We propose that CaM trapping emerges from a frustrated conformational landscape rather than from stabilization of a single rigid structure. These findings highlight the growing power of smFRET approaches to directly visualize dynamic biomolecular ensembles and transient states central to signaling regulation. More broadly, our work establishes conformational dynamics as central for CaM-mediated signaling, providing a framework for understanding how frustrated flexibility governs molecular recognition, memory formation, and allosteric regulation in complex biological systems.

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