Calcium-calmodulin regulation of sodium channel: structural competition, subtype-specific regulation and kinase-phosphatase modulation

Author

• Rita Fosuaa Gyawu, Mississippi State UniversityFollow

ORCID

https://orcid.org/0000-0003-1390-9558

Advisor

Johnson, Christopher

Committee Member

Fitzkee, Nicholas

Committee Member

Wipf, David

Committee Member

Olgar, Yusuf

Committee Member

Gangishetty, Mahesh

Date of Degree

5-15-2026

Original embargo terms

Embargo 2 years

Document Type

Dissertation - Open Access

Major

Chemistry

Degree Name

Doctor of Philosophy (Ph.D.)

College

College of Arts and Sciences

Department

Department of Chemistry

Abstract

Voltage-gated sodium (NaV) channels initiate and propagate action potentials in excitable cells, enabling neuronal signaling and cardiac muscle contraction. Inappropriate function of these channels can cause life-threatening diseases such as arrhythmia or seizures. Intracellular calcium (Ca²⁺) signaling modulates NaV channel function through the calcium sensor calmodulin (CaM), yet the molecular mechanisms by which CaM coordinates interactions among cytosolic channel domains, how these mechanisms vary across NaV subtypes, and how disease-associated CaM mutations disrupt this regulation have not been fully resolved. This work investigates calcium calmodulin regulation of NaV channels using an integrated structural, biophysical, and electrophysiological approach. Focusing on the cardiac NaV1.5 channel, the molecular interactions among the C-terminal domain (CTD), the IQ motif, the inactivation gate (IGATE), and CaM are defined. Using solution NMR spectroscopy and stopped-flow kinetics, it is demonstrated that previously proposed trimeric CTD-IQ motif-CaM complexes do not form in solution. Instead, CaM and CTD compete for the same binding site on the IQ motif. Calcium enhances CaM’s ability to sequester the IQ motif from the CTD, thereby promoting CaM IGATE engagement. Kinetic measurements further reveal domain-specific Ca²⁺ release, with the CaM N-lobe acting as a rapid calcium sensor and the C-lobe serving as a slower anchoring domain. Together, these findings revise prevailing “hand-off” models and establish a competitive, calcium-dependent interaction network governing NaV cytosolic regulation. These insights are extended across sodium channel subtypes by examining sequence variation at calmodulin binding site B of the inactivation gate. Comparative biophysical analyses of NaV1.2, NaV1.4, NaV1.5, and NaV1.6 IGATE peptides reveal 1:1 CaM binding with distinct thermodynamic properties and conformations. NaV1.2 forms a more ordered, enthalpy-driven complex, whereas NaV1.5 exhibits greater conformational flexibility and entropy. Functional studies using chimeric channels demonstrate that these differences tune calcium facilitated recovery from inactivation. Finally, it is shown that the disease-associated CaM mutation F89L alters NaV1.5 gating in a kinase and phosphatase dependent manner. These results suggest CaM as a critical integrator of calcium signaling and phosphorylation state, providing insights into how disrupted CaM regulation can lead to arrhythmia.

Recommended Citation

Gyawu, Rita Fosuaa, "Calcium-calmodulin regulation of sodium channel: structural competition, subtype-specific regulation and kinase-phosphatase modulation" (2026). Theses and Dissertations. 6905.
https://scholarsjunction.msstate.edu/td/6905