Solution structure of the NaV1.2 C-terminal EF-hand domain

Area of Science:

• Structural biology
• Molecular neuroscience
• Ion channel biophysics

Background:

• Voltage-gated sodium channels (NaV) are crucial for action potential generation in excitable cells.
• Mutations in intracellular C-terminal regions of NaV channels are linked to channelopathies like cardiac arrhythmias and epilepsy.
• Understanding the structure of these C-terminal domains is key to elucidating disease mechanisms.

Purpose of the Study:

• To determine the three-dimensional structure of the C-terminal domain of the human NaV1.2 voltage-gated sodium channel.
• To investigate the calcium (Ca2+) binding properties of the NaV1.2 C-terminal domain.
• To map the location of clinically significant mutations within the determined structure.

Main Methods:

• Nuclear Magnetic Resonance (NMR) spectroscopy was used to determine the structure of NaV1.2 (residues 1777-1882) in solution.
• 1H,15N chemical shift analysis was performed during Ca2+ titration to assess binding.
• Similar methods were applied to the NaV1.5 (residues 1773-1878) isoform.

Main Results:

• The ordered structure of NaV1.2 C-terminal domain (residues 1790-1868) comprises four alpha-helices and two anti-parallel beta-strands.
• A less defined helical region and a disordered N-terminal region were also identified.
• Ca2+ titration experiments revealed no binding to the canonical EF-hand loops in both NaV1.2 and NaV1.5 isoforms.
• Clinically relevant mutations cluster in specific interfacial and interhelical regions, as well as helices III and IV.

Conclusions:

• The NaV1.2 C-terminal domain adopts a specific fold but does not bind Ca2+ via EF-hand motifs.
• The structural data provides a framework for understanding how mutations in this region lead to channelopathies.
• Mapping mutation sites onto the structure offers insights into the molecular basis of associated diseases.