Three-dimensional Structure of CaV3.1: COMPARISON WITH THE CARDIAC L-TYPE VOLTAGE-GATED CALCIUM CHANNEL MONOMER ARCHITECTURE

• Published in: The Journal of biological chemistry 2009-08, Vol.284 (33), p.22310-22321
• Main Authors: Walsh, Conor P, Davies, Anthony, Butcher, Adrian J, Dolphin, Annette C, Kitmitto, Ashraf
• Format: Article
• Language: English
• Subjects: Animals; Calcium Channels, L-Type - chemistry; Calcium Channels, T-Type - chemistry; Cattle; Crystallography, X-Ray - methods; Cytoplasm - metabolism; Heart - physiology; Insecta; Membrane Transport, Structure, Function, and Biogenesis; Models, Biological; Muscle, Skeletal - metabolism; Myocardium - metabolism; Peptides - chemistry; Protein Isoforms; Protein Structure, Tertiary; Rats
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1074/jbc.M109.017152

Calcium entry through voltage-gated calcium channels has widespread cellular effects upon a host of physiological processes including neuronal excitability, muscle excitation-contraction coupling, and secretion. Using single particle analysis methods, we have determined the first three-dimensional structure, at 23 Å resolution, for a member of the low voltage-activated voltage-gated calcium channel family, CaV3.1, a T-type channel. CaV3.1 has dimensions of ~115 x 85 x 95 Å, composed of two distinct segments. The cytoplasmic densities form a vestibule below the transmembrane domain with the C terminus, unambiguously identified by the presence of a His tag being ~65 Å long and curling around the base of the structure. The cytoplasmic assembly has a large exposed surface area that may serve as a signaling hub with the C terminus acting as a "fishing rod" to bind regulatory proteins. We have also determined a three-dimensional structure, at a resolution of 25 Å, for the monomeric form of the cardiac L-type voltage-gated calcium (high voltage-activated) channel with accessory proteins β and α₂δ bound to the ion channel polypeptide CaV1.2. Comparison with the skeletal muscle isoform finds a good match particularly with respect to the conformation, size, and shape of the domain identified as that formed by α₂. Furthermore, modeling of the CaV3.1 structure (analogous to CaV1.2 at these resolutions) into the heteromeric L-type voltage-gated calcium channel complex volume reveals multiple interaction sites for β-CaV1.2 binding and for the first time identifies the size and organization of the α₂δ polypeptides.