The Voltage-dependent Calcium Channel Subunit Contains Two Stable Interacting Domains*

Voltage-dependent calcium channels selectively en-able Ca2 ion movement through cellular membranes. These multiprotein complexes are involved in a wide spectrum of biological processes such as signal trans-duction and cellular homeostasis. 1 is the membrane pore-forming subunit, whereas is an intracellular sub-unit that binds to 1, facilitating and modulating chan-nel function. We have expressed, purified, and charac-terized recombinant 3 and 2a using both biochemical and biophysical methods, including electrophysiology, to better understand the family’s protein structural and functional correlates. Our results indicate that the protein is composed of two distinct domains that as-sociate with one another in a stable manner. The data also suggest that the polypeptide regions outside thes