Structure and Function of Voltage-Dependent Ion Channel Regulatory β Subunits

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Abstract
Voltage-dependent K+, Ca2+, and Na+ channels play vital roles in basic physiological processes, including management of the action potential, signal transduction, and secretion. They share the common function of passively transporting ions across cell membranes; thus, it would not be surprising if they should exhibit similarities of both structure and mechanism. Indeed, the principal pore-forming (α) subunits of each show either exact or approximate 4-fold symmetry and share a similar transmembrane topology, and all are gated by changes in membrane potential. Furthermore, these channels all possess an auxiliary polypeptide, designated the β subunit, which plays an important role in their regulation. Despite considerable functional semblences and abilities to interact with structurally similar α subunits, however, there is considerable structural diversity among the β subunits. In this review, we discuss the similarities and differences in the structures and functions of the β subunits of the voltage-dependent K+, Ca2+, and Na+ channels.
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