Influence of the outer vestibule on permeation and gating in voltage-gated potassium channels

Voltage-gated potassium channels are potassium selective ion pores that open in response to membrane depolarization and close in response to hyperpolarization. In addition to their marked preference for potassium over other ions, these channels are noted for the impressive speed with which they move potassium through their ion conduction pathway. Decades of structural and functional studies have led to our current understanding of permeation and gating in voltage-gated channels. While the general mechanism of operation is agreed upon, the details that underlie the functional heterogeneity of structurally similar channels remain elusive. The outer vestibule of the Kv2.1 potassium channel undergoes a potassium-dependent conformational change. This structural reorientation, which appears unique to Kv2.1, is associated with changes in several basic channel functions. Here, we confirm the dynamic nature of the outer vestibule in this channel, and offer the first evidence for a mechanism of gating modulation whereby movement of a region in the pore influences the operation of the voltage sensor. We demonstrate that both the Kv2.1 and Kv 1.5 potassium channels possess unique features in their outer vestibules which endow them with an additional determinant of ionic selectivity, and possibly single channel conductance, located external to their selectivity filter region. Finally, the nature of TEA block in the outer vestibule of Kv2.1 and Shaker potassium channels is redefined as a more external, less direct coordination, and the implications of this for the understanding of slow inactivation are discussed. Together, the data presented in this dissertation advance the view that apparent differences in function among voltage-gated potassium channels reflect variations on a common mechanism of promoting selective, voltage-dependent ion flux. Specifically, these data indicate that the outer vestibule has a significant impact on many channel functions, and that differences in this structure alone may underlie many of the quantitative differences in permeation and gating of voltage-gated potassium channels.