Title

Control of outer vestibule conformation and function in voltage-gated potassium channels

Date of Completion

January 2005

Keywords

Biophysics, General

Degree

Ph.D.

Abstract

Voltage-gated potassium channels are a family of integral membrane proteins, which possess single file pores and demonstrate a significant selectivity for potassium compared to other monovalent cations. They open following membrane depolarization and close with membrane hyperpolarization. Despite several similarities, a striking feature of these channels is the degree of diversity that they show in their molecular structure, which allows them to gain specific functional properties. Kv2.1 is a member of the voltage-gated potassium channel family that shows a potassium-dependent conformational change in its outer vestibule. This conformational reorientation appears to influence multiple channel functions like activation, inactivation and the ability to be blocked by toxins and pharmacological agents. Here, we demonstrate the factors which contribute to regulation of this outer vestibule movement and present evidence for the critical role of potassium concentration in controlling of this reorientation. The data demonstrates that this conformational change is almost entirely responsible for changes in current magnitude in response to fluctuation of potassium concentration in the extracellular solution. Furthermore, we perform experiments that support a potassium-dependent conformational change in the outer vestibule of another potassium channel, Kv1.5. Later, we provide evidence that suggests the location of the external TEA in the outer vestibule of Kv2.1 and Shaker potassium channels, is more external compared to where it was classically believed to be and we discuss how this finding affects our understanding of slow inactivation. Finally, through performing a series of experiments, we propose that upon activation, a conformational change near the selectivity filter in the outer vestibule of Kv2.1 occurs. This movement influences the way cations and anions access the outer mouth of the selectivity filter in different channel states. Altogether, the data presented in this dissertation demonstrate how changes in the outer vestibule structure of voltage-gated potassium channels impact multiple channel functions. In addition, it improves our overall understanding of underlying factors that regulate this movement. ^