Date of Graduation

5-2013

Document Type

Dissertation

Degree Name

Doctor of Philosophy in Microelectronics-Photonics (PhD)

Degree Level

Graduate

Department

Graduate School

Advisor

Greg Salamo

Committee Member

Ralph Henry

Second Committee Member

William Oliver

Third Committee Member

Kaiming Ye

Fourth Committee Member

Ken Vickers

Abstract

Membrane transporters are a class of membrane proteins that function to provide a pathway across a cell membrane for the movement of ions and biomolecules. Investigations into the regulatory mechanism of these systems are hindered by their extensive preparation requirements compounded by their fragility and instability. However, lysenin, a pore-forming protein extracted from the earthworm Eisenia foetida, provided a unique opportunity to study a protein which is stable in both a soluble and membrane phase. Lysenin channels possess several important properties characteristic of ion channels without the inherent difficulties that plague investigations with biologically vital membrane transporters like voltage-gated ion channels.

Work described here focused on modeling and examining the dynamics of lysenin channels utilizing electrophysiological measurements and theoretical modeling to achieve an understanding of the structure and function of this pore-forming protein. This work investigated the response of the protein channel to an applied electric field which led to current rectification and hysteresis. The results of these studies were used to develop a model describing the mechanisms which give the channel its distinctive functionality. Moreover, the model supported predictions regarding channel behavior that were tested in response to changes in the environmental conditions.

This research uncovered the fascinating behavior exhibited by lysenin channels resultant from the dynamic equilibrium between the channel's two conductance states. It introduced a model that incorporated the influence of the lipid membrane on the protein channel. The results of these studies validated the model and supported the hypothesized theory as to the origins of channel gating. As a result, this work advanced the general understanding of the fundamental mechanisms of voltage-gated ion channels.

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