Significant advancements in the field of membrane protein crystallography have provided in recent years invaluable images of transporter structures. These structures, however, are static and require complementary kinetic insight to understand how their mechanisms work. Electrophysiological studies of transporters permit the high quality kinetic measurements desired, but there are significant difficulties involved in analyzing and interpreting the data. Current methods allow a variety of kinetic parameters to be measured but there is a disconnect between these parameters and a fundamental understanding of the carrier. The intent of this research was to contribute new tools for studying the electrogenic kinetics of membrane transport proteins, to understand the link between these kinetics and the carrier, and to ultimately understand the mechanisms involved in transport. In this vein, two projects are explored covering two important kinetic time domains, transient and steady-state. The transient project studies the conformational changes of the unloaded carrier of SGLT1 through a multi-exponential analysis of the transient currents. Crystal structures have potentially identified a gated rocker-switch mechanism and the transient kinetics are used to support and study this kinetically. A protocol taking advantage of multiple holding potentials is used to measure the decay time constants and charge movements for voltage jumps from both hyperpolarizing and depolarizing directions. These directional measurements provide insight into the arrangement of the observed transitions through directional inequalities in charge movement, by considering the potential for a slow transition to hide a faster one. Ultimately, four carrier decays are observed that align with the gated rocker-switch mechanism and can be associated one-to-one with the movement of a gate and pore on each side of the membrane. The steady-state project considers a general theoretical model of transporter cycling. Recursive patterns are identified in the steady-state velocity equation that lead to a broad understanding of its geometric properties as a function of voltage and substrate concentration. This results in a simple phenomenological method for characterizing the I–V curves and for measuring the kinetics of rate limiting patterns in the loop, which we find are the basic structures revealed by the steady-state velocity.
| Identifer | oai:union.ndltd.org:LACETR/oai:collectionscanada.gc.ca:OTU.1807/32795 |
| Date | 31 August 2012 |
| Creators | Krofchick, Daniel |
| Contributors | Silverman, Mel |
| Source Sets | Library and Archives Canada ETDs Repository / Centre d'archives des thèses électroniques de Bibliothèque et Archives Canada |
| Language | en_ca |
| Detected Language | English |
| Type | Thesis |
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