Dynamics and Energetics of Secondary-Active Glutamate Transport

Suny At Binghamton, Binghamton NY

Investigators

Abstract

The plasma membrane separates the interior of the cell from the extracellular space and provides a barrier to cell entry/exit for many molecules (for example nutrient or signaling molecules) that are essential for cell survival. Glutamate is one such molecule, which is not only an amino acid needed for the synthesis of proteins, but also the most important neurotransmitter in the mammalian brain, responsible for the majority of excitatory neurotransmission. Glutamate is transported across the plasma membrane through active glutamate transporters, which play essential roles in controlling the levels of glutamate in the mammalian brain and other tissue. This project explores the fundamental principles by which these transporters work. Understanding these principles is important because it will contribute to our knowledge not only of the role of glutamate and nutrient movement between cellular compartments in the mammalian brain, as well as other organs of the body, but also glutamate homeostasis, which is important for cellular function in general. Furthermore, the developed methods for analyzing transport will be applicable to potential future studies of other neurotransmitter and/or nutrient transporters and membrane proteins. On the educational level, the project provides an invaluable opportunity for undergraduate students to become involved in cutting-edge biophysical research, providing training in basic physical, quantitative approaches to be applied to a significant biological problem. The investigator is continuing previous efforts of undergraduate involvement (including members of under-represented groups), which has led to many publications with undergraduate students as co-authors, as well as students successfully moving on to careers in research. The investigator is also very active in local and regional activities that promote the sciences at all levels, including demonstrations at schools, science fair involvement, and assuming leadership roles in the local American Chemical Society (ACS) section and the Science Olympiad. Such activities are necessary to ensure a vibrant local science community and to foster excitement of the upcoming generations of young scientists for science and research. Active glutamate transport is a multi-step process that requires multiple ion/substrate binding steps, as well as conformational changes. Despite recent progress towards understanding the transport process through functional studies, as well as the identification of structural models of a bacterial homologue of mammalian glutamate transporters in several states, basic questions about the mechanism, specificity, and dynamics of interaction of the transporters with cations, in particular K+ and Li+, as well as the energetic contributions to energy barriers that control the transport rate and specific structural changes in the transport cycle remain unresolved. Answers to these questions are obtained by applying a combination of experimental and computational methods, allowing the investigation of the dynamics of glutamate transport in real time, with microsecond time resolution, and to test predictions from all-atom and simplified molecular models. This work has the potential to reveal new aspects of glutamate movement across the cellular membrane, in particular with respect to the cooperation of polar and non-polar forces, which are fine tuned to adjust the energy barriers associated with ion/substrate binding, as well as conformational changes. The novel insight may uncover more general concepts that are employed by membrane transport proteins, in order to provide a permeation pathway for polar molecules across the hydrophobic membrane.