X-ray Crystal Structure and Transport Mechanism of a Na+/galactoside Symporter

Texas Tech University Health Science Center, Lubbock TX

Investigators

Abstract

INTELLECTUAL MERIT The membranes of living cells develop electrochemical energy that provides a critical mechanism for numerous cell functions. Proteins inserted in the membrane act like batteries and use the energy to move molecules in or out of the cell, making the chemical composition appropriate for normal cell function. The membrane protein called melibiose permease (MelB), present in certain bacteria, couples the transport of a sodium ion with a sugar (melibiose) molecule into the cell. In fact, it uses the favorable energy for sodium entry to build a high sugar concentration in the cell. A MelB human homologue is widely expressed in many tissues and has been found to be physiologically important. There are many proteins that work similarly, yet the precise mechanisms are not understood. The three-dimensional structure of MelB (at the atomic level) will constitute a breakthrough essential for the understanding of the molecular mechanism of transport. This project aims to obtain the high-resolution crystal structure of MelB by X-ray crystallography and to identify the specific amino acids in the protein responsible for selecting melibiose and sodium ion. This will be done by generating mutant proteins and testing their function with quantitative biochemical and biophysical methods. The results from this research will add crucial information to the understanding of how a membrane protein converts ionic energy to move sugar or other nutrients into a cell. BROADER IMPACTS This project will provide a platform to foster the integration of cutting-edge research and higher education by recruiting and motivating undergraduate students to pursue careers in basic science and by helping them develop technical skills and passion towards experimental science. Minorities constitute 20% of TTU undergraduate students. A particular effort will be made to recruit and provide research opportunities to these students. Graduate education and postdoctoral training are critical for science of tomorrow. This research will also offer rich training and educational opportunities to graduate students, to gain solid knowledge and experiential skills necessary for success in research, and for postdoctoral fellows to further their education and experimental armamentarium to become productive independent investigators. The outcome of the research will be disseminated timely and broadly through high-impact scientific papers, book chapters, course materials, invited lectures, and presentations at scientific meetings or interdisciplinary conferences to reach broad audiences. The expected high-resolution structure will be deposited in the open-access Protein Data Bank for broader application. This project is jointly supported by the Cellular Processes Cluster in the Division of Molecular and Cellular Biosciences and the Chemistry of Life Processes program in the Chemistry Division.