Tuesday, May 3, 2016
1:15 pm, MRB 200 Conference Room
Dr. David S. Cafiso
Department of Chemistry and Center for Membrane Biology, University of Virginia
Two-Way Transmembrane Signaling in an Outer-Membrane Transport Protein: what spectroscopy can tell us that crystal structures cannot
Proteins execute motion over a wide range of amplitudes and time scales, which may include large amplitude movements between discrete structural substates. A change in the equilibrium distribution of these substates is thought to underlie protein allostery and to play a role in mediating protein-protein recognition. Site-directed spin labeling when combined with EPR spectroscopy is one of the best methods to examine conformational exchange and structural heterogeneity in globular, membrane proteins and protein complexes. In TonB-dependent transporters, such as the Escherichia coli vitamin B12 transporter BtuB, EPR spectroscopy demonstrates that substrate binding promotes an unfolding of an energy-coupling motif at the periplasmic interface to up-regulate binding to the inner membrane protein TonB. In addition, TonB binding is found to alter the dynamics of the extracellular loops and to raise the energy of the substrate at the extracellular binding site. This two-way allosteric communication is likely a key feature underlying the transport mechanism in this family of transporters.