Katherine Henzler-Wildman

Photo of Katherine Henzler-Wildman
Associate Professor
Ph.D. in Chemistry, University of Michigan
Phone: (608) 890-1094
Email: henzlerwildm@wisc.edu

Dynamics and Function of Integral Membrane Proteins

image of Dr. Katherine Henzler-Wildman researchMany membrane proteins are active molecules that move molecules or relay signals across membrane barriers. To fully understand the function of these proteins, not only the structure, but the timescale, amplitude, and directionality of structural changes must be determined. We use NMR as our primary technique to monitor protein structure and dynamics, taking advantage of the extensive resources available through NMRFAM. By comparing our NMR data with biochemical and functional assays, we gain insight into the mechanisms of substrate transport, multidrug recognition, ion channel gating and ion selectivity.

image of titration resultsSecondary Active Transport

Protein conformational change is required for active transport, allowing alternating access to either side of the membrane in order to move a substrate against its electrochemical gradient. In the case of secondary transporters, the energy source for this process is the “downhill” flow of a second substrate, often protons.  Our research investigates the protein dynamics central to the transport process and the critical coupling between substrates used to drive net transport.

We are currently studying the small multidrug resistance transporter, EmrE, one of the smallest known active transporters. EmrE functions as a homodimer, pumping polyaromatic cations out of E. coli and conferring resistance to drugs matching this chemical description. The cartoon presents a model of the conformational changes believed to occur during the EmrE transport cycle. Our research focuses on three broad questions: How does such EmrE recognize and actively transport such a diverse set of substrates? How is drug efflux coupled to proton import? What are the key structural and dynamic features required for active transport? How does the lipid environment affect EmrE structure, dynamics, and transport?

A second project examines the GLUT family of eukaryotic sugar transporters. The GLUTs have play an important role transporting glucose across the plasma membrane into mammalian cells. Our goals are to develop the NMR and biochemical tools needed to tackle large, challenging eukaryotic membrane proteins and gain insight into the mechanism of glucose transport in humans.

Ion Channels

Small bacterial ion channels serve as simplified model systems for dissecting the molecular mechanisms underlying fundamental channel properties, such as ion selectivity and channel gating. The NaK channel is a non-selective cation channel from Bacillus cereus that can be converted to a potassium-selective channel with two point mutations. The very high quality of NaK NMR spectra and availability of multiple high-resolution crystal structures make it an ideal system to study how ion selectivity arises from the atomic-resolution structure and dynamics of the channel.