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Jun-Yong Choe, PhD

Associate Professor
  • Iowa State University of Science and Technology, B.S. 1997, M.S. 1997, Ph.D. 2001
  • California Institute of Technology, Postdoc., 2002-2004
  • Structural Genomics Consortium, University of Toronto, Senior Crystallographer, 2004-2005
  • University of California Los Angeles, Assistant Research Physiologist, 2005-2007

Research

My main research interest is the structure-function relationship in membrane proteins and its application to drug discovery. Membrane proteins mediate the cell exchange of energy, nutrients and information. They are highly relevant to human physiology and disease (eg. depression, diabetes, multidrug resistance). Rational drug design relies on understanding the molecular basis of a protein’s function. Nevertheless, determination of the three-dimensional structure of membrane proteins continues to be an arduous task; less than 1% of their structures are known. I am particularly interested in secondary transport proteins, members of one of the largest membrane proteins superfamily, the Major Facilitator Superfamily (MFS). The structural technique of choice for MFS proteins is x-ray protein crystallography. In our laboratory, we apply high-throughput methodologies for protein expression and crystallization. Besides x-ray protein crystallography, we routinely use membrane protein biochemistry, molecular biology and structural modeling.

Glucose Transporters

Carbohydrates serve as basic fuel molecules for most cells. These molecules are unable to freely diffuse across cellular membranes but instead require dedicated transporter proteins to either enter or exit cells. In human cells the transport of glucose and related sugars is facilitated by a family of MFS transporters (SLC2 family) called glucose transporters (in short GLUTs). As key players in the availability of cellular energy source, GLUTs have been involved in various diseases including diabetes, cancer and the metabolic syndrome. For example, cancer cells because of their higher energy demands compared to healthy cells often express higher levels of GLUT proteins: GLUT1 (a transporter of glucose) is overexpressed in most cancers, GLUT5 (a transporter of fructose) is increased in breast cancer though normal breast cells lack GLUT5, other GLUTs are specifically increased in various cancers. Inhibitors of GLUT proteins can deprive cancer cells of energy and thus become a powerful tool in cancer eradication, especially when combined with a way to target tumor cells. My main research focus is to determine the molecular basis of differences in the function of GLUT members and to uncover new GLUT ligands that are specific for a certain GLUT member in order to facilitate drug discovery in GLUT-related diseases.

GLUT5-specific inhibitor, MSNBA, in the substrate binding cavity of GLUT5.
GLUT5-specific inhibitor, MSNBA, in the substrate binding cavity of GLUT5.

Salicylic Acid Storage in Plants

Salicylic acid (SA) is a plant hormone involved in regulating plant stress responses  including local and systemic pathogen responses. SA is stored as a glucose conjugate in the form of either an SA glucoside (SAG) or an SA glucose ester (SGE), and these conjugation reactions are catalyzed by glucosyltransferases. In the model organism Arabidopsis thaliana the enzyme UGT74F1 forms SAG while UGT74F2 primarily forms SGE however, UGT74F1 and UGT74F2 share 90% similarity at the amino acid level. Through structural biology, biochemistry and molecular biology, we aim to understand how SA is processed and stored in the plant cell.

Crystal structures of UGT74F2.  Overall structure with longitudinal section through the active site (left). Close-up of the active site showing binding site for UDP-glucose (right).
Crystal structures of UGT74F2.  Overall structure with longitudinal section through the active site (left). Close-up of the active site showing binding site for UDP-glucose (right).

Recent Publications

  • George Thompson, A.M., Iancu, C.V., Neet, K.E., Dean, J.V., and Choe, J. (2017) “Differences in substrate binding mode and catalytic mechanism lead to distinct salicylic acid glucose conjugates by UGT74F1 and UGT74F2 from Arabidopsis thaliana.” Scientific Reports 7, 46629.
  • George Thompson, A.M., Ursu, O., Iancu, C.V., Babkin, P, Oprea, T.I., and Choe, J. (2016) “Discovery of a specific inhibitor of human GLUT5 by virtual screening and in vitro transport evaluation.” Scientific Reports 6, 24240.
  • Jordan, P., Choe, J., Boles, E., and Oreb, M. (2016) “Hxt13, Hxt15, Hxt16 and Hxt17 of Saccharomyces cerevisiae represent a novel type of polyol transporters.” Scientific Reports 6, 23502.
  • Milton, M.E., Choe, J., Honzatko, R.B., Nelson, S.W. (2016) “Crystal structure of the apicoplast DNA polymerase from Plasmodium falciparum: the first look at an “atypical” A-family DNA polymerases.” Journal of Molecular Biology 428, 3920-3934.
  • Mandal, T., Shin, S., Aluvila, S., Chen, H.C., Grieve, C., Choe, J., Cheng, E. H., Hustedt, E. J., and Oh, K. J. (2016) “Assembly of Bak homodimers into higher order homooligomers in the mitochondrial apoptotic pore.” Scientific Reports 6, 30763.
  • Milton, M.E., Choe, J., Honzatko, R.B., Nelson, S.W. (2015) “Crystallization and preliminary X-ray analysis of the Plasmodium falciparum apicoplast DNA polymerase.” Acta Crystallogr. F Struct. Biol. Commun. 71, 333-337.
  • Babkin, P, George Thompson, A.M., Iancu, C.V., Walters, D.E., and Choe, J. (2015) “Antipsychotics inhibit glucose transport: determination of olanzapine binding site in Staphylococcus epidermidis glucose/H+ symporter.” FEBS OpenBio 5, 335–340.
  • George Thompson, A.M., Iancu, C.V., Nguyen, T.T.H. Kim, D., and Choe, J. (2015) “Inhibition of human GLUT1 and GLUT5 by plant carbohydrate products; insights into transport specificity.” Scientific Reports 5, 12804.
  • Choe, J. (2015) “Crystallography as Art: Revealing the Inner Workings of a Glucose Transporter.” Acad. Medicine 90, 1631.
  • Aluvila, S., Mandal, T., Hustedt, E., Fajer, P., Choe, J., Oh, K.J. (2014) “Organization of the Mitochondrial Apoptotic BAK Pore: Oligomerization of the BAK Homodimers.” J. Biol. Chem. 289, 2537-2551.
  • Gao, Y., Iancu, C.V., Mukind, S., Choe, J., and Honzatko, R.B. (2013) “Mechanism of Displacement of a Catalytically Essential Loop from the Active Site of Mammalian Fructose-1,6-bisphosphatase.” Biochemistry 52, 5206-5216.
  • Iancu, C.V., Zamoon, J., Woo, S.B., Aleshin, A., and Choe, J. (2013) “Crystal structure of a glucose/H+ symporter and its mechanism of action.” Proc Natl Acad Sci USA 110, 17862–17867.