The Skaggs Institute
for Chemical Biology
Scientific Report 2005
Structural Biology of Transporters
G. Chang, A. Chen, Y. Chen, A.
Kariakin, X. He, O. Pornillos, C.L. Reyes, P. Szewczyk, S. Wada, A. Ward, Y. Yin, J. Yu
of the structure of the receptors and efflux transporters involved in multidrug resistance (MDR)
is an important and exciting frontier in both molecular structural biology and medicine. We are
interested in the structural basis for the transport of hydrophobic substrates across the cell
membrane by MDR transporters and signal transduction by receptors. We use several biophysical
techniques, including detergent/lipid protein chromatography, crystallization of membrane
proteins, and protein x-ray crystallography. Our experimental strategies include the overexpression,
large-scale purification, and 3-dimensional crystallization of these integral membrane proteins.
We have revealed the structures of several
structural conformations of MsbA, an MDR transporter from the ATP-binding cassette family. MsbA
is a bacterial homolog of human MDR1 (P-glycoprotein), which causes MDR in the treatment of cancer.
In collaboration with R. Milligan, Scripps Research, we are using electron cryomicroscopy to
study other possible conformational changes. Through the help of the Skaggs Institute, we are
expanding our structure determinations to incorporate mammalian ATP-binding cassette transporters
that confer the MDR phenotype as well as other ATP-binding cassette transporters that are involved
in human diseases, including cystic fibrosis, breast cancer, and macular dystrophy. In addition,
we are determining the x-ray structures of H+-drug antiporters from the major facilitator
superfamily, the multiple antimicrobial toxin extrusion family, and the small multidrug transporter
We are also solving the structure of membrane-bound
receptors that are important models for signal transduction across the lipid bilayer. Among the
families we are working on are the G proteincoupled receptors, which are pharmaceutically
important drug targets. Nearly all G proteincoupled receptors are predicted to have 7 transmembrane
helices with domains that bind ligand and activate G proteins. A structure of these receptors will
reveal the mechanisms of cell signaling on the molecular level.
Pornillos, O., Chen, Y.J., Chen,
A.P., Chang, G. X-ray structure of the EmrE multidrug transporter
in complex with a substrate. Science 310:1950, 2005.
Reyes, C.L., Chang, G.
Lipopolysaccharide stabilizes the crystal packing of the ABC transporter MsbA. Acta Crystallogr.
Reyes, C.L., Chang, G.
Structure of the ABC transporter MsbA in complex with ADPvanadate and lipopolysaccharide.
Science 308:1028, 2005.