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Volume 10, Issue 8 (Suppl) J Proteomics Bioinform, an open access journal
ISSN: 0974-276X Structural Biology 2017
September 18-20, 2017
9th International Conference on
Structural Biology
September 18-20, 2017 Zurich, Switzerland
Enrica Bordignon, J Proteomics Bioinform 2017, 10:8(Suppl)
DOI: 10.4172/0974-276X-C1-0100
Exploring conformational equilibria of a heterodimeric ABC transporter by electron paramagnetic
resonance
Enrica Bordignon
Ruhr-Universität Bochum, Germany
ABC exporters pump substrates across the membrane by coupling ATP-driven movements of nucleotide binding domains
to the transmembrane domains, which switch between inward and outward facing orientations. Understanding their
cycle has potential for medical applications because they are involved in multidrug resistance of cancer cells. Site-directed
spin labeling electron paramagnetic resonance and the dipolar spectroscopy technique called DEER or PELDOR was used
to investigate the conformational transition of the ABC heterodimeric exporter TM287/288 from the hyperthermophile T.
maritima. The analysis revealed that with nucleotides the transporter exists in an equilibrium between the IF and OF states.
ATP binding without hydrolysis was sufficient to partially populate the OF state, and an almost complete conformational shift
was observed when nucleotides were trapped in a pre-hydrolytic or post-hydrolytic state. At physiological temperature and
without nucleotides, the NBDs disengage asymmetrically while the conformation of the TMDs remains unchanged. Nucleotide
binding at the degenerate ATP site prevents complete NBD separation, a molecular feature differentiating heterodimeric ABC
exporters from their homodimeric counterparts. Our data suggest hydrolysis-independent partial closure of the NBD dimer,
which is further stabilized as the consensus site nucleotide is committed to hydrolysis. A unified mechanism is established,
which reconciles the available information for heterodimeric ABC exporters.
Biography
Enrica Bordignon is an Associate Professor at the Ruhr University of Bochum, where she leads an EPR laboratory dedicated to the study of membrane proteins.
She published approximately 50 papers in protein research by EPR methods. Her research interest is understanding the mechanism of action of proteins by EPR.
Figure1: Spin labeling sites in the extracellular,
intracellular and NBD regions of TM287/288,
represented in the inward-facing apo crystal
structure (PDB:4Q4H). TM287 is colored in cyan
and TM288 in pink.