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John Katsaras
Principal Research Officer
BA (Concordia, Montreal) BSc (Concordia, Montreal) MSc (Guelph) PhD (Guelph) PDF (McMaster, Hamilton; CNRS/CRPP, Bordeaux, France)
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CONTACT INFORMATION
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Address: Canadian Neutron Beam Centre Steacie Institute for Molecular Sciences National Research Council Chalk River Laboratories Bldg. 459, Stn 18 Chalk River, ON K0J 1J0 E-Mail: John.Katsaras@nrc-cnrc.gc.ca Phone: 1-613-584-8811 Ext. 43984 FAX: 1-613-584-4040 |
APPOINTMENTS
Principal Research Officer:
Adjunct Professor of Physics:
Biophysics Interdepartmental Group
Guelph-Waterloo Physics Institute
RESEARCH INTERESTS
Katsaras’ primary area of research is soft condensed matter physics, in particular, the structural determination of biologically relevant systems and their interactions through the use of appropriate scattering techniques (i.e. neutrons, x-rays and light).
Current interests include: (1) The development of spontaneously forming, functionalised unilamellar vesicles specifically targeted to delivering payloads to the brain; (2) The detailed structure of biofilms; (3) Atomic resolution neutron and x-ray holographies.
RESEARCH DEVELOPMENTS
THE FUNCTIONAL SIGNIFICANCE OF LIPID DIVERSITY:
ORIENTATION OF CHOLESTEROL IN BILAYERS IS DETERMINED BY LIPID SPECIES
J. Am. Chem. Soc. 131, 16358 (2009)
Harroun et al. [Biochemistry 45, 1227 (2006); Biochemistry 47, 7090 (2008)] have previously showed that cholesterol is sequestered in the bilayer center of polyunsaturated fatty acid (PUFA) bilayers. Consistent with this result, we observed the same location for cholesterol in PUFA bilayers doped with small amounts of POPC. Figure 1A shows the NSLD difference profile corresponding to PUFA bilayers containing 30 mol % POPC, in which the cholesterol label was clearly observed in the bilayer center. This was the highest POPC concentration in which cholesterol was unambiguously observed in the bilayer center. However, the situation changed with increasing amounts of POPC. Figure 1B shows the NSLD difference profile for PUFA bilayers containing 50 mol % POPC, the lowest concentration at which we observed cholesterol to revert to its upright orientation. The deuterium label appears to be approximately 15 Å from the bilayer center, placing cholesterol’s hydroxyl group within the bilayer’s hydrophobic/hydrophilic interfacial region, in excellent agreement with previous data.
The situation when doping PUFA bilayers with DMPC is, however, dramatically different from that with POPC. While 50 mol % POPC was necessary to flip cholesterol into its upright position in PUFA bilayers, Figure 2 shows that only 5 mol % DMPC was necessary to achieve the same effect. This result clearly demonstrates cholesterol’s affinity for saturated chains. For further details please see: J. Am. Chem. Soc. 131, 16358 (2009)
Figure 1. Neutron scattering length density difference profiles (deuterated minus nondeuterated
cholesterol) showing the distribution of cholesterol’s deuterium label in (A)
30 and (B) 50 mol % POPC-doped PUFA bilayers. Cartoons depict a
schematic view of the various bilayer components, with POPC in yellow,
PUFA in green, cholesterol in purple, and deuterium label in black.
AFMNet
The $22 million Advanced Foods and Materials Network (AFMNet), funded by the Networks of Centres of Excellence, is Canada’s front line of research and development in the area of advanced foods and bio-materials – from cancer-fighting tomatoes, to rubber made from sunflowers, to cleaner pulp and paper mills.
CANADIAN BIOPHYSICS
For information about Canadian Biophysics please visit Andrew Rutenberg's (Dalhousie University) site of Canadian Biophysicists.
