tailieunhanh - Báo cáo khoa học: An X-ray diffraction study of model membrane raft structures

Protein sorting and assembly in membrane biogenesis and function involves the creation of ordered domains of lipids known as membrane rafts. The rafts are comprised of all the major classes of lipids, including glycero-phospholipids, sphingolipids and sterol. Cholesterol is known to interact with sphingomyelin to form a liquid-ordered bilayer phase. | ỊFEBS Journal An X-ray diffraction study of model membrane raft structures Peter J. Quinn1 and Claude Wolf2 1 Biochemistry Department King s College London UK 2 ER7-Faculte de Medecine-UPMC APLIPID Universite Paris 6 France Keywords lipid rafts liquid-ordered phase membrane rafts sphingomyelin X-ray diffraction Correspondence P. J. Quinn Biochemistry Department King s College London 150 Stamford Street London SE1 9NH UK Fax 442078484500 Tel 442078484408 E-mail Received 6 July 2010 revised 1 September 2010 accepted 9 September 2010 doi Protein sorting and assembly in membrane biogenesis and function involves the creation of ordered domains of lipids known as membrane rafts. The rafts are comprised of all the major classes of lipids including glycero-phospholipids sphingolipids and sterol. Cholesterol is known to interact with sphingomyelin to form a liquid-ordered bilayer phase. Domains formed by sphingomyelin and cholesterol however represent relatively small proportions of the lipids found in membrane rafts and the properties of other raft lipids are not well characterized. We examined the structure of lipid bilayers comprised of aqueous dispersions of ternary mixtures of phosphatidylcholines and sphingomyelins from tissue extracts and cholesterol using synchrotron X-ray powder diffraction methods. Analysis of the Bragg reflections using peak-fitting methods enables the distinction of three coexisting bilayer structures a a quasicrystalline structure comprised of equimolar proportions of phosphatidylcholine and sphingomyelin b a liquid-ordered bilayer of phospholipid and cholesterol and c fluid phospholipid bilayers. The structures have been assigned on the basis of lamellar repeat spacings relative scattering intensities and bilayer thickness of binary and ternary lipid mixtures of varying composition subjected to thermal scans between 20 and 50 C. The results suggest that the order created by the .