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Orientational Texture of Lipid Bilayer and Monolayer Domains

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Orientational Texture of Lipid Bilayer and Monolayer Domains Orientational Texture of Lipid Bilayer and Monolayer Domains PhD Thesis Jes Dreier Supervised by Associate Professor Adam Cohen Simonsen MEMPHYS – center for biomembrane physics Department of1 Physics, Chemistry and Pharmacy MEMPHYS University of Southern Denmark ovember 2012 Preface his thesis covers the scientific work I have conducted during the last three year during my PhD education in biophysic at MEMPHYS – center for T biomembrane physics, Institute of Physics, Chemistry and Pharmacy, University of Southern Denmark. This work has been done under the qualified supervision of Associated Professor Adam Cohen Simonsen, and I am thankful for his help and advice during the last three years. Research Assistant Professor Jonathan R. Brewer should be acknowledged for the valuable help regarding the 2-photon microscope, its use, and interpretation of the results. I am very grateful to have had the opportunity to spend 6 month at University California Davis during my PhD. I owe many thanks to Professor Tonya Kuhl and Professor Margie Longo and their respectively research groups, for the help during my time there. I would like to acknowledge all the people at MEMPHYS for the help, support, and for making MEMPHYS what it is. A special thanks goes to the Ph.D. students Morten Christensen, Thomas E. Rasmussen and Mathias P. Clausen, both the help with this thesis, but also for countless discussions, (and much need coffee breaks) during my time at MEMPHYS. Your help have been invaluable. Most importantly a special thanks to my wife Signe, especially for the incredible support during the writing process of this thesis. The work in this thesis has lead to the following papers and manuscripts: J. Dreier, J. Brewer, and A.C. Simonsen, Texture Defects in Lipid Membrane Domains, Soft Matter, 2012, 8, 4894 J. Dreier, and A.C. Simonsen, Variations in the Hydrophobic Mismatch affects the Orientational Texture in Phospholipid Bilayers, (To be submitted) Front Page: Artistic image of the texture of several -domains in DOPC,DPPC bilayer. Finalist in the second Annual Biophysical Society Art of Science Image Contest, at the Biophysical Society 56th Annual Meeting 2012, San Diego, USA, I Abstract ateral organization of the cellular plasma membrane is of great importance in many cell processes, and is an exciting field to study. However, the L cellular plasma membrane is a very complex structure and consists of several thousands of unique components. By using supported lipid bilayers we are able to study phase separation, which is coupled to lateral organization, in a compositionally simpler model system that allow minute control of the variables. We study domains of phosphocholine lipids, which recently have been proven by polarized fluorescence microscopy and x-ray scattering to contain an internal orientational order of the lipid acyl chains. We measure this internal orientation order by polarized 2-photon fluorescence microscopy. The orientational texture, i.e. the description of the orientation and variation thereof across the entire domain, were found to be very complex. Lipid membranes of DOPC,DPPC formed domains that were divided into subdomains, each with a unique preferred orientation, Fig. (A). In the central region of the domains a vortex-like texture with a continuously change of orientation was observed, converging into two point defects (m = 1/2) in the center . By changing the lipid acyl chains, we were able to investigate the effect of the hydrophobic mismatch, i.e. the height difference between the and phases, on the orientational texture. For low hydrophobic mismatch (<1nm, POPC,DMPC) the complex orientational texture disappeared. Instead a uniform orientation was observed, see Fig. (B). Furthermore, it was found that the orientational texture was already present in small domains, close to the nucleation temperature. This texture was conserved during the further growth of the domain, meaning that the structures of the small domains are present in the larger domains at a lower temperature, seeFig. (C). AFM and polarized fluorescence microscopy were used to measure the orientational texture of LC-domains in monolayers of DLPC,DSPC. We proved that the change of temperature could affect the domain shape and orientational texture, Fig. (D). This was related to the non-isothermal growth of domains in the bilayer. II Sammenfatning en laterale organisation of den cellulære plasmamembran har stor betydning for mange af cellens processer. Dette gør den til et meget D spændende forskningsområde. Den cellulære plasmamembran er dog yderst compleks og består af flere tusinde forskellige komponenter. Vi bruger understøttede lipidmembraner, som er et simplere model system for den cellulære plasmamembran til at undersøge faseseparation, der er tæt koblet til den laterale organisering. Vi studerer domæner af fosfocholinlipider, som har vist sig at have en indre orienteringsorden af de lipide fedthaler. Dette er blevet vist med polariseret fluroscens mikroskopi og røntgen spredning. Vi måler denne indre orienteringsorden med polariseret 2-foton fluoresensmikroskopi. Den målte orienterings texturen, dvs. beskrivelsen af orienteringerne og hvordan de varierer i hele domænet, viste sig at være meget kompleks. Lipidmembraner af DOPC,DPPC dannede domæner, der var inddelt i subdomæner, hver med en unik foretrukken orientering, Fig. (A). I den centrale region af domænerne var der en kontinuerlig ændring af orienteringen. Den konvergerer ind til to punktdefekter (m = 1/2) i midten. Ved at ændre fedthalerne på lipiderne var vi i stand til at undersøge effekten af højdeforskellen mellem og faserne på orienteringsteksturen. For en lille højde forskel (<1nm, POPC,DMPC) forsvandt den complekse tekstur og blev erstattet af en uniform tekstur, Fig. (B). Den orienteringsmæssige tekstur var allerede til stede i små områder, tæt på nukleringstemperaturen. Under den videre dannelse af domænerne blev denne tekstur ikke ændret. Dette betyder, at teksturen af de små domæner er til stede i de større områder ved en lavere temperatur, se Fig. (C). AFM og polariseret fluorescensmikroskopi blev anvendt til at måle den orienteringsmæssige tekstur af LC-domæner i monolag af DLPC,DSPC. Ændringen af temperaturen påvirkede domænernes form og orienteringstekstur, Fig. (D). Dette var relevant for den ikke-isotermisk vækst af domæner i membranerne. III Abbreviations 2D = Two dimensions 3D = Three dimensions = Surface tension AFM = atomic force microscopy BAM = Brewster angle microscopy DLA = Diffusion limited aggregation DLPC = 1,2-dilauroyl-sn-glycero-3-phosphocholine DMPC = 1,2-dimyristoyl-sn-glycero-3-phosphocholine DOPC = 1,2-dioleoyl-sn-glycero-3-phosphocholine DPPC = 1,2-dipalmitoyl-sn-glycero-3-phosphocholine DSPC = 1,2-distearoyl-sn-glycero-3-phosphocholine G = Gaseous (monolayers phase) GIXD = gracing incidence x-ray diffraction GUI = Guide user interface GUV = giant unilamilar vesicles HWP = Half wave plate = Liquid crystalline/fluid/liquid disordered/LD (bilayer phase) = gel/solid ordered/SO(bilayer phase) LBS = Langmuir Blodgett-Schaeffer LE = Liquid expanded (monolayer phase) LC = Liquid condensed (monolayer phase) NA = numerical aperture PALM = photo-activated light microscopy PMT = photo multiplier tubes PC = phosphatidylcholine POPC = 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine QWP = quarter wave plate S = Solid (monolayer phase) SM-C18= N-stearoyl-D-erythro-sphingosylphosphorylcholine Sm-C = smectic- C (liquid crystal phase) SPM = scanning probe microscopy SPT = single particle tracking STED = stimulated emission depletion STORM = stochastic optical reconstructed microscopy SUV = small unilamilar vesicles Tm =Transition temperature IV Table of Content Preface I Abstract II Sammenfatning III Abbreviations IV Table of Content V 1 Chapter 1: Introduction ............................................................................................... 1 1.1 Lipids .......................................................................................................................... 1 1.2 Lateral Organization in the Cellular Membrane ..................................................... 4 1.3 Model System of a Plasma Membrane ...................................................................... 6 1.4 Motivation .................................................................................................................. 8 2 Chapter 2: Structural Order in 2 Dimensions ........................................................... 9 2.1 Phases and Phase Separation in Monolayers......................................................... 10 2.2 Liquid Crystals......................................................................................................... 13 2.3 The Hexatic Phases in Monolayers ......................................................................... 14 2.4 Phases and Phase Separation in Bilayers .............................................................. 23 3 Chapter 3: Fabrication and characterization ........................................................... 27 3.1 Fluorescence Microscopy ......................................................................................... 27 3.2 Laurdan .................................................................................................................... 29 3.3 Atomic Force Microscopy ......................................................................................... 32 3.4 Brewster Angle Microscopy ....................................................................................
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