Lateral Organization and Thermodynamics of Coiled-coil Lipopeptides - Implications for Docking and Fusion Efficiency
by Gesa Pähler
Date of Examination:2012-11-07
Date of issue:2013-01-24
Advisor:Prof. Dr. Andreas Janshoff
Referee:Prof. Dr. Andreas Janshoff
Referee:Prof. Dr. Ulf Diederichsen
Files in this item
Name:20130118_Dissertation Gesa Pähler_eDiss.pdf
Size:6.38Mb
Format:PDF
Abstract
English
Specific cellular membrane interaction is a crucial point in nature as it facilitates key processes like cell-cell communication or membrane fusion. The latter one is highly controlled frequently mediated by the superfamily of SNARE proteins (soluble N-ethylmaleimide-sensitive factor attachment protein receptor) in eukaryotic cells. The definite mechanism behind this process is still poorly understood, but the coiled-coil formation of the SNARE core complex consisting of four α-helices seems to generate the fusogenic driving force. This offers the possibility to design a straightforward experimental setup to mimic the complex protein-mediated membrane-membrane interaction by using mere protein fragments or peptides attached to artificial lipid bilayers, which self-assemble into a coiled-coil structure. In this work, three different sets of artificial coiled-coil forming peptides were synthesized and subsequently attached to maleimide containing phospholipids in membranes via an in situ coupling reaction generating a highly controllable functionalization protocol. Thus, secondary structure changes, kinetics as well as thermodynamic characteristics were monitored during coiled-coil formation in solution and on solid supported membranes with e.g. time-resolved ellipsometry, IR and CD spectroscopy. A distinct loss of entropy upon heterodimerization of peptides on surfaces was found. This could be correlated with a self-assembled lateral clustering of lipopeptides in membranes leading to translational immobilization of hybrid structures. Strikingly, these dense and highly ordered clusters, which act as obstacles for surrounding matrix lipids, undergo a slow but detectable reorganization process causing a partial dissolution of the found clusters upon coiled-coil formation. Furthermore, an increasing fusogenicity was shown, which was correlated to the degree of cluster formation. Upon focusing on energetic and as well structural characteristics, the established model system gives the possibility to screen the docking and fusion ability of different coiled-coil forming peptides leading to an ideal mimic for SNARE mediated membrane fusion.
Keywords: lipid bilayer; model membrane; clustering; fusion; peptides