Solid Supported Model Membranes Containing Plant Glycolipids: A Tool to Study Interactions between Diatom Biomolecules and the Silicalemma in vitro
by Oliver Gräb
Date of Examination:2017-06-13
Date of issue:2017-06-22
Advisor:Prof. Dr. Claudia Steinem
Referee:Prof. Dr. Claudia Steinem
Referee:Prof. Dr. Daniel John Jackson
Referee:Prof. Dr. Burkhard Geil
Referee:Prof. Dr. Bert De Groot
Referee:Dr. Jochen Hub
Referee:Dr. Sebastian Kruss
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Description:Dissertation
Abstract
English
Silica biomineralization in diatoms is presumably controlled by a self-assembly of biomolecules inside membrane-enclosed silica deposition vesicles. The fine-patterned structure of the diatom’s cell wall is thereby determined by the morphology of the templating organic matrix. Several studies addressed self- or co-aggregation of silica-associated biomolecules in solution but no research focusing on the influence of the organelle surrounding lipid bilayer was published so far. This study aimed on the investigation of interactions between exemplary diatom biomolecules and lipid membranes in vitro. As a basis for all experiments, protocols for the preparation of solid supported model membranes, mimicking the overall lipid composition of diatoms and containing the three glycolipids monogalactosyldiacylglycerol, digalactosyldiacylglycerol and sulfoquinovosyl-diacylglycerol were established. Artificial model membranes were successfully prepared and characterized on hydrophobically functionalized gold and glass supports as well as on hydrophilic silicon dioxide and mica surfaces. These model systems were first applied to study the interactions of two exemplary recombinant cingulins with lipid membranes. Cingulins show structural similarities to silaffins and were recently identified as part of the organic matrix inside the diatom biosilica. Adsorption measurements revealed no significant interactions between these proteins and lipid membranes. In addition, long-chain polyamines (LCPA) marked a second class of biomolecules localized in the diatom biosilica and were used in this study as well. LCPA are known to aggregate in solution and catalyze silica precipitation. Herein, for the first time, synthetic LCPA with molecular masses matching the range of LCPA isolated from diatoms were investigated with regard to their interaction with lipid membranes. Upon adsorption of LCPA the formation of membrane stacks was observed and characterized. These stacks were formed from vesicles in solution and were proven to be connected to the underlying membrane. While stack formation was found to be independent of the membrane composition, a clear dependency on polyamine chain-length was observed since only LCPA with more than five amine groups mediated stack formation.
Keywords: Long-chain polyamine; Cingulin; Plant lipid; Solid supported membrane