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BMBF Arbeitsgruppenwettbewerb Glykobiotechnologie
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Supramolecular Self-Organization in Biology and Biotechnology
The self-organization of molecules into dynamic and hierarchical supramolecular assemblies is a key feature in biology. The resulting architectures exhibit collective properties that are distinct from those that characterize its individual components. Our group is particularly interested in two types of assemblies: lipid membranes and the gel-like, polysaccharide-rich coats that surround many cells.
For a thorough investigation of the physical principles underlying the structure and function of these architectures, it is desirable to move from living cells with their complex dynamics to well-controlled models with tunable complexity. We create such model systems on solid supports. We employ modern techniques of surface nanostructuration and biofunctionalization to guide the assembly down to the nanometer-scale.
For the characterization of the model systems, we develop and use a toolbox of biophysical in situ characterization techniques, including quartz crystal microbalance with dissipation monitoring (QCM D), atomic force microscopy (AFM), reflection interference contrast microscopy (RICM), ellipsometry and fluorescence methods.
Our work at the MPI for Metals Research is funded by the BMBF-Arbeitsgruppenwettbewerb "Glycobiotechnology".
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The pericellular coat
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Many cells equip themselves with a gel-like coat that is rich in the polysaccharide hyaluronan. This pericellular coat can reach a thickness of several micrometers. It is invisible in common light microscopy, since its extreme hydration renders the optical contrast very low. The grafting of hyaluronan to the cell membrane and its interaction with hyaluronan-binding molecules can give rise to different supramolecular structures, such as cross-linked networks or polyelectrolyte brushes.
By reconstituting these intriguing structures in vitro, the physico-chemical properties of such coats can be quantified. We create model systems of the pericellular coat that are based on supported lipid membranes. This immobilization platform allows us to create hyaluronan layers with well-defined composition and structure, such as brushes of nd-grafted hyaluronan.
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How to re-construct a hyaluronan coat?
A silica surface was first functionalized with a supported lipid bilayer (SLB) and the protein linker streptavidin. Hyaluronan molecules were then immobilized with one of their ends. The surface functionalization and the immobilization of hyaluronan can be followed in real time by QCM-D. Pronounced changes in frequency, accompanied by small changes in dissipation, are characteristic for the SLB and the protein layer. The strong increase in dissipation upon hyaluronan binding reflects the highly hydrated and viscoelastic state of the hyaluronan-brush.
The brush can reach a thickness of up to 500 nm. Important properties of the hyaluronan film, such as its permeability, can be probed directly. The film shown here is permeable to lipid vesicles of around 30 nm in size.
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References:
R.P. Richter, K.K. Hock, J. Burkhartsmeyer, H. Boehm, P. Bingen, G. Wang, N.F. Steinmetz, D.J. Evans, and J.P. Spatz Journal American Chemical Society 2007, 127, 5306-5307.
R.P. Richter, R. Bérat, and A.R. Brisson Langmuir 2006, 22, 3497-3505.
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