Friday 17 Oct 2014Nanomechanics and interfaces of biological systems with dynamic AFM: from single membrane proteins to live cells.

Dr. Sonia Antoranz Contera - University of Oxford

Newman Red 12:30-13:30

From a physicists viewpoint, biological systems exploit the physical chemistry of molecules to engineer entropy, thermal fluctuations and molecular forces and create functional structures with complex mechanical properties (stiffness, elasticity, adhesion), tailored interfaces and diffusion properties. These structures enable biological function, from the selectivity of a membrane channel, to cell division and morphogenesis, and are altered by disease or trauma. We have developed techniques based on the atomic force microscope (AFM) that have enabled us to measure the interfaces of biological molecules and structures with physiological fluids: we have been able to measure the solid-liquid adhesion energy with sub-nm resolution using small-amplitude amplitude modulation AFM [1] and to quantify the complex electrostatics of membrane proteins measuring ionic effects on the water structure at the interface [2]. We have quantified the stiffness of a single membrane protein [3] and related it to its interface properties [2], dynamics [4,5], individual function [6] and the coupling with neighbouring proteins [4]. Using multifrequency AFM we have been able to quantitatively map the nanomechanical properties of living cells with unprecedented speed and accuracy [7]; this will make it possible to study the fundamental mechanisms that determine cell mechanics in different contexts and to exploit this knowledge to design biomaterials (nanostructure-based drug-delivery systems, and nanocomposites for tissue regeneration) that enable selectivity and biocompatibility by controlling adhesion, diffusion [8] and mechanical properties.

1. Voitchovsky et al. Direct mapping of the solid-liquid adhesion energy with subnanometre resolution Nature Nanotechnology 5, 401405 (2010).
2. Contera et al. Controlled ionic condensation at the surface of a native extremophile membrane. Nanoscale, 2, 222-229 (2010).
3. Voitchovsky et al. Differential stiffness and lipid mobility in the leaflets of purple membranes Biophysical Journal, 90 (6), 2075-2085 (2006)
4. Voitchovsky et al. Lateral coupling and cooperative dynamics in the function of the native membrane protein bacteriorhodopsin Soft Matter 5 (24), 4899-4904 (2009).
5. Yamashita et al. Journal of Structural Biology, 167 (2), 153-158 (2009).
6. Voitchovsky et al. Dynamics of bacteriorhodopsin 2D crystal observed by high-speed atomic force microscopy Biophysical Journal, 93 (6), 2024-2037 (2007).
7. Raman, et al. Mapping nanomechanical properties of live cells using multi-harmonic atomic force microscopy, Nature Nanotechnology 6 (2011) 809-814.
8. Axpe, et al. Sub-nanoscale free volume and local elastic modulus of chitosan/carbon nanotube nanocomposite scaffolds for tissue engineering, Submitted 2014.

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