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BP: Fachverband Biologische Physik

BP 16: Poster Session I

BP 16.20: Poster

Dienstag, 27. März 2007, 17:00–19:30, Poster D

Particle image correlation spectroscopy (PICS) — •Stefan Semrau and Thomas Schmidt — Physics of life processes, Leiden institute of physics, Leiden university, The Netherlands

Single-particle tracking (SPT) and image correlation microscopy (ICM) have been proven to be powerful tools for the investigation of local inhomogeneities in biological systems. Driven by recent discussions on the refinement of the classical fluid-mosaic model of the plasma membrane both tools were applied to elucidate the contribution of lipid organization and protein interactions to the behavior of signaling molecules. To overcome the drawbacks of both SPT and ICM we have developed an analysis tool that combines both techniques and resolves correlations on the nanometer length and millisecond time scale (Semrau and Schmidt, Biophys. J., Vol. 92, 2007). This tool, adapted from methods of spatiotemporal image correlation spectroscopy, exploits the high positional accuracy of single-particle tracking. While conventional tracking methods break down if multiple particle trajectories intersect, our method works for arbitrarily large molecule densities and diffusion coefficients as long as individual molecules can be identified. It is computationally cheap and robust and requires no a priori knowledge about the dynamical coefficients. We demonstrate the validity of the method by Monte Carlo simulations and by application to single-molecule tracking data of membrane-anchored proteins in live cells. The results faithfully reproduce those obtained by conventional tracking: upon activation, a fraction of the small GTP-ase H-Ras is confined to domains of < 200 nm diameter.