Berlin 2015 – scientific programme

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BP: Fachverband Biologische Physik

BP 35: Membranes and vesicles II (joint BP/CPP)

BP 35.10: Talk

Wednesday, March 18, 2015, 17:45–18:00, H 1028

Addressing Multivalent Interactions Using Single Particle Tracking — •Stephan Block, Srdjan Acimovic, Mikael Käll, and Fredrik Höök — Department of Applied Physics, Chalmers University of Technology, Gothenburg, Sweden

Multivalent interactions are observed in a multitude of biological processes (e.g., association of viruses or bacteria to their host cells). The involved receptors are nano-sized objects, making it challenging to assess the exact number of attachment points under physiological conditions. Using TIRF microscopy of fluorescently labelled, small unilamellar vesicles, which serve as a model system for the interaction of viruses with cell membranes, we show that multivalent interactions can be assessed by single particles tracking (SPT). The vesicles are linked to a supported lipid bilayer (SLB) using DNA-tethers carrying cholesterol groups at their ends, which automatically insert into the membranes and which allow a 2D diffusion of the vesicle above the SLB. The number of attachment points can be manipulated by the concentration ratio of vesicles to DNA-tethers. SPT allows to extract the diffusion coefficients on the level of single vesicles and histograms of the observed diffusion coefficients exhibit a spectrum of distinct peaks, which are related to subpopulations of vesicles differing by their number of DNA-tethers. This enables to recalculate fluctuations of the diffusion constant of a certain vesicle into fluctuations of the number of attachment points linking the vesicle to the SLB. The extension of this analysis to virus particle tracking including a comparison between SPT with fluorescence correlation spectroscopy will be discussed.