Regensburg 2004 – scientific programme
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AKB: Biologische Physik
AKB 50: Poster Session "Biological Physics"
AKB 50.132: Poster
Friday, March 12, 2004, 10:30–13:00, B
Thermal fluctuation analysis of grafted microtubules — •Francesco Pampaloni1, Gianluca Lattanzi2, A. Jonas1, Erwin Frey2, Ernst-Ludwig Florin1, and 3 — 1EMBL, Meyerhofstrasse 1, D-69117 Heidelberg — 2Abteilung Theorie, Hahn-Meitner Institut, Glienicker Strasse 100, D-14109 Berlin — 3
Cytoskeletal filaments play a fundamental role in imparting polarity to the cell, determining the plane of symmetry in cell division, and regulating cell movements and shape. Unlike most of the synthetic organic polymers, cytoskeletal filaments are semiflexible polymers, with a typical stiffness that is intermediate between that of a random coil and that of a rigid rod. A basic parameter for characterizing the stiffness of polymeric fibres is the persistence length, which is defined as the typical length over which correlations of the tangent vectors of the filament contour decay. A persistence length comparable to the filaments contour length, defined as the maximum end-to-end distance, is a characteristic property of semiflexible polymers. Whereas an established theoretical framework already exists for flexible polymers, the static and dynamic properties of single semiflexible filaments are still the object of intense and challenging theoretical investigations [1]. Semiflexible chains have many interesting features that disappear in the flexible and stiff limits. For example, the distribution function of the end-to-end distances has a typical non-Gaussian shape with the weight of the distribution shifting toward full stretching [2, 3]. In this work, we present a novel method to measure the predicted end-to-end distributions for grafted microtubules in three-dimensions using a recently developed method for high-resolution particle tracking [4] and without any disturbance by surface effects that affects earlier work. In our assay, one end of the microtubules is grafted to a gold substrate while the other end is freely fluctuating in solution. The thermally-driven motion of the microtubules is measured by tracking the positions of single 200 nm fluorescent beads attached to them. Since the supporting substrate is placed tens of micrometers apart from the top and bottom boundaries of the measuring chambers, every influence due to surface effects is negligible. This is an improvement with respect to the alternative assays previously developed for measuring the mechanical properties of microtubules [5, 6, 7, 8] or actin [9], where surface effects could not be completely excluded. Our experimental results show a non-Gaussian distribution of longitudinal fluctuations for microtubules of length 5 micron. The measured half-width of the longitudinal and transverse fluctuations is typically about 50 nm and 400 nm, respectively. The non-Gaussian longitudinal distribution indicates that taxol-treated microtubules show the typical behaviour of semiflexible polymers also on the typical length scale of a cell.
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