부산대학교 도서관

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1006/jmbi.1994.0070 Byline: Michael Lorenz, Katrina J.V. Poole, David Popp, Gerd Rosenbaum, Kenneth C. Holmes Keywords: actin-tropomyosin binding; X-ray fiber diffraction; electrostatic interaction; radial and azimuthal position of tropomyosin; acto-myosin binding Abstract: We present a model of the actin-tropomyosin complex in which the radial and azimuthal position of tropomyosin was adjusted to fit the X-ray fiber diffraction patterns from oriented actin-tropomysin gels at a resolution of 1/8 A.sup.-1. We used the recently published atomic F-actin model for the calculations. The atomic model of tropolyosin was obtained by model-building a coiled coiled-coil structure from the tropomyosin sequence. The resulting atomic model is strongly preferred and shows strong electrostatic interactions between charged side-chains of tropomyosin residues and actin residues in subdomain 3 and subdomain 4. Furthermore, calculations of enthalpies based upon electrostatic interactions indicate that there is a favored rotational position of the tropomyosin core at the calculated azimuthal and radial position given by the X-ray refinement. Rotations of the tropomyosin strand out of this position turn strongly attractive electrostatic interactions into repulsive forces. The resulting binding radius of 39 A and the determined azimuthal position of tropomyosin are in good agreement with electron microscopy reconstructions and neutron diffraction experiments. Furthermore, the calculated position of tropomyosin would still partly block the rigor interaction of myosin cross-bridges with actin, whereas it very likely allows undisturbed binding of the cross-bridges in a weak binding state. Article History: Received 8 September 1994; Accepted 3 November 1994