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© The Rockefeller University Press, 0021-9525/1997//387 $5.00
The Journal of Cell Biology, Volume 139, Number 2, , 1997 387-396

Article

Evidence for a Conformational Change in Actin Induced by Fimbrin (N375) Binding



Dorit Hanein*, Paul Matsudaira{ddagger}, and David J. DeRosier*

* The W.M. Keck Institute for Cellular Visualization and The Rosenstiel Basic Medical Sciences Research Center, Department of Biology, Brandeis University, Waltham, Massachusetts 02254; and {ddagger} Whitehead Institute of Biomedical Research and Department of Biology, Massachusetts Institute of Technology, Cambridge, Massachusetts 02142

Fimbrin belongs to a superfamily of actin cross-linking proteins that share a conserved 27-kD actin-binding domain. This domain contains a tandem duplication of a sequence that is homologous to calponin. Calponin homology (CH) domains not only cross-link actin filaments into bundles and networks, but they also bind intermediate filaments and some signal transduction proteins to the actin cytoskeleton. This fundamental role of CH domains as a widely used actin-binding domain underlines the necessity to understand their structural interaction with actin. Using electron cryomicroscopy, we have determined the three-dimensional structure of F-actin and F-actin decorated with the NH2-terminal CH domains of fimbrin (N375). In a difference map between actin filaments and N375-decorated actin, one end of N375 is bound to a concave surface formed between actin subdomains 1 and 2 on two neighboring actin monomers. In addition, a fit of the atomic model for the actin filament to the maps reveals the actin residues that line, the binding surface. The binding of N375 changes actin, which we interpret as a movement of subdomain 1 away from the bound N375. This change in actin structure may affect its affinity for other actin-binding proteins and may be part of the regulation of the cytoskeleton itself. Difference maps between actin and actin decorated with other proteins provides a way to look for novel structural changes in actin.

Abbreviations used in this paper: ABD, actin-binding domain; Actin-N375, {alpha}-rabbit skeletal muscle actin filaments decorated with the NH2-terminal ABD of human T-fimbrin; CH, calponin homology; 3D, three dimensional; F-actin, {alpha}-rabbit skeletal muscle actin filaments; N375, NH2-terminal ABD of human T-fimbrin (1–375 amino acids).

Address all correspondence to Dr. Dorit Hanein, W.M. Keck/Rosenstiel Center, Brandeis University, 415 South St. (MS-029), Waltham, Massachusetts 02254-9110. Tel.: (781) 736-2467. Fax: (781) 736-2419.

This paper is dedicated to the memory of Mary S. Tilney.


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