Structure of Actin Cross-Linked with -Actinin: A Network of Bundles

148102-1 Three-dimensional laser scanning confocal microscopy has revealed that filamentous actin, when complexed with the cross-linking protein -actinin, will spontaneously assemble on a micron scale into a structure comprised of a relatively rigid, frequently branching, 3D network of bundles with characteristic mesh size of the order of the persistence length of F-actin. In contrast, additional nanoscale ordering is observed, as synchrotron x-ray diffraction has revealed a disordered, distorted square lattice of actin fibers within the individual bundles.