With the completion of the Human Genome Project and the emerging proteomics era, the biosciences community is beginning the daunting task of understanding the structures and the structure-function relations of collections of interacting proteins. Cellular activity, which is tightly regulated, often results from protein-protein and protein-nucleic acid interactions, leading to the formation of large assemblies of biomolecules for distinct functions. Examples include DNA condensation during the cell cycle, and bundle and network formation of filamentous actin proteins in cell attachment, motility, and cytokinesis.

A group of researchers from the University of California at Santa Barbara have recently reported on the structure of filamentous (F) actin complexed with the actin cross-linking protein a-actinin. The synchrotron-based SSRL work has led to a proposed structure of F-actin bundles showing how the cross-linking protein a-actinin induces a network-like structure in F-actin at low concentrations, with a gradual transition as a function of increasing concentration, to a bundle phase consisting of a disordered nanoscale quasi-square lattice. The work, carried out by O. Pelletier, E. Pokidysheva, L. S. Hirst, N. Bouxsein, Y. Li and C. R. Safinya, appeared in Physical Review Letters (volume 91, number 14, 148102, 2003), and was further highlighted as the Cover Image of the October 3rd issue. The research was supported by the National Institutes of Health, the National Science Foundation, and the Department of Energy.

To learn more about this research see the full scientific highlight at:
http://www-ssrl.slac.stanford.edu/research/highlights_archive/actinin.html