Novel structures for alpha-actinin:F-actin interactions and their implications for actin-membrane attachment and tension sensing in the cytoskeleton.
We have applied correspondence analysis to electron micrographs of 2-D rafts of F-actin cross-linked with alpha-actinin on a lipid monolayer to investigate alpha-actinin:F-actin binding and cross-linking. More than 8000 actin crossover repeats, each with one to five alpha-actinin molecules bound, were selected, aligned, and grouped to produce class averages of alpha-actinin cross-links with approximately 9-fold improvement in the stochastic signal-to-noise ratio. Measurements and comparative molecular models show variation in the distance separating actin-binding domains and the angle of the alpha-actinin cross-links. Rafts of F-actin and alpha-actinin formed predominantly polar 2-D arrays of actin filaments, with occasional insertion of filaments of opposite polarity. Unique to this study are the numbers of alpha-actinin molecules bound to successive crossovers on the same actin filament. These "monofilament"-bound alpha-actinin molecules may reflect a new mode of interaction for alpha-actinin, particularly in protein-dense actin-membrane attachments in focal adhesions. These results suggest that alpha-actinin is not simply a rigid spacer between actin filaments, but rather a flexible cross-linking, scaffolding, and anchoring protein. We suggest these properties of alpha-actinin may contribute to tension sensing in actin bundles.
Hampton
Cheri M
CM
Institute of Molecular Biophysics, The Florida State University, Tallahassee, FL 32306-4380, USA.
Taylor
Dianne W
DW
Taylor
Kenneth A
KA
D008841:Actin Cytoskeleton / Q000737:chemistry / Q000378:metabolism; D000185:Actinin / Q000737:chemistry* / Q000378:metabolism*; D000199:Actins / Q000737:chemistry* / Q000378:metabolism*; D000818:Animals; D002462:Cell Membrane / Q000378:metabolism*; D003599:Cytoskeleton / Q000378:metabolism*; D008958:Models, Molecular; D011485:Protein Binding; D025941:Protein Interaction Mapping; D011817:Rabbits; D013500:Surface Tension
D000199:Actins; D000185:Actinin