Novel Structures for α-Actinin:F-Actin Interactions and their Implications for Actin–Membrane Attachment and Tension Sensing in the Cytoskeleton

Abstract

We have applied correspondence analysis to electron micrographs of 2-D rafts of F-actin cross-linked with α-actinin on a lipid monolayer to investigate α-actinin: F-actin binding and cross-linking. More than 8,000 actin crossover repeats, each with 1-5 α-actinins bound, were selected, aligned, and grouped to produce class averages of α-actinin cross-links with ~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 α-actinin cross-links. Rafts of F-actin and α-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 α-actinin molecules bound to successive crossovers on the same actin filament. These "monofilament"-bound α-actinins may reflect a new mode of interaction for α-actinin, particularly in protein dense actin-membrane attachments in focal adhesions. These results suggest that α-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 α-actinin may contribute to tension sensing in actin bundles.

Investigation of Cell-Matrix Interactions Using a FRET Technique

“…The decrease in the growth rate with an increase in RGD island spacing is shown in Table 2 and this could be explained by the lack of focal adhesion formation on ligand-organized hydrogels and the decrease of cell's contractility with the substrates. 18 We found that the distance between RGD islands is essential for the formation of integrin-mediated adhesion, and this finding was consistent with the changes in the growth rate and adhesion of cells adhered on ligand-organized gels. Closely spaced ligands promote Rho-family GTPases that induce cell spreading and motility, while wider spaced ligands support cell differentiation.…”

Arg Kinase-binding Protein 2 (ArgBP2) Interaction with α-Actinin and Actin Stress Fibers Inhibits Cell Migration

“…ArgBP2␣ is localized to muscle Z-discs along with ␣-actinin, and other signaling proteins (42,43). ␣-Actinin has a mechanosensing function (44) and in dilated cardiomyopathy, a condition associated with faulty mechanosensing, ArgBP2 levels are elevated (45). ArgBP2 interactions with palladin (13) and spectrin (12) at this site are likely to further stabilize the various protein interactions.…”

Human Muscle LIM Protein Dimerizes along the Actin Cytoskeleton and Cross-Links Actin Filaments

“…This lack of calcium responsiveness is consistent with their (putative) role of AF stabilizers/cross-linkers during muscle activity. Second, contrary to selective AF cross-linkers, like fascin, which promote the formation of unipolar bundles (40,(59)(60)(61), both MLP and ␣-actinin (60,62,63) are able to generate mixedpolarity bundles. It is therefore conceivable that they cooperate at the Z disk to cross-link antiparallel AFs coming from adjoining sarcomeres.…”