Sitar, T., Gallinger, J., Ducka, A.M., Ikonen, T.P., Wohlhoefler, M., Schmoller, K.M., Bausch, A.R., Joel, P., Trybus, K.M., Noegel, A.A., Schleicher, M., Huber, R., Holak, T.A. (2011). Molecular architecture of the Spire-actin nucleus and its implication for actin filament assembly.  Proc. Natl. Acad. Sci. U.S.A. 108(49): 19575--19580.

FBrf0218145

Research paper

The Spire protein is a multifunctional regulator of actin assembly. We studied the structures and properties of Spire-actin complexes by X-ray scattering, X-ray crystallography, total internal reflection fluorescence microscopy, and actin polymerization assays. We show that Spire-actin complexes in solution assume a unique, longitudinal-like shape, in which Wiskott-Aldrich syndrome protein homology 2 domains (WH2), in an extended configuration, line up actins along the long axis of the core of the Spire-actin particle. In the complex, the kinase noncatalytic C-lobe domain is positioned at the side of the first N-terminal Spire-actin module. In addition, we find that preformed, isolated Spire-actin complexes are very efficient nucleators of polymerization and afterward dissociate from the growing filament. However, under certain conditions, all Spire constructs--even a single WH2 repeat--sequester actin and disrupt existing filaments. This molecular and structural mechanism of actin polymerization by Spire should apply to other actin-binding proteins that contain WH2 domains in tandem.

PMC3241762 (PMC) (EuropePMC)