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Membrane targeting of the spir·formin actin nucleator complex requires a sequential handshake of polar interactions.

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Tittel,  Janine
Schwille, Petra / Cellular and Molecular Biophysics, Max Planck Institute of Biochemistry, Max Planck Society;

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Schwille,  Petra
Schwille, Petra / Cellular and Molecular Biophysics, Max Planck Institute of Biochemistry, Max Planck Society;

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Weidemann,  Thomas
Schwille, Petra / Cellular and Molecular Biophysics, Max Planck Institute of Biochemistry, Max Planck Society;

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Zitation

Tittel, J., Welz, T., Czogalla, A., Dietrich, S., Samol-Wolf, A., Schulte, M., et al. (2015). Membrane targeting of the spir·formin actin nucleator complex requires a sequential handshake of polar interactions. The Journal of biological chemistry, 290(10), 6428-6444. doi:10.1074/jbc.M114.602672.


Zitierlink: http://hdl.handle.net/11858/00-001M-0000-0026-A372-5
Zusammenfassung
Spir and formin (FMN)-type actin nucleators initiate actin polymerization at vesicular membranes necessary for long range vesicular transport processes. Here we studied in detail the membrane binding properties and protein/protein interactions that govern the assembly of the membrane-associated Spir·FMN complex. Using biomimetic membrane models we show that binding of the C-terminal Spir-2 FYVE-type zinc finger involves both the presence of negatively charged lipids and hydrophobic contributions from the turret loop that intrudes the lipid bilayer. In solution, we uncovered a yet unknown intramolecular interaction between the Spir-2 FYVE-type domain and the N-terminal kinase non-catalytic C-lobe domain (KIND) that could not be detected in the membrane-bound state. Interestingly, we found that the intramolecular Spir-2 FYVE/KIND and the trans-regulatory Fmn-2-FSI/Spir-2-KIND interactions are competitive. We therefore characterized co-expressed Spir-2 and Fmn-2 fluorescent protein fusions in living cells by fluorescence cross-correlation spectroscopy. The data corroborate a model according to which Spir-2 exists in two different states, a cytosolic monomeric conformation and a membrane-bound state in which the KIND domain is released and accessible for subsequent Fmn-2 recruitment. This sequence of interactions mechanistically couples membrane binding of Spir to the recruitment of FMN, a pivotal step for initiating actin nucleation at vesicular membranes.