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Rap1 and membrane lipids cooperatively recruit talin to trigger integrin activation
Thomas Bromberger1, Liang Zhu2, Sarah Klapproth1
1Max-Planck-Institute of Biochemistry, Department of Molecular Medicine, 82152 Martinsried, Germany.
Journal of Cell Science
|October 4, 2019
Summary
Rap1 proteins cooperatively bind talin's F0 and F1 domains, synergizing with membrane PIP2 binding. This dual action is crucial for talin targeting, integrin activation, and cell adhesion.
Area of Science:
- Cell Biology
- Molecular Biology
- Biochemistry
Background:
- Integrin activation is initiated by talin recruitment and tethering to the plasma membrane.
- Rap1 proteins, RIAM, and PIP2 are known to bind talin and regulate integrin activation, but their roles require systematic analysis.
Purpose of the Study:
- To systematically analyze the roles of Rap1, RIAM, and PIP2 in talin targeting and integrin activation.
- To elucidate the cooperative binding mechanisms of Rap1 to talin.
Main Methods:
- Expression of specific talin mutants in talin-null fibroblasts.
- Nuclear Magnetic Resonance (NMR) analysis to characterize Rap1-binding sites on talin.
- Assessment of cell adhesion, spreading, talin recruitment, and integrin activation.
Main Results:
- Talin F0 domain binding to Rap1 synergizes with talin F2 domain lipid binding for membrane targeting and integrin activation.
- Talin rod interaction with RIAM is dispensable for these processes.
- A second Rap1-binding site in the talin F1 domain was identified, and its mutation, similar to the F0 mutant, inhibited cell adhesion and integrin activation.
- Mutating both Rap1-binding sites exacerbated the observed defects.
Conclusions:
- Cooperative Rap1 binding to talin F0 and F1 domains, alongside membrane PIP2 binding, spatiotemporally positions and activates talin.
- This mechanism regulates integrin activity and is critical for cell adhesion and spreading.
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