Structural and Biochemical Basis for the Inhibitory Effect of Liprin-α3 on Mouse Diaphanous 1 (mDia1) Function

• Published in: The Journal of biological chemistry 2015-06, Vol.290 (23), p.14314-14327
• Main Authors: Brenig, Julian, de Boor, Susanne, Knyphausen, Philipp, Kuhlmann, Nora, Wroblowski, Sarah, Baldus, Linda, Scislowski, Lukas, Artz, Oliver, Trauschies, Philip, Baumann, Ulrich, Neundorf, Ines, Lammers, Michael
• Format: Article
• Language: English
• Subjects: actin; Actins - metabolism; Amino Acid Sequence; Animals; Binding Sites; Carrier Proteins - chemistry; Carrier Proteins - metabolism; Crystallography, X-Ray; cytoskeleton; formin; Formins; HeLa Cells; Humans; liprin; mDia1; Mice; Models, Molecular; Molecular Sequence Data; Protein Structure, Secondary; Ras homolog gene family, member A (RhoA); rhoA GTP-Binding Protein - metabolism; Signal Transduction; Vesicular Transport Proteins - chemistry; Vesicular Transport Proteins - metabolism
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1074/jbc.M114.621946

Diaphanous-related formins are eukaryotic actin nucleation factors regulated by an autoinhibitory interaction between the N-terminal RhoGTPase-binding domain (mDiaN) and the C-terminal Diaphanous-autoregulatory domain (DAD). Although the activation of formins by Rho proteins is well characterized, its inactivation is only marginally understood. Recently, liprin-α3 was shown to interact with mDia1. Overexpression of liprin-α3 resulted in a reduction of the cellular actin filament content. The molecular mechanisms of how liprin-α3 exerts this effect and counteracts mDia1 activation by RhoA are unknown. Here, we functionally and structurally define a minimal liprin-α3 core region, sufficient to recapitulate the liprin-α3 determined mDia1-respective cellular functions. We show that liprin-α3 alters the interaction kinetics and thermodynamics of mDiaN with RhoA·GTP and DAD. RhoA displaces liprin-α3 allosterically, whereas DAD competes with liprin-α3 for a highly overlapping binding site on mDiaN. Liprin-α3 regulates actin polymerization by lowering the regulatory potency of RhoA and DAD on mDiaN. We present a model of a mechanistically unexplored and new aspect of mDiaN regulation by liprin-α3. Background: RhoA·GTP activates mDia1 resolving an autoinhibited state leading to formation of unbranched actin filaments in cells. Results: Liprin-α3 uses an α-helical region to bind to mDia1, counteracting mDia1 activation by RhoA. Conclusion: Liprin-α3 competes with RhoA and mDia1 autoinhibition to modulate its activity. Significance: Knowing how mDia1 is inactivated is essential to understand its biology and for therapeutic approaches.