Jonne Seppälä

University of Jyväskylä
Supervisor: Jari Ylänne
Funding: other
Date: 2012-01-01

Structural and interaction studies on the C-terminal domains of filamin A

The ability of cells to sense mechanical forces is crucial for cell differentiation and maintenance of tissue architecture (for review see Hoffman et al. 2011). This phenomenon is called mechanosensor signalling and it ultimately depends on force-induced changes in protein conformation. Many mechanosensory proteins are parts of cytoskeleton and cell adhesion structures (for review see Hoffman et al. 2011). For example, cell adhesion strength is regulated according to extracellular forces and these signals might in part be transmitted via actin cross-linking proteins, filamins (for review see Sutherland-Smith, 2011).

Filamins are large, ~280 kDa dimeric rod-like proteins that anchor cytoskeleton to plasma membrane and to extracellular matrix by binding to cell surface receptors and actin filaments (for review see Nakamura et al., 2011). Each monomer has an N-terminal actin binding domain, followed by 24 immunoglobulin-like domains of which the most C-terminal ones mediate the dimerization. Humans have 3 isoforms: ubiquitously expressed A and B, and muscle specific C (for review see Nakamura et al., 2011). The complete atomic structure of filamins is not known, but several structural studies on the C-terminal domains have revealed that altogether 6 domains are pair-wisely folded (Lad et al., 2007; Heikkinen et al., 2009). This domain arrangement auto-inhibits ligand binding on filamins as the binding sites are masked. This could provide a mechanism for mechanosensory signaling (Lad et al., 2007) which has recently been supported by molecular dynamics simulations (Pentikäinen and Ylänne, 2009) and in vitro experiments (Ehrlicher et al., 2011).

The aims of my thesis are to explore the mechanically and ligand induced conformational changes in filamin A and their effects on the ligand binding interactions, and to determine high resolution structures of these dynamic domains. The main methods are direct measurements of conformational changes by Förster resonance energy transfer (FRET) and determination of complex structures by x-ray crystallography.