Molecular switches in the cell: fibronectin as a mechanical switch (vogel, 2002) Fibronectin is an adhesion protein secreted by cells and assembled into fibrils to support adhesion and migration Composed of" of fibronectin repeats Fnl, Fnll, and Fnlll connected by short linkers of varying flexibility One particular Fnlll repeat, Fnlll10, contains the RGD amino acid sequence Fnlll modules have interesting force-responsive properties o undergo partial unfolding in response to physiological forces(Figure shows stretched FN repeats in fibrillar FN) integrins bind to and pull on FN fibers through the cytoskeleton o Several potential roles for this sensitivity Expose buried recognition sites So-called sites in Fnllll, Fnlll7-8, Fnlll1o, and FnIlll4 Change relative distance between synergistic binding sites on 2 different modules E. g RGD synergy site between Fnlllg and Fnlll1o Mechanical deformation and straightening of recognition sites onMolecular switches in the cell: fibronectin as a mechanical switch (Vogel, 2002) ƒ Fibronectin is an adhesion protein secreted by cells and assembled into fibrils to support adhesion and migration ƒ Composed of ‘modules’ of fibronectin repeats FnI, FnII, and FnIII connected by short linkers of varying flexibility ƒ One particular FnIII repeat, FnIII10, contains the RGD amino acid sequence ƒ FnIII modules have interesting force-responsive properties o undergo partial unfolding in response to physiological forces (Figure shows stretched FN repeats in fibrillar FN) ƒ integrins bind to and pull on FN fibers through the cytoskeleton o Several potential roles for this sensitivity: ƒ Expose buried recognition sites x So-called ‘cryptic’ sites in FnIII1, FnIII7-8, FnIII10, and FnIIII14 ƒ Change relative distance between synergistic binding sites on 2 different modules x E.g. RGD synergy site between FnIII9 and FnIII10 ƒ Mechanical deformation and straightening of recognition sites on loops