Cooperative mechanosensitivity and allostery of focal adhesion clusters

Abstract

We analyse the role of cooperative interaction between neighbouring adhesion-mechanosensor complexes by constructing an Ising-like Hamiltonian describing the free energy of cell adhesion on a substrate as a lattice of 3-state mechanosensing sites involving focal adhesion kinase (FAK). We use a Monte Carlo stochastic algorithm to find equilibrium configurations of these mechanosensors in two representative geometries: on a 1D ring representing the rim of a cell on a flat surface, and a 2D bounded surface representing the whole area of cell contact with a flat surface. The level of FAK activation depends on the pulling force applied to the individual FAK-integrin via actin-myosin contractile networks, and the details of the coupling between individual sensors in a cluster. Strong coupling is shown to make the FAK sensors experience a sharp on-off behaviour in their activation, while at low coupling the activation/autoinhibition transition occurs over a broad range of pulling force. We find that the activation/autoinhibition transition of FAK in the 2D system with strong coupling occurs with a hysteresis, the width of which depends on the rate of change of force. The effect of introducing a regulating protein (such as Src) in a limited quantity to control FAK activation is explored, and visualizations of clustering in both topologies are presented. In particular the results on the bounded 2D surface indicate that clustering of active FAK occurs preferentially at the boundary, in agreement with experimental observations of focal adhesions in cells.

Direct visualization by FRET-FLIM of a putative mechanosome complex involving Src, Pyk2 and MBD2 in living MLO-Y4 cells

“…Src and Pyk2 are tyrosine kinases that associate with the cytoplasmic domain of integrins in focal adhesions, sites of interaction between cells and the extracellular matrix (ECM) [ 13 ]. Focal adhesions have been proposed as likely sites of mechanosensation in cells, being perfectly positioned at sites of cell-ECM interaction to detect changes in fluid shear stress or substrate strain [ 14 – 17 ]. MBD2 is a methylated DNA binding protein that is localized primarily in the nucleus [ 6 , 18 , 19 ].…”