Nanoscale architecture of integrin-based cell adhesions

Abstract

The physical linkage between the extracellular matrix and the actin cytoskeleton of a cell is made by structures known as focal adhesions, acting through integrin receptors. They are of fundamental importance in human physiology because they mediate cell adhesion, mechanosensing and signalling for the control of cell growth and differentiation. The molecular architecture of focal adhesions has now been determined using three-dimensional super-resolution fluorescence microscopy to map protein organization at the nanoscale level. They are revealed as well-organized ultrastructures in which integrins and actin are separated by a 40-nanometre-long core consisting of partially overlapping protein-specific layers, spanned by talin tethers. The multilaminar architecture creates three or more separate compartments that mediate the interdependent functions of focal adhesions. Focal adhesions link the extracellular matrix by integrin receptors to cytoplasmic actin filaments and are fundamental to human physiology. These authors determine the molecular architecture of focal adhesions by mapping protein organization at the nanoscale level. The results demonstrate that focal adhesions possess a well-organized ultrastructure made up of at least three spatial and functional compartments that mediate their interdependent functions. Cell adhesions to the extracellular matrix (ECM) are necessary for morphogenesis, immunity and wound healing1,2. Focal adhesions are multifunctional organelles that mediate cell–ECM adhesion, force transmission, cytoskeletal regulation and signalling1,2,3. Focal adhesions consist of a complex network4 of trans-plasma-membrane integrins and cytoplasmic proteins that form a <200-nm plaque5,6 linking the ECM to the actin cytoskeleton. The complexity of focal adhesion composition and dynamics implicate an intricate molecular machine7,8. However, focal adhesion molecular architecture remains unknown. Here we used three-dimensional super-resolution fluorescence microscopy (interferometric photoactivated localization microscopy)9 to map nanoscale protein organization in focal adhesions. Our results reveal that integrins and actin are vertically separated by a ∼40-nm focal adhesion core region consisting of multiple protein-specific strata: a membrane-apposed integrin signalling layer containing integrin cytoplasmic tails, focal adhesion kinase and paxillin; an intermediate force-transduction layer containing talin and vinculin; and an uppermost actin-regulatory layer containing zyxin, vasodilator-stimulated phosphoprotein and α-actinin. By localizing amino- and carboxy-terminally tagged talins, we reveal talin’s polarized orientation, indicative of a role in organizing the focal adhesion strata. The composite multilaminar protein architecture provides a molecular blueprint for understanding focal adhesion functions.