Revealing the selective interactions of fibronectin with lipid bilayers

Abstract

The interaction of extracellular matrix proteins with lipid bilayers is fundamental to cell adhesion and related processes such as tissue formation. In this paper we use atomic force microscopy to examine the interaction between fibronectin and supported lipid bilayers. For binary lipid mixtures that display phase separation, atomic force microscopy shows that fibronectin preferentially and almost exclusively interacts with the gel phase domains, sitting on top of these raised regions. Single molecule force spectroscopy confirms the location of fibronectin on the bilayer and reveals that the mechanical properties of fibronectin are affected by aggregation of the protein on the lipid. We demonstrate that it is possible to measure the thickness of the protein aggregates by identifying a protein layer breakthrough event. Of particular interest are force–distance curves that exhibit a combination of three features, a protein layer breakthrough event, a lipid bilayer breakthrough event, and a sawtooth pattern attributed to fibronectin unfolding. The combination of lipid- and protein-related events on a single force–distance profile, characterizes in detail the lipid/protein interaction. Preferential interactions of fibronectin with lipids suggest that non-specific binding could be important in extracellular matrix protein-cell interactions and that the lateral organization of the cell membrane may play an even greater role in cell adhesion than previously thought.