In this paper, single complexes of individual fibronectin molecules bound to integrin proteins were studied using atomic force microscopy (AFM). It was found that the fibronectin binds to the head region of the flat lying molecule when the integrins are adsorbed onto mica. Confirmation that fibronectin is bound was via single molecule force spectroscopy and loading rate analysis. Incorporation of the integrin into a supported lipid bilayer stabilizes the integrin in terms of its orientation. The head region of the integrin was shown to remain functional allowing single fibronectin molecules to interact with the head region protruding from the lipid bilayer surface. In addition the integrins were found to selectively partition into the gel phase DPPC domains, an observation consistent with the lipid raft hypothesis. Although a supported lipid bilayer will perturb the dynamic study of transmembrane proteins, this work demonstrates that integrins stabilized in this manner are functional and available for the study of biomolecular interactions.
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