Adhesion of α₅β₁ receptors to biomimetic substrates constructed from peptide amphiphiles

Biomimetic membrane surfaces functionalized with fragments of the extracellular matrix protein, fibronectin, are constructed from mixtures of peptide and polyethylene glycol (PEG) amphiphiles. Peptides from the primary binding loop, GRGDSP, were used in conjunction with the synergy site peptide, PHSRN, in the III_9-10 sites of human fibronectin. These peptides were attached to dialkyl lipid tails to form peptide amphiphiles. PEG amphiphiles were mixed in the layer to minimize non-specific adhesion in the background. GRGDSP and PEG amphiphiles or GRGDSP, PHSRN, and PEG amphiphiles were mixed in various ratios and deposited on solid substrates from the air-water interface using Langmuir-Blodgett techniques. In this method, peptide composition, density, and presentation could be controlled accurately. The effectiveness of these substrates to mimic native fibronectin is evaluated by their ability to generate adhesive forces when they are in contact with purified activated α₅β₁ integrin receptors that are immobilized on an opposing surface. Adhesion is measured using a contact mechanical approach (JKR experiment). The effects of membrane composition, density, temperature, and peptide conformation on adhesion to activated integrins in this simulated cell adhesion setup were determined. Addition of the synergy site, PHSRN, was found to increase adhesion of α₅β₁ to biomimetic substrates markedly. Increased peptide mobility (due to increased experimental temperature) increased integrin adhesion markedly at low peptide concentrations. A balance between peptide density and steric accessibility of the receptor binding face to α₅β₁ integrin was required for highest adhesion.