Paper BI-WeA7
Study of Adsorption and Orientation of FnIII_7-10 Fibronectin Fragment on Self-Assembled Monolayers using Time of Flight Secondary Ion Mass Spectrometry

Wednesday, October 20, 2010, 4:00 pm, Room Taos

Protein adsorption and orientation plays a critical role in many biomedical applications. Fibronectin (FN) is an extracellular matrix protein that is involved in many cell processes such as adhesion, migration and growth. The orientation and conformation of FN adsorbed onto surfaces can therefore play a critical role on cell-surface interactions. In this study, the adsorbed orientation and conformation of the 7-10 fragment of FNIII was studied on three different model surfaces (self-assembled monolayers (SAMs) of C₁₁ alkanethiols on Au with -CH₃, -NH₂, and -COOH functional groups). X-ray photoelectron spectroscopy (XPS) was used to quantify the amount of protein adsorbed on the different surfaces and time-of-flight secondary ion mass spectrometry (ToF-SIMS) was used to characterize their orientation and conformation. A trehalose coating was also used to inhibit the conformation changes due to the dehydration of the sample. With the help of principal component analysis (PCA), the peaks which are responsible for the variance observed between the spectra relative to the protein adsorbed on the different surfaces could be identified. Because the surface sensitivity of the ToF-SIMS technique is lower than average protein size, these changes in the spectra reflect differences in the conformation and the orientation of the FN fragment. Comparison of trehalose protected and unprotected samples show a significant difference in the ratio between hydrophilic and hydrophobic amino acids. The results suggest that the more hydrophilic amino acids stay on the outside of the trehalose protected protein while the more hydrophobic ones get exposed to the protein air interface upon drying. Comparison of the trehalose protected fragment on -CH₃ and ‑COOH terminated SAMs show more intense signals of Arg and Asp on the -COOH surface and more intense Val, Pro and Leu signals on the -CH₃ SAMs. The detection of these different amino acids for the protein on the different SAMs suggests that the fragment might partly denature upon adsorption to the hydrophobic surface.