Adsorption and enzymatic cleavage of osteopontin at interfaces with different surface chemistries

Abstract

Osteopontin is a highly charged glycoprotein present in the extra cellular matrix of a wide range of tissues. It is, in particular, relevant for biomaterials through its role in mineralized tissue remodeling. The adsorption and enzymatic cleavage of osteopontin at four different surface chemistries (methyl-, carboxylic-, and amine-terminated alkanethiol self-assembled monolayers and bare gold) have been studied utilizing a combination of the quartz crystal microbalance with dissipation and surface plasmon resonance. Full length bovine milk osteopontin was used which is well characterized with respect to post-translational modifications. Osteopontin adsorbed at all the surfaces formed thin (similar to 2-5 nm) hydrated layers with the highest amount of protein and the highest density layers observed at the hydrophobic surface. Less protein and a higher level of hydration was observed at the polar surfaces with the highest level of hydration being observed at the gold surface. The energy dissipation of these thin films (as measured by the Delta D/Delta F value) was altered at the different surface chemistries and interestingly a higher dissipation correlated with a higher density. Thrombin was able to bind and cleave the surface bound osteopontin at the hydrophobic surface. The altered levels of osteopontin binding, hydration of the layer, and susceptibility to thrombin cleavage suggest that osteopontin adopts different conformations and/or orientations at the different material surfaces. (C) 2009 American Vacuum Society. [DOI: 10.1116/1.3187529]