Characterization of Protein Surface Interactions : Collagen and Osteocalcin
Year: 2013
Type: dissertation
Abstract: This work investigates how the proteins collagen type I and human osteocalcin interact with various surfaces. A pH-series of collagen adsorbed onto methyl terminated self-assembled monolayers has been made and the results indicate that less tropocollagen is found on the surfaces at pH below 6.0 and that biofilms made of larger fibrils with a more ordered 3D-structure are formed at pH 6.0 and above. This work also shows that it is possible to divide the amide I region of a vibrational Sum Frequency Generation (v-SFG) spectra into three peaks. These peaks can be correlated to the three amino acid residues glycine, proline and hydroxyproline, which have a high abundance in collagen. Analysis of different polarization combinations probing chiral and achiral contributions demonstrates that glycine has a higher contribution over proline and hydroxyproline in achiral responses, whereas hydroxyproline has similar or higher contribution than glycine in chiral responses, in which little to no signals from proline are detectable. v-SFG data for carboxylated and uncarboxylated osteocalcin respectively reveal that carboxylated osteocalcin has α-helices in the structure when Ca2+ ions are present in the solution, while the uncarboxylated version does not. Orientations for osteocalcin adsorbed onto hydrophobic, positively charged and negatively charged surfaces were determined by dividing peak areas of fragments from leucine, cysteine and carboxyglutamic acids from the positive Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS) spectra. Also, it was exercised to find the v-SFG signal with a femtosecond SFG system by utilizing the non-resonant background of a gold substrate and then delay the visible laser beam to only get signals from the vibrating molecules. Self-assembled monolayers (SAMs) prepared from dodecanethiols were used to demonstrate this principle, but the approach is valid also for other molecular systems.
Author: Patrik K. Johansson
Language: English
Subfield: Surfaces, Coatings and Films
Field: Materials Science
Domain: Physical Sciences
Open Access status: green
OpenAlex ID: W163667967