Protein secondary structure and solvent accessibility of proteins in decellularized heart valve scaffolds

Abstract

Decellularized heart valve scaffolds can be used for pulmonary heart valve replacements in heart surgery. In order to assess quality parameters of heart valves prior to implantation into patients various techniques can be applied, including ultrastructural evaluation and biomechanical testing. Fourier transform infrared spectroscopy (FTIR) was used here to study protein secondary structure and solvent accessibility in decellularized heart valve matrices. FTIR was used to study proteins in the three main types of structures in decellularized heart valves: leaflet, pulmonary artery wall and heart muscle. The amide-I band region was used to reveal differences in the overall protein secondary structure amongst tissues. Leaflet material contains a relatively high contribution of α-helical structures, whereas artery matrix contains a relatively high content of triple-helix and β-sheet structures. Solvent accessibility of tissue proteins was studied by exposing material to D₂O. The exchange of hydrogen of the NH amide-II bond for deuterium originating from D₂O was visible as an increase in the area of the amide-II band (1500–1400 cm⁻¹). The amide-I band also depicted changes in shape and position during incubation in D₂O: a low frequency band at around 1625 cm⁻¹ increased as a function of time. Remarkable differences in hydrogen-to-deuterium exchange kinetics and protein solvent accessibility were observed among the three types of heart valve matrices: proteins in artery matrix are highly accessible to solvent, whereas proteins in leaflet and heart muscle structures are relatively inaccessible to solvent and show slow hydrogen/deuterium exchange. The differences in protein solvent accessibility in the different types of matrices likely reflect differences in scaffold porosity.