Characterization of photophysical properties and structural effects of various protoporphyrins docked to human serum albumin preliminary study for future solar energy conversion applications
Photosensitized processes as a way to prompt changes in natural as well as engineered biomolecules have received increasing interest for the manipulation of biomaterials. In this study, we present the photo-physical properties of the interaction between HSA and various photosensitizers, including free base PPIX and metal-chelated PPIX compounds (Zn(II)PPIX, Hemin, Mg(II)PPIX, Mn(III)PPIX and Sn(IV)PPIX).
A primary obstacle in the study has been the poor solubility of the porphyrins in aqueous solution. Fortunately, we’ve been able to develop an effective improved sample preparation method to eliminate or reduce this aggregation effect, which reveals the occurrence of Förster Resonance Energy Transfer (FRET) when the porphyrins (acceptor molecule) bound to the HSA (donor molecule), based on the donor molecule has an emission spectrum that substantially overlaps with the absorption spectrum of the acceptor and the fluorescence lifetime decay spectra as well. FRET analysis provides a series of donor-acceptor distance in good agreement with the results of similar complexes resolved by X-ray diffraction. These results are used to guide the computational docking simulations, indicating the most favorable docking site for each protoporphyrin respectively.
In addition, to study the photo-event induced by photosensitizers on the protein, the irradiation experiments are performed with a 405nm diode laser. Besides the absorption, fluorescence and lifetime spectroscopic data, Circular Dichroism (CD) spectra are also recorded and analyzed to establish the extent of the changes of the secondary structure of the protein upon irradiation. Overall, the study provides a significant step forward in the field of photosensitized protein engineering.