Protein-nanoparticle construct for intracellular delivery

Abstract

Proteins are essential parts of organisms and participate in virtually every process within cells. Being able to control them, deliver them to specific locations or give them desired functionalities and properties pave the way to numerous applications, including use as biosensors, within biocatalysis and biomedical devices. Thus, protein monitoring is extremely relevant and one of the most important challenges in biotechnology. One way to protein monitoring could be related to understanding and controlling their tertiary structure. It is known that the properties and functions of proteins are determined by their conformation. Therefore being able to induce conformational changes in proteins may be a possible way to control them. In the present study, a series of experiments with Bovine serum albumin (BSA) were performed, analyzed and described to understand the adsorption, unfolding behaviour and conformational changes in tertiary structure of this protein when it was attached and spread on the surface of different types of polymer nanoparticles. BSA was selected since it is wellstudied protein, the most abundant protein in plasma and one of the most used model protein. Three kinds of negatively charged monodisperse polymer nanoparticles were elaborated by soap free emulsion polymerization: two different size polymer nanoparticles with epoxy groups and one type of polymer nanoparticles without epoxy groups. Finally, size and zeta potential measurements of corresponding BSA-polymer nanoparticle constructs, fluorescence spectroscopy, isothermal titration calorimetry (ITC) and unfolding studies with urea were carried out to study BSA conformational isomerisation in immobilized polymer nanoparticle systems. All experiments were done at three different pH conditions; 3.8, 7.4 and 9, corresponding to conditions below and above the isoelectric point (pI) of BSA. BSA immobilization and degree of unfolding was found to be strongly affected by pH and matching of the global protein and polymer nanoparticle charges. The results suggested that polymer nanoparticles with epoxy groups offered covalent binding with stronger attachment and larger conformational isomerisation than polymer nanoparticles without epoxy groups. These changes occurred to the largest degree at pH 7.4. This may be due to a high number of epoxy groups conjugated with amino groups of the protein. At pH 3.8 it seemed that the attachment of BSA was highest but without relevant structural alterations while at pH 9 it was in an intermediate level of adsorption and structural changes. Finally, there were no appreciable discrepancies between different size polymer nanoparticles.