Magnetite-OmpA Nanobioconjugates as Cell-Penetrating Vehicles with Endosomal Escape Abilities

Outer membrane protein A (OmpA) has been extensively studied in Gram-negative bacteria due to its relevance in the adhesion of pathogens to host cells and its surfactant capabilities. It consists of a hydrophobic β-barrel domain and a hydrophilic periplasmic domain, that confers OmpA an amphiphilic structure. This study aims to elucidate the capacity of Escherichia coli OmpA to translocate liposomal membranes and serve as a potential cell-penetrating vehicle. We immobilized OmpA on magnetite nanoparticles and investigated the possible functional changes exhibited by OmpA after immobilization. Liposomal intake was addressed using egg lecithin liposomes as a model, where magnetite-OmpA nanobioconjugates were able to translocate the liposomal membrane and caused a disruptive effect when subjected to a magnetic field. Nanobioconjugates showed both low cytotoxicity and hemolytic tendency. Additional interactions within the intracellular space led to altered viability results via 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT). Confocal microscopy images revealed that immobilized nanoparticles effectively enter the cytoplasm of THP-1 and Vero cells by different routes, and, subsequently, some escape endosomes, lysosomes, and other intracellular compartments with relatively high efficiencies. This was demonstrated by co-localization analyses with LysoTracker green that showed Pearson correlations of about 80 and 28%.