The formation of bacterial magnetosomes by magnetotactic bacteria is an intriguing example of a biomineralization process. In the alphaproteobacterium Magnetospirillum gryphiswaldense, they consist of a monocrystalline magnetite (Fe3O4) core enveloped by the magnetosome membrane, which consists of phospholipids and a set of magnetosome-specific, membrane-associated proteins [1-3]. Due to their highly regulated biosynthesis, magnetosomes exhibit unprecedented characteristics such as high crystallinity, strong magnetization, as well as uniform shapes and sizes, which make magnetosomes highly attractive for various biomedical and biotechnological applications. Both crystal morphologies and the composition of the enveloping membrane can be manipulated by genetic means, allowing a controlled functionalization of the particle surface by genetic engineering. For that purpose, a versatile and diverse genetic “toolkit” for the generation of “smart” multifunctional magnetic nanoparticles with several tailored properties is being created.
Using an optimized expression system , several of the most abundant magnetosome membrane proteins were tested as potential membrane anchors for the magnetosome display of reporter proteins.
For the generation of particles with maximized protein-to-particle ratios arrays of up to five monomers of the model enzyme glucuronidase GusA plus the additional fluorophore eGFP were genetically fused as single large hybrid proteins to highly abundant magnetosome membrane protein anchors. GusA activity followed Michaelis-Menten kinetics, and reaction rates were nearly triplicated compared to single GusA expression.
Furthermore, we explore the expression of versatile molecular connectors like streptavidin or nanobodies (functional fragments derived from full-length camelid antibodies) , as well as various organic coatings for increased stability and controlled surface reactivity. Thereby we expect the generation of tailored particles with improved biocompatibility and tuneable characteristics optimized for potential in vivo applications.
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