Magnetotactic bacteria mineralize magnetite nanoparticles inside vesicles that are aligned along a protein filament. Bacterial magnetite nanoparticles are single crystals in the size range of magnetic single domains and exhibit a strain-specific shape. Together these properties are responsible for the outstanding magnetic properties of these biogenic magnetite crystals. Mineralization of these magnetite crystals is genetically controlled but the function of many molecular players still remains unknown.
Here, we are investigating proteins that are putatively involved in the formation of these magnetite crystals, particularly, in the control of their shape. Hence, we recombinantly express these proteins and purify them to identify their binding capacity to magnetite in a first step. We report the establishment of a pull-down binding assay, which offers the possibility to test protein-mineral interactions under different conditions. For this assay, the proteins of interest are equipped with a fluorescent tag. This provides a straight forward detection method that allows for quantifying their interaction with synthetic magnetite nanoparticles produced by co-precipitation. Next, we perform single molecule force spectroscopy and quantify the binding strength between selected proteins and magnetite surfaces. Proteins that show strong and specific binding are subsequently used as additives in magnetite nanoparticle synthesis to test their role in mineralization.
The results extend our knowledge about biomineralizing macromolecules and will help to develop green synthetic routes and for utilizing magnetite particles for applications in bio- and nanotechnologies.