Studies of the structure and function of Mms6, a bacterial protein that promotes the formation of magnetic nanoparticles
Many highly ordered mineralized structures are created by living organisms that are often hierarchical in structure with fundamental structural elements at nanometer scales. The ability to fabricate such fundamental structures independently of these organisms could open many new and exciting opportunities in nanotechnology. In those cases for which there is some understanding of the biological mechanisms involved in biomineralization, proteins have been found responsible for forming the mineral structures. But, the mechanisms by which mineralization proteins function are poorly understood. Here we discuss our studies of the magnetotactic bacterial protein, Mms6, which promotes the formation in vitro of highly paramagnetic nanocrystals. Mms6 has two phases of iron binding, the first is very high affinity and the second is low affinity and cooperative with respect to iron. Our results provide evidence for a model for the mechanism of action of Mms6 in which a conformational change driven by a high affinity iron binding site in the C-terminal domain initiates a coordinated structural change involving multiple proteins to form a surface that can initiate the packing of iron into a crystal lattice. The small starting crystals might then fuse to produce larger nanoparticles as the protein islands move in a fluid hydrophobic environment of a membrane or micelles.