Immobilized biomineralizing protein Mms6 templates the formation of uniform magnetite nanoparticles in situ when selectively patterned onto a surface. Magnetic force microscopy shows that the stable magnetite particles maintain their magnetic orientation at room temperature, and may be exchange coupled. This precision-mixed biomimetic/soft-lithography methodology offers great potential for the future of nanodevice fabrication.

No abstract

Magnetotactic bacteria synthesize highly uniform intracellular magnetite nanoparticles through the action of several key biomineralization proteins. These proteins are present in a unique lipidbound organelle (the magnetosome) that functions as a nanosized reactor in which the particle is formed. A master regulator protein of nanoparticle formation, magnetosome membrane specific F (MmsF), was recently discovered. This predicted integral membrane protein is essential for controlling the monodispersity of the nanoparticles in Magnetospirillum magneticum strain AMB-1. Two MmsF homologs sharing over 60% sequence identity, but showing no apparent impact on particle formation, were also identified in the same organism. We have cloned, expressed, and used these three purified proteins as additives in synthetic magnetite precipitation reactions. Remarkably, these predominantly α-helical membrane spanning proteins are unusually highly stable and water-soluble because they self-assemble into spherical aggregates with an average diameter of 36 nm. The MmsF assembly appears to be responsible for a profound level of control over particle size and iron oxide (magnetite) homogeneity in chemical precipitation reactions, consistent with its indicated role in vivo. The assemblies of its two homologous proteins produce imprecise various iron oxide materials, which is a striking difference for proteins that are so similar to MmsF both in sequence and hierarchical structure. These findings show MmsF is a significant, previously undiscovered, protein additive for precision magnetite nanoparticle production. Furthermore, the self-assembly of these proteins into discrete, soluble, and functional "proteinosome" structures could lead to advances in fields ranging from membrane protein production to drug delivery applications.MmsF | proteinosome | magnetite | magnetosome | in vitro precipitation M agnetic nanoparticles (MNPs) represent an area of intense research due to their diverse and pertinent applications across a range of disciplines and industries. Applications for MNPs include biomedical diagnostics and therapies (1-3), such as MRI contrast reagents, tumor hyperthermia treatments, and magnetically targeted drug delivery, as well as data storage (4) and biotechnology. However, specific magnetic and physical properties of MNPs are critical to the success of each application, with specific size and morphology (with a narrow distribution) being essential considerations. Pure magnetite MNP synthesis under ambient conditions is notoriously difficult to control, with simple precipitations often resulting in a mixture of differently sized and shaped particles with other iron oxide contaminants. This situation can be improved somewhat by using more extreme processes, such as high-temperature incubations or capping surfactants, which favor certain MNP types (5, 6). However, the use of toxic or organic reagents and extreme conditions comes with a high energy and monetary cost, and can limit the biocompatibility of the MNPs for subsequent app...

Metal and metal oxide nanoparticles (NPs) have many uses, and the size, shape and purity of the NPs must be uniform to ensure that the particles function in a known and consistent manner. The synthesis of uniform NPs usually requires high temperatures, high pressures, and harsh chemical reagents, which is both economically and environmentally costly. In nature, biomineralisation is used to produce precise, pure NPs, using far milder reaction conditions and reagents. Recently, a bioinspired approach has been adopted to produce NPs using proteins and peptides that: occur in nature; are artificially selected from a random peptide library by biopanning; or are rationally designed to control NP formation under mild conditions. Here we highlight the recent advances in metal and metal oxide NP binding and synthesis using proteins and peptides. We then investigate bioinspired patterning of NPs onto surfaces. This is done to demonstrate the possible avenues available to develop environmentally friendly, biotemplated devices and nanotechnologies in the future.

Using a surface-based mimic of a magnetosome interior, the biomineralisation protein Mms6 was found to be a more effective nucleator than binder of magnetite nanoparticles, and performs better than its C-terminal region alone.