Abstract
Green synthesis of precise inorganic nanomaterials is a major challenge. Magnetotactic bacteria biomineralise magnetite nanoparticles (MNPs) within membrane vesicles (magnetosomes), which are embedded with dedicated proteins that control nanocrystal formation. Some such proteins are used in vitro to control MNP formation in green synthesis; however, these membrane proteins self-aggregate, making their production and use in vitro challenging and difficult to scale. Here, we provide an alternative solution by displaying active loops from biomineralisation proteins Mms13 and MmsF on stem-loop coiled-coil scaffold proteins (Mms13cc/MmsFcc). These artificial biomineralisation proteins form soluble, stable alpha-helical hairpin monomers, and MmsFcc successfully controls the formation of MNP when added to magnetite synthesis, regulating synthesis comparably to native MmsF. This study demonstrates how displaying active loops from membrane proteins on coiled-coil scaffolds removes membrane protein solubility issues, while retains activity, enabling a generic approach to readily-expressible, versatile, artificial membrane proteins for more accessible study and exploitation.
Highlights
Green synthesis of precise inorganic nanomaterials is a major challenge
We found that MmsF could affect the crystallisation of magnetite magnetite nanoparticles (MNPs) when added to a simple room temperature coprecipitation synthesis, tightly defining the morphology[24]
We used the TMpred server to estimate the location of membrane spanning helices in MmsF, and membrane specific (Mms)[13] from M. magneticum AMB-1, as well as the acriflavin efflux protein AcrB from E. coli as a negative control (Supplementary Fig. 1) 57
Summary
Green synthesis of precise inorganic nanomaterials is a major challenge. Magnetotactic bacteria biomineralise magnetite nanoparticles (MNPs) within membrane vesicles (magnetosomes), which are embedded with dedicated proteins that control nanocrystal formation. The ultimate goal within this research area is to synthesise magnetic nanoparticles with precise nanoscale control over these properties While this may be possible for a range of sizes and some morphologies, the chemical methods generally utilise toxic precursors and solvents, as well as harsh reaction conditions, which raises issues with biocompatibility of the resulting materials and the environmental sustainability of the process. This latter group of proteins, able to influence the final morphology, size, and characteristics of the mature crystal, represent a promising source of control agent additives to regulate the formation of synthetic magnetite nanoparticles (MNPs) This has been demonstrated with several such magnetosome membrane specific (Mms) proteins, mediating the crystallisation of highly homogeneous MNPs when added to a simple, green, magnetite chemical precipitation reaction[23,24,25]. We found that MmsF could affect the crystallisation of magnetite MNPs when added to a simple room temperature coprecipitation synthesis, tightly defining the morphology[24]
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