Andrea E. Rawlings

Biotemplated magnetic nanoparticle arrays

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.

Innovation through imitation: biomimetic, bioinspired and biokleptic research

While biomimetic research is becoming increasingly popular the term is being used for a broader range of research and it is becoming more difficult for researchers to understand and define. In this opinion article we discuss how biomimetic research overlaps with and differs from the complementary fields of biotechnology, biokleptic and bioinspired research as we attempt to describe each area with definitions, examples and discussion. What makes research biomimetic, bioinspired or biokleptic is put under scrutiny as we ask: can different components, parts and processes of an experiment be categorised separately? What is the difference between a biological and synthetic system/component? Is the scientist or biology in control? The answers to which aim to untangle the subtleties of the biomimetics field.

Self-assembled MmsF proteinosomes control magnetite nanoparticle formation in vitro

Significance Magnetotactic bacteria produce morphologically precise magnetite nanoparticles within organelles termed “magnetosomes.” Biomineralization proteins tightly regulate crystallization of these nanoparticles. A master protein regulator of particle morphology in vivo, magnetosome membrane specific F (MmsF), has recently been discovered. In this study, we purified MmsF and two homologous proteins from Magnetospirillum magneticum strain AMB-1. MmsF imposes strict control over the formation of magnetite nanoparticles when added to chemical precipitation reactions, whereas the highly similar homologues produce alternative iron oxides with less desirable magnetic properties. Remarkably, these intrinsic membrane proteins with three membrane-spanning regions are water-soluble and self-assemble in vitro into nanoscale “proteinosomes.” We speculate that self-assembly exists in vivo and might be required for the activity of the protein. Magnetotactic bacteria synthesize highly uniform intracellular magnetite nanoparticles through the action of several key biomineralization proteins. These proteins are present in a unique lipid-bound 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.

Nanomagnetic Arrays Formed with the Biomineralization Protein Mms6

Many Modern Technologies, such as High Density Data Storage, Require Monodispersed Magnetic Nanoparticles (MNPs), which Have a Consistent Magnetic Behavior, Specifically Immobilized onto a Patterned Surface. Current Methods for Synthesizing Uniform Mnps Require High Temperatures and Harsh Chemicals, which Is Not Environmentally Friendly. Also, the Particles Are Expensive to Make and Expensive to Pattern Using Conventional Lithography Methods. Magnetic Bacteria Are Able to Synthesize Consistent Mnps in Vivo Using Biomineralization Proteins inside Magnetosome Vesicles to Control Particle Size and Shape and Make Single Domain Mnps. Mms6 Is a Biomineralization Protein that Is Able to Template Cubo-Octahedral MNP Formation in Vitro. it Is Thought the N-Terminus Helps Integrate the Protein into the Magnetosome Membrane, and the C-Terminus Interacts with Magnetite during Nucleation and/or MNP Growth. by Selectively Attaching Mms6 to a Patterned Self Assembled Monolayer via the N-Terminus, Patterns of Uniform Magnetite Mnps Are Templated in Situ. this Also Requires Careful Selection of the Mineralization Solution Used to Mineralize the Patterned Mms6. here we Evaluate some Low Temperature (room Temperature to < 100°C) Methods of Magnetite Formation to Produce Monodispersed Magnetite Mnps onto Immobilized Mms6. Room Temperature Co-Precipitation (RTCP) Was Found to Be Unsuitable, as the Magnetite Does Not Form on the Immobilized Mms6, but Appears to Form Rapidly as Base Is Added. Partial Oxidation of Ferrous Hydroxide (POFH) Was Found to Be Able to Form Consistent Magnetite Mnps on the Immobilized Mms6, as the Reactants Gradually Mature to Form Magnetite over a few Hours (at 80°C) or a few Days (room Temperature). by Carefully Controlling the Type of Base Used, the Ratio of the Reactants and the Temperature and Duration of the POFH Mineralization Reaction, this System Was Optimized to Produce Consistent Mnps (340 ± 54 Nm, Coercivity 109 Oe) on the Immobilized Mms6, with Scarcely any Mineralization on the Anti-Biofouling Background. the Mnps Are Ferrimagnetic, and Appear to Be Exchange Coupled across Multiple Particles in MFM Measurements. the Specificity of this Method towards Precise Magnetite Mineralization under Relatively Mild Conditions May Be Adapted to Nanoscale Patterning of Multiple Biotemplated Materials, by Using other Biomineralization Proteins or Peptides. this Would Allow the Fabrication of Cheaper, More Environmentally Friendly Components for Devices of the Future.

Ferrous Iron Binding Key to Mms6 Magnetite Biomineralisation: A Mechanistic Study to Understand Magnetite Formation Using pH Titration and NMR Spectroscopy.

Abstract Formation of magnetite nanocrystals by magnetotactic bacteria is controlled by specific proteins which regulate the particles’ nucleation and growth. One such protein is Mms6. This small, amphiphilic protein can self‐assemble and bind ferric ions to aid in magnetite formation. To understand the role of Mms6 during in vitro iron oxide precipitation we have performed in situ pH titrations. We find Mms6 has little effect during ferric salt precipitation, but exerts greatest influence during the incorporation of ferrous ions and conversion of this salt to mixed‐valence iron minerals, suggesting Mms6 has a hitherto unrecorded ferrous iron interacting property which promotes the formation of magnetite in ferrous‐rich solutions. We show ferrous binding to the DEEVE motif within the C‐terminal region of Mms6 by NMR spectroscopy, and model these binding events using molecular simulations. We conclude that Mms6 functions as a magnetite nucleating protein under conditions where ferrous ions predominate.

A novel design strategy for nanoparticles on nanopatterns: interferometric lithographic patterning of Mms6 biotemplated magnetic nanoparticles

Top-down surface patterning technique, interferometric lithography, is combined with bottom-up magnetite nanoparticle biomineralisation using Mms6 to form magnetic nanoscale arrays.

Membrane proteins: always an insoluble problem?

Membrane proteins play crucial roles in cellular processes and are often important pharmacological drug targets. The hydrophobic properties of these proteins make full structural and functional characterization challenging because of the need to use detergents or other solubilizing agents when extracting them from their native lipid membranes. To aid membrane protein research, new methodologies are required to allow these proteins to be expressed and purified cheaply, easily, in high yield and to provide water soluble proteins for subsequent study. This mini review focuses on the relatively new area of water soluble membrane proteins and in particular two innovative approaches: the redesign of membrane proteins to yield water soluble variants and how adding solubilizing fusion proteins can help to overcome these challenges. This review also looks at naturally occurring membrane proteins, which are able to exist as stable, functional, water soluble assemblies with no alteration to their native sequence.

Crystallizing the function of the magnetosome membrane mineralization protein Mms6.

The literature on the magnetosome membrane (MM) protein, magnetosome membrane specific6 (Mms6), is reviewed. Mms6 is native to magnetotactic bacteria (MTB). These bacteria take up iron from solution and biomineralize magnetite nanoparticles within organelles called magnetosomes. Mms6 is a small protein embedded on the interior of the MM and was discovered tightly associated with the formed mineral. It has been the subject of intensive research as it is seen to control the formation of particles both in vivo and in vitro. Here, we compile, review and discuss the research detailing Mms6’s activity within the cell and in a range of chemical in vitro methods where Mms6 has a marked effect on the composition, size and distribution of synthetic particles, with approximately 21 nm in size for solution precipitations and approximately 90 nm for those formed on surfaces. Furthermore, we review and discuss recent work detailing the structure and function of Mms6. From the evidence, we propose a mechanism for its function as a specific magnetite nucleation protein and summaries the key features for this action: namely, self-assembly to display a charged surface for specific iron binding, with the curvature of the surfaces determining the particle size. We suggest these may aid design of biomimetic additives for future green nanoparticle production.

Novel Methods for the Synthesis of Magnetic Nanoparticles

Abstract This chapter presents methods for the synthesis of magnetic nanoparticles with a special emphasis on new and emerging methods. The scope covers, chemical, biological and physical methods that are able to produce nanoparticles with a narrow size distribution including elements, oxides and bimetallic particles. The methods described can prepare nanoparticle assemblies either as hydrosols or embedded in solid matrices. Thus materials cover the entire scope of this volume, which includes high-performance solid magnetic materials for engineering applications and nanoparticle liquid suspensions for medical and environmental applications.

Reply to the ‘Comment on “Innovation through imitation: Biomimetic, bioinspired and biokleptic research”’ by M. Drack and I. C. Gebeshuber, Soft Matter, 2013, 9, DOI: 10.1039/c2sm26722e

A response to the comments raised by Drack et al. in their reply to the discussion of biomimicry and related fields set out in our opinions paper Rawlings et al. Here we appreciate the common views we share and welcome the clarity this gives, and we discuss and question some of their criticisms of the original piece and clarify our opinion in this area.