Visualization of Iron‐Binding Micelles in Acidic Recombinant Biomineralization Protein, MamC

Abstract

Biological macromolecules are utilized in low-temperature synthetic methods to exert precise control over nanoparticle nucleation and placement. They enable low-temperature formation of a variety of functional nanostructured materials with properties often not achieved via conventional synthetic techniques. Here we report on thein situvisualization of a novel acidic bacterial recombinant protein, MamC, commonly present in the magnetosome membrane of several magnetotactic bacteria, includingMagnetococcus marinus, strain MC-1. Our findings provide an insight into the self-assembly of MamC and point to formation of the extended protein surface, which is assumed to play an important role in the formation of biotemplated inorganic nanoparticles. The self-organization of MamC is compared to the behavior of another acidic recombinant iron-binding protein, Mms6.

Size control of in vitro synthesized magnetite crystals by the MamC protein of Magnetococcus marinus strain MC-1

“…These results are in agreement with MamCnts (control) and in the presence of 10 and 60 μg/mL or MamCnts, and c aqueous synthesis without MamC (control) and in the presence of 10 and 60 μg/mL or MamC. The data were normalized to the magnetization values at 300 K. Mms6 data from Wang et al (2012) are plotted for comparison the observations of Kashyap et al (2014) who found that MamC forms micelles in solution and, when a solution of Fe 3+ is delivered, cations bind to the negatively charged surface of the micelle creating a highly concentrated area of Fe 3+ . Magnetite nucleation would then occur preferentially at the surface of the protein micelles, potentially permitting crystal growth with virtually no space limitation.…”

Self-assembled MmsF proteinosomes control magnetite nanoparticle formation in vitro

“…Magnetosome-associated proteins that have been previously characterized, such as Mms6 and, recently, Mms13 (MamC), are also predicted to span the MM. These proteins are expressed in E. coli as insoluble inclusion bodies but, interestingly, can be denatured and refolded into soluble aggregated structures, displaying iron binding capabilities (13,25,26). Coupled with our data, this finding points to a pattern of soluble behavior between various magnetosome-associated membrane proteins.…”

“…It was also noted in that study that MamF produced large, SDSresistant, oligomeric species in SDS/PAGE experiments (30), which hinted that these proteins might assemble into aggregated stable species in vitro. Coupled with the work described in this paper and the self-assembly properties of other magnetosome proteins (25,26), we speculate that MmsF and its homologs might assemble within the MM, forming strong packing interactions between themselves. This assembly may tessellate a tightly packed and ordered island of protein within the lipid membrane that could display the active surface loops and termini discussed above in a precise pattern on the interior face of the magnetosome.…”

In-situ liquid phase TEM observations of nucleation and growth processes

“…This technique has been applied to a broad range of materials systems, including metallic and semiconductor nanoparticles and nanowires [9,, geochemical and biological minerals [8,10,[40][41][42], electrochemical systems (see Ref. [17] for a recent review), protein complexes [40,43,44], viruses, and self-assembling systems of organic films, vesicles, macromolecules, and nanoparticles [10,29,43,[45][46][47][48]. Moreover, nucleation and growth events can be triggered within LP-TEM liquid cells using a number of methods, including mixing of reagents [41], in-diffusion of a gaseous reactant [10], electrochemical reaction [17,18], heating [49], and through the radiolytic effects of the electron beam [50][51][52].…”