Control of the morphology and size of magnetite particles with peptides mimicking the Mms6 protein from magnetotactic bacteria

Mms6 is a dominant protein that tightly associates with the surface of bacterial magnetites in Magnetospirillum magneticum AMB-1. The protein has previously been shown to mediate the formation of uniform magnetite crystals of cubo-octahedral morphology consisting of (1 1 1) and (1 0 0) crystal faces with a narrow size distribution during chemical magnetite synthesis. In order to understand the role of this protein in chemical magnetite synthesis, magnetite formation was investigated using synthetic peptides mimicking the Mms6 protein. Particles that were synthesized in the presence of short peptides harbouring the C-terminal acidic region of Mms6 exhibited a spherical morphology with circularities of 0.70-0.90 similar to those of bacterial magnetites and particles formed in the presence of the Mms6 protein. In contrast, a rectangular morphology with circularities of 0.60-0.85 were obtained when other peptides were used for synthesis. The results indicated that the C-terminal region of the Mms6 protein has significant control over the morphology of magnetite crystals in the chemical synthetic method. This method can, therefore, be useful as an alternative method of controlling the size and morphology of magnetite crystals under ambient conditions.