Structure–Function of MamC Loop and Its Effect on the in Vitro Precipitation of Biomimetic Magnetite Nanoparticles

MamC, an integral protein of the magnetosome membrane, has recently been proposed as a strong candidate to produce biomimetic (magnetosome-like) magnetite nanoparticles that could be used as an alternative to magnetosomes in different applications such as nanocarriers. The secondary structure of the protein contains two helical transmembrane domains connected by an α-helical loop oriented toward the magnetosome lumen. In this loop, the residues Glu66 and Asp70 seem to be responsible for a template effect that controls the nucleation and/or growth of biomimetic nanoparticles in vitro. In the present study, we have introduced a double mutation, E66A and D70A, in the sequence of MamC while working, for the first time, with the full-length protein. Our results show that this double mutation does not affect either the conformation or the stability of MamC, but it indeed makes the protein lose its functionality in terms of controlling the process of magnetite biomineralization in vitro. The present study shows that the ionotropic effect is not enough to account for the effect of the wild type MamC on the formation of BMNPs, but the template effect seems to rule such a process. Also, it shows that no other region of MamC is involved in controlling the process of magnetite biomineralization. Moreover, the stability of MamC in solution is only marginal, probably due to the absence of contacts established with the membrane lipid bilayer.