Hypothetical model for magnetosome membrane formation.

The model suggests that magnetosome membrane proteins (colorful shapes) are recruited to certain sites of the cytoplasmic membrane in a hierarchical manner, with the key proteins MamB, MamM, MamQ and MamL (labeled in shades of blue, yellow and red) acting as nucleating factors, which is followed by recruitment of MamI, MamE, MamO and other magnetosome proteins. Since MamB was found most important for magnetosome membrane (MM) formation, it might act as the initial landmark protein to prime complex formation at certain sited within the cytoplasmic membrane. After a critical size and composition of the multi-protein assembly is reached, the formed lipid-protein complex induces rapid invagination to form the magnetosome lumen. Diffusion from the periplasm into this lumen is blocked. Later, several further magnetosome proteins might become recruited into the MM, which eventually becomes detached to form magnetosome vesicles. The absence of MamB strongly inhibits MM formation, while the absence of either MamM, MamQ or MamL might cause a disturbed protein composition, which leads to the formation of aberrant dense magnetosome membrane-like structures (DMMs) that lack magnetite crystals or blocks magnetosome formation at an immature state.