Required for correct biomineralization of the magnetosome, may be involved in redox control of biomineralization. May function with MamY, MamZ amd Mms6. Binds 2 heme groups per subunit via the 2 magnetochrome (MCR) motifs. This bacteria makes up to 20 cubo-octahedral magnetosomes of about 45 nm in diameter which contain membrane-bound crystals of magnetite (Fe(3)O(4)). Belongs to the magnetosome MamX family.