Might be involved in magnetite crystal growth. Tightly associated with magnetite crystals. Seen in gels as a band of about 5 kDa, with an N-terminus that corresponds to residue 8, suggesting it may undergo N-terminal cleavage. Still forms magnetite crystals, which are about half the size of wild-type but have a wild-type surface. 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 MamD/Mms5 family. Extended N-terminus.