Essential for magnetosome formation; required for stable accumulation of MamB (PubMed:22007638). May nucleate iron crystal formation (Probable). Probably binds and transports iron. Binds divalent cations, possibly up to 3 Zn(2+) per dimer in vitro, probably iron in vivo (Probable) (PubMed:30811856). One of 7 genes (mamLQBIEMO) able to induce magnetosome membrane biogenesis; coexpression of mamLQRBIEMO in a deletion of the 17 gene mamAB operon restores magnetosome vesicle formation but not magnetite biosynthesis (PubMed:27286560). Forms homodimers via its C-terminal domain (CTD) in the presence of metal cations (Probable). Interacts with MamB via their CTD (PubMed:22007638, PubMed:29243866) (Probable). Isolated CTD forms homodimers (PubMed:24658343, PubMed:24819161, PubMed:27550551, PubMed:30811856). Localizes with magnetosomes in a straight line running through the center of the cell. Part of the probable 17 gene mamAB operon. The C-terminal domain (CTD) is probably responsible for hetero- and homodimerization; it assumes a V-shaped, dimeric metallo-chaperone-like fold that can open and close. Val-260 forms the hinge between the dimers. Binds up to 3 divalent metal cations (probably iron in vivo); upon binding there is a conformational shift to a tighter dimer (PubMed:24658343, PubMed:30811856) (Probable). If the CTD cannot fold correctly the function of the whole protein is decreased, suggesting the CTD confers functionality on the transmembrane domain (TMD), perhaps activated by ligand binding to the CTD (Probable). Single gene disruption has no growth defects, no accumulation of magnetite, forms empty intracellular magnetosome vesicles, decreased levels of MamB, mislocation of MamC in 1-3 foci or rarely in a shortened chain (PubMed:22007638). Magnetosome vesicles are fewer and smaller, aligned in a chain with the filament, only a few have very small crystals. Other, possibly precursor magnetosome vesicles are visible. MamI mislocalized to cell inner membrane or in 1 to a few patches (PubMed:27286560). Deletion of approximately 80 kb of DNA, including this operon, leads to cells that are non-magnetic, lack internal membrane systems, grow poorly, have reduced mobility and take-up and accumulate iron poorly (PubMed:13129949). This bacteria makes up to 60 cubo-octahedral magnetosomes of about 45 nm in diameter which contain membrane-bound crystals of magnetite (Fe(3)O(4)). Expression of just the minimal mamAB gene cluster (MGMSRv2__2365 to MGMSRv2__2381), including this gene, is sufficient to form a minimal magnetosome chain with small magnetite particles. Cation diffusion facilitator (CDF) transporters all have similar domain structure. By recreating in MamM mutations known in paralogous human zinc transporters (Znt-8, SLC30A8 and ZnT-10, SLC30A10), information about the effects of these mutations can be learned. Belongs to the cation diffusion facilitator (CDF) transporter (TC 2.A.4) family. A sense of direction - Issue 217 of September 2019