Structural insight into magnetochrome-mediated magnetite biomineralization

The magnetosome-associated protein mamP is an iron oxidase that reveals a unique arrangement of a self-plugged PDZ domain fused to two magnetochrome domains, defining a new class of c -type cytochrome exclusively found in magnetotactic bacteria. Structure of magnetosome protein MamP Magnetotactic bacteria use a specialized organelle known as the magnetosome, a biomineralized crystal of magnetite (Fe( II )Fe( III ) 2 O 4 ) or greigite (Fe( II )Fe( III ) 2 S 4 ), to sense and align along the Earth's magnetic field. This paper presents the X-ray crystal structure of the magnetosome-associated protein MamP, revealing a unique arrangement of a self-plugged PDZ domain fused to two magnetochrome domains. The authors also establish that MamP is an iron oxidase that contributes to the formation of iron( III ) ferrihydrite, and is therefore important for mechanisms of iron management during magnetosome biogenesis. Magnetotactic bacteria align along the Earth’s magnetic field using an organelle called the magnetosome, a biomineralized magnetite (Fe( ii )Fe( iii ) 2 O 4 ) or greigite (Fe( ii )Fe( iii ) 2 S 4 ) crystal embedded in a lipid vesicle. Although the need for both iron( ii ) and iron( iii ) is clear, little is known about the biological mechanisms controlling their ratio 1 . Here we present the structure of the magnetosome-associated protein MamP and find that it is built on a unique arrangement of a self-plugged PDZ domain fused to two magnetochrome domains, defining a new class of c -type cytochrome exclusively found in magnetotactic bacteria. Mutational analysis, enzyme kinetics, co-crystallization with iron( ii ) and an in vitro MamP-assisted magnetite production assay establish MamP as an iron oxidase that contributes to the formation of iron( iii ) ferrihydrite eventually required for magnetite crystal growth in vivo . These results demonstrate the molecular mechanisms of iron management taking place inside the magnetosome and highlight the role of magnetochrome in iron biomineralization.