title: Magnetochrome: a c-type cytochrome domain specific to magnetotatic bacteria.
abstract: Magnetotactic bacteria consist of a group of taxonomically, physiologically and morphologically diverse prokaryotes, with the singular ability to align with geomagnetic field lines, a phenomenon referred to as magnetotaxis. This magnetotactic property is due to the presence of iron-rich crystals embedded in lipidic vesicles forming an organelle called the magnetosome. Magnetosomes are composed of single-magnetic-domain nanocrystals of magnetite (Fe(3)O(4)) or greigite (Fe(3)S(4)) embedded in biological membranes, thereby forming a prokaryotic organelle. Four specific steps are described in this organelle formation: (i) membrane specialization, (ii) iron acquisition, (iii) magnetite (or greigite) biocrystallization, and (iv) magnetosome alignment. The formation of these magnetic crystals is a genetically controlled process, which is governed by enzyme-catalysed processes. On the basis of protein sequence analysis of genes known to be involved in magnetosome formation in Magnetospirillum magneticum AMB-1, we have identified a subset of three membrane-associated or periplasmic proteins containing a double cytochrome c signature motif CXXCH: MamE, MamP and MamT. The presence of these proteins suggests the existence of an electron-transport chain inside the magnetosome, contributing to the process of biocrystallization. We have performed heterologous expression in E. coli of the cytochrome c motif-containing domains of MamE, MamP and MamT. Initial biophysical characterization has confirmed that MamE, MamP and MamT are indeed c-type cytochromes. Furthermore, determination of redox potentials for this new family of c-type cytochromes reveals midpoint potentials of -76 and -32 mV for MamP and MamE respectively.
authors.affiliation: Laboratoire de Bioénergétique Cellulaire, CEA/DSV/IBEB, UMR 7265 CNRS/CEA, Université Aix-Marseille, Saint-Paul-lez-Durance, F-13180, France. marina.siponen@cea.fr
authors.forename: Marina I
authors.initials: MI
authors.lastname: Siponen
authors.forename: Géraldine
authors.initials: G
authors.lastname: Adryanczyk
authors.forename: Nicolas
authors.initials: N
authors.lastname: Ginet
authors.forename: Pascal
authors.initials: P
authors.lastname: Arnoux
authors.forename: David
authors.initials: D
authors.lastname: Pignol
mesh_terms: D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D003460:Crystallization; D003574:Cytochrome c Group / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D004579:Electron Transport; D055944:Magnetosomes / Q000235:genetics / Q000378:metabolism* / Q000502:physiology; D042201:Magnetospirillum / Q000235:genetics* / Q000378:metabolism / Q000502:physiology; D008969:Molecular Sequence Data; D010084:Oxidation-Reduction; D017434:Protein Structure, Tertiary
chemical_list: D001426:Bacterial Proteins; D003574:Cytochrome c Group