title: The cation diffusion facilitator proteins MamB and MamM of Magnetospirillum gryphiswaldense have distinct and complex functions, and are involved in magnetite biomineralization and magnetosome membrane assembly.
abstract: Magnetotactic bacteria form chains of intracellular membrane-enclosed, nanometre-sized magnetite crystals for navigation along the earth's magnetic field. The assembly of these prokaryotic organelles requires several specific polypeptides. Among the most abundant proteins associated with the magnetosome membrane of Magnetospirillum gryphiswaldense are MamB and MamM, which were implicated in magnetosomal iron transport because of their similarity to the cation diffusion facilitator family. Here we demonstrate that MamB and MamM are multifunctional proteins involved in several steps of magnetosome formation. Whereas both proteins were essential for magnetite biomineralization, only deletion of mamB resulted in loss of magnetosome membrane vesicles. MamB stability depended on the presence of MamM by formation of a heterodimer complex. In addition, MamB was found to interact with several other proteins including the PDZ1 domain of MamE. Whereas any genetic modification of MamB resulted in loss of function, site-specific mutagenesis within MamM lead to increased formation of polycrystalline magnetite particles. A single amino acid substitution within MamM resulted in crystals consisting of haematite, which coexisted with magnetite crystals. Together our data indicate that MamM and MamB have complex functions, and are involved in the control of different key steps of magnetosome formation, which are linked by their direct interaction.
authors: Ludwig Maximillian University Munich, Dept. Biology I, Großhaderner Str. 2, D-82152 Martinsried, Germany.
authors: René
authors: R
authors: Uebe
authors: Katja
authors: K
authors: Junge
authors: Verena
authors: V
authors: Henn
authors: Gabriele
authors: G
authors: Poxleitner
authors: Emanuel
authors: E
authors: Katzmann
authors: Jürgen M
authors: JM
authors: Plitzko
authors: Raz
authors: R
authors: Zarivach
authors: Takeshi
authors: T
authors: Kasama
authors: Gerhard
authors: G
authors: Wanner
authors: Mihály
authors: M
authors: Pósfai
authors: Lars
authors: L
authors: Böttger
authors: Berthold
authors: B
authors: Matzanke
authors: Dirk
authors: D
authors: Schüler
mesh_terms: D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D004252:DNA Mutational Analysis; D052203:Ferrosoferric Oxide / Q000378:metabolism*; D017353:Gene Deletion; D007425:Intracellular Membranes / Q000378:metabolism*; D055944:Magnetosomes / Q000378:metabolism*; D042201:Magnetospirillum / Q000235:genetics / Q000378:metabolism*; D008969:Molecular Sequence Data; D050505:Mutant Proteins / Q000235:genetics / Q000378:metabolism; D025941:Protein Interaction Mapping; D055503:Protein Multimerization; D055550:Protein Stability; D017386:Sequence Homology, Amino Acid
chemical_list: D001426:Bacterial Proteins; D050505:Mutant Proteins; D052203:Ferrosoferric Oxide