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 |
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Authors: | Uebe René Junge Katja Henn Verena Poxleitner Gabriele Katzmann Emanuel Plitzko Jürgen M Zarivach Raz Kasama Takeshi Wanner Gerhard Pósfai Mihály Böttger Lars Matzanke Berthold Schüler Dirk |
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Institution: | 1. Ludwig Maximillian University Munich, Dept. Biology I, Gro?haderner Str. 2, D‐82152 Martinsried, Germany.;2. Max Planck Institute of Biochemistry, Dept. of Molecular Structural Biology, Am Klopferspitz 18, D‐82152 Martinsried, Germany.;3. Ben Gurion University of the Negev, Dept. of Life Sciences and the National Institute of Biotechnology, POB 653, IL‐84105 Beer‐Sheva, Israel.;4. Technical University of Denmark, Center for Electron Nanoscopy, DK‐2800 Kongens Lyngby, Denmark.;5. University of Pannonia, Dept. of Earth and Environmental Sciences, POB 158, H‐8200 Veszprém, Hungary.;6. University of Lübeck, Isotopes Laboratory, Ratzeburger Allee 160, D‐23538 Lübeck, Germany. |
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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. |
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