Regulation of iron metabolism and magnetite formation in Magnetospirillum gryphiswaldense
Zusammenfassung der Projektergebnisse
Within this project we aimed to characterize the iron uptake routes for biochemical requirements and magnetosome formation. Deletion mutagenesis and careful characterization of the resulting iron uptake mutants revealed that iron for magnetosome formation is at least partially transported through the cytoplasm before accumulation in magnetosome vesicles. Additionally, the synthetic lethal effect of the co-deletion of the two cytoplasmic membrane iron transporters FeoB2 and Mgr0234 suggests the presence of distinct or only poorly connected iron pools for magnetosome formation and biochemical requirements. Next we analyzed candidate proteins required for the magnetosome-directed iron transport. While our data showed that MagA is not involved in magnetosome formation we obtained indirect evidence for an iron transporting activity by the CDF transporter MamM using sitedirected mutagenesis. We also showed that the second magnetosomal CDF protein MamB is required for magnetosome vesicle formation by an unknown mechanism. Furthermore, we showed that MamM directly interacts with MamB and thereby stabilizes it or protects it from degradation as in a mamM deletion mutant MamB levels were found to be drastically reduced. There exists a continuing dispute about the biogenesis of magnetosomes and of magnetite biosynthesis in magnetotactic bacteria (MTB). In particular, the existence, nature and location of possible mineral precursors in the pathway leading to the biosynthesis of magnetite is not clear. One of the possible precursors has been assumed to be bacterioferritin (Bfr). Here, isolation and characterization of bacterioferritin of Magnetospirillum gryphiswaldense (BfrMg) is described employing recombinant techniques. In contrast to typical representatives of the Bfr subgroup of ferritins, characterization of BfrMg disclosed a very atypical heterododecameric assembly of Bfr1Mg and Bfr2Mg subunits. Their amino acid sequences suggest two different functions. Subunit 1 harbors a ferroxidase function. Subunit 2 enables an intersubunit binding of heme. Untypically, BfrMg is membrane-associated. In contrast to phosphate rich amorphous minerals, generally observed in bacterial ferritins, the holoprotein shell of BfrMg harbors 180-360 Fe3+ ions bound as ferrihydrite similar to mammalian ferritins as shown by transmissiob Mössbauer spectroscopy(TMS). Moreover, in situ TMS of a ΔBfrMg mutant uncovered that the presence of ferrihydrite is coupled to the presence of BfrMg. Lack of BfrMg has no impact on magnetite biosynthesis in M. gryphiswaldense (TEM, TMS). As a consequence, ferrihydrite bound in BfrMg is not a precursor of magnetite biosynthesis. A function of BfrMg is found in DNA protection under conditions of oxidative stress.
Projektbezogene Publikationen (Auswahl)
- (2011) 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. Mol. Microbiol. 82(4):818- 835
Uebe, R., K. Junge, V. Henn, G. Poxleitner, E. Katzmann, J. M. Plitzko, R. Zarivach, T. Kasama, G. Wanner, M. Pósfai, L. Böttger, B. Matzanke, and D. Schüler
(Siehe online unter https://doi.org/10.1111/j.1365-2958.2011.07863) - Iron Transport and Biosynthesis of magnetite nanocrystals in magnetosomes of magnetotactic bacteria analysed by Mössbauer spectroscopy. ICBIC 15, 07.08.-12.08.2011, Vancouver, BC, Canada
B.F. Matzanke, L. Böttger, R. Uebe, and D. Schüler
- (2012) The MagA protein of magnetospirilla is not involved in bacterial magnetite biomineralization. J. Bacteriol. 194(5):1018-1023
Uebe, R., V. Henn, and D. Schüler
(Siehe online unter https://doi.org/10.1128/JB.06356-11) - Biosynthesis and Assembly of Magnetic Nanocrystals in Magnetosomes Chains of Magnetotactic Bacteria: The Interplay of Genetics, Biochemistry and Physical Forces. 11th EUROBIC Conference, Granada, Spain, 11.-16.09.2012
B.F. Matzanke, L.H. Böttger, R. Uebe, D. Schüler
- Ferritin-like proteins are not required for magnetosome formation. 4th International Meeting on Magnetotactic Bacteria, Rio de Janeiro, Brazil, 15.-18.09.2014
R. Uebe, K. Jäger, B.F. Matzanke, L.H. Böttger, D. Schüler
- The heterododecameric Bfr of Magnetospirillum gryphiswaldense is membrane-associated and possesses a ferrihydrite core but is not involved in magnetite biosynthesis. Annual Conference of the Association for General and Applied Microbiology, Jena, Germany, 13.-16.03.2016
R. Uebe, K. Jäger, B.F. Matzanke, L.H. Böttger, D. Schüler
