Assembly of a prokaryotic organelle by Tic20-like proteins

• Applicant: Dr. Rene Uebe
• Subject Area: Metabolism, Biochemistry and Genetics of Microorganisms
• Term: from 2019 to 2023
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 414946895

• Final Report Year: 2025

Final Report Abstract

Magnetotactic bacteria (MTB) form intracellular magnetite crystals within specialized organelles called magnetosomes. However, the molecular mechanisms underlying magnetosome formation remained largely unknown. Since magnetosomal MamF-like proteins share an evolutionary link to Tic20, a core component of plastid biogenesis, we investigated their role in magnetosome formation. After establishing an optimized protocol for magnetosome purification, we identified eleven proteins significantly depleted in magnetosomes of a mutant lacking all MamF-like proteins using proteomic analyses. Among these proteins, MamD, MamJ, and Mms5 showed the strongest reduction and interacted with MamF-like proteins in bacterial two-hybrid assays. Live-cell imaging and biochemical assays revealed that MamF-like proteins mediate magnetosome targeting through a diffusion-and-capture mechanism. Magnetosome targeting of MamJ essentially requires a glycine-rich C-terminal putative transmembrane helix also found in MamD and Mms5. Consistently, these proteins can only be extracted from magnetosomes using detergents indicating stable membrane integration. While previous models proposed that MFPs directly mediate magnetite biomineralization, our results indicate they instead function as organelle-specific translocases, integrating substrate proteins into the magnetosome membrane. Our findings thus provide new insights into the mechanisms underlying magnetosome formation and highlight an evolutionary connection between bacterial and eukaryotic organelles, expanding our understanding of prokaryotic organelle biogenesis.

Publications

• 6 THE FORMATION OF IRON BIOMINERALS IN MAGNETOTACTIC BACTERIA. Metals, Microbes, and Minerals - The Biogeochemical Side of Life, 159-184. De Gruyter.
  Uebe, René & Schüler, Dirk
  
• Identification and elimination of genomic regions irrelevant for magnetosome biosynthesis by large-scale deletion in Magnetospirillum gryphiswaldense. BMC Microbiology, 21(1).
  Zwiener, Theresa; Mickoleit, Frank; Dziuba, Marina; Rückert, Christian; Busche, Tobias; Kalinowski, Jörn; Faivre, Damien; Uebe, René & Schüler, Dirk
  
• Multifunktionale bakterielle Nanomagnete für Biotechnologie und Medizin. BIOspektrum, 27(4), 442–444.
  Mickoleit, Frank; Rosenfeldt, Sabine; Schenk, Anna S.; Schüler, Dirk & Uebe, René
  
• Synchrotron‐Based Nano‐X‐Ray Absorption Near‐Edge Structure Revealing Intracellular Heterogeneity of Iron Species in Magnetotactic Bacteria. Small Science, 2(3).
  Chevrier, Daniel M.; Cerdá-Doñate, Elisa; Park, Yeseul; Cacho-Nerin, Fernando; Gomez‐Gonzalez, Miguel; Uebe, René & Faivre, Damien
  
• Towards standardized purification of bacterial magnetic nanoparticles for future in vivo applications. Acta Biomaterialia, 120, 293-303.
  Rosenfeldt, Sabine; Mickoleit, Frank; Jörke, Cornelia; Clement, Joachim H.; Markert, Simon; Jérôme, Valérie; Schwarzinger, Stephan; Freitag, Ruth; Schüler, Dirk; Uebe, René & Schenk, Anna S.
  
• Silent gene clusters encode magnetic organelle biosynthesis in a non-magnetotactic phototrophic bacterium. The ISME Journal, 17(3), 326-339.
  Dziuba, M. V.; Paulus, A.; Schramm, L.; Awal, R. P.; Pósfai, M.; Monteil, C. L.; Fouteau, S.; Uebe, R. & Schüler, D.
  
• MamF-like proteins are distant Tic20 homologs involved in organelle assembly in bacteria. Nature Communications, 15(1).
  Paulus, Anja; Ahrens, Frederik; Schraut, Annika; Hofmann, Hannah; Schiller, Tim; Sura, Thomas; Becher, Dörte & Uebe, René
  
• Biogenese magnetischer Organellen in Bakterien. BIOspektrum, 31(4), 390-392.
  Uebe, René