Die Funktion der CDF-Transporter MamB und MamM beim magnetosomalen Eisentransport in Magnetospirillum gryphiswaldense

Abstract

The ability of M. gryphiswaldense to orient along magnetic field lines is based on magnetosomes, which are magnetite crystals surrounded by a membrane. The specific biomineralization of magnetite particles implies a complex mechanism, involving the uptake, accumulation and precipitation of large amounts of iron. Two putative transporters, MamM and MamB, belonging to the Cation Diffusion Facilitators (CDF) proteins of heavy metal transporters have been found in the subproteom of the magnetosome membrane. In order to reveal their function in magnetite biomineralization in vivo, we constructed deletion mutants of mamM and mamB. The absence of either of these proteins resulted in cells, which are deficient in magnetite formation and impaired in iron accumulation under conditions for magnetite production.The physiological role of MamM and MamB was further studied using GFP fusions to determine their subcellular localization. The results suggest that the integration of MamM and MamB is not restricted to the magnetosome membrane, as MamM-GFP has also been detected in the cytoplasmic membrane during cell cycle. For future in vitro iron uptake studies, a heterologous expression system was established in E. coli. Purified MamM Strep was then reconstituted in liposomes. A co-expression of MamM and MamBStrep with subsequent affinity purification of MamBStrep gave a first hint for a interaction of both proteins.Our results indicate that MamM and MamB are essential for magnetosome formation, thereby mediating iron transport across the magnetosome membrane.