title: Visualization and structural analysis of the bacterial magnetic organelle magnetosome using atomic force microscopy.
abstract: The unique ability of magnetotactic bacteria to navigate along a geomagnetic field is accomplished with the help of prokaryotic organelles, magnetosomes. The magnetosomes have well-ordered chain-like structures, comprising membrane-enveloped, nano-sized magnetic crystals, and various types of specifically associated proteins. In this study, we applied atomic force microscopy (AFM) to investigate the spatial configuration of isolated magnetosomes from Magnetospirillum magneticum AMB-1 in near-native buffer conditions. AFM observation revealed organic material with a approximately 7-nm thickness surrounding a magnetite crystal. Small globular proteins, identified as magnetosome-associated protein MamA, were distributed on the mica surface around the magnetosome. Immuno-labeling with AFM showed that MamA is located on the magnetosome surface. In vitro experiments showed that MamA proteins interact with each other and form a high molecular mass complex. These findings suggest that magnetosomes are covered with MamA oligomers in near-native environments. Furthermore, nanodissection revealed that magnetosomes are built with heterogeneous structures that comprise the organic layer. This study provides important clues to the supramolecular architecture of the bacterial organelle, the magnetosome, and insight into the function of the proteins localized in the organelle.
authors.affiliation: Department of Physics, Kanazawa University, Kakuma-machi, Kanazawa 920-1192, Japan.
authors.forename: Daisuke
authors.initials: D
authors.lastname: Yamamoto
authors.forename: Azuma
authors.initials: A
authors.lastname: Taoka
authors.forename: Takayuki
authors.initials: T
authors.lastname: Uchihashi
authors.forename: Hideaki
authors.initials: H
authors.lastname: Sasaki
authors.forename: Hiroki
authors.initials: H
authors.lastname: Watanabe
authors.forename: Toshio
authors.initials: T
authors.lastname: Ando
authors.forename: Yoshihiro
authors.initials: Y
authors.lastname: Fukumori
mesh_terms: D001426:Bacterial Proteins / Q000378:metabolism*; D002846:Chromatography, Affinity; D004591:Electrophoresis, Polyacrylamide Gel; D015151:Immunoblotting; D055944:Magnetosomes / Q000648:ultrastructure*; D042201:Magnetospirillum / Q000648:ultrastructure*; D018625:Microscopy, Atomic Force / Q000379:methods*; D046912:Multiprotein Complexes / Q000378:metabolism*
chemical_list: D001426:Bacterial Proteins; D046912:Multiprotein Complexes