Magnetosomes Are Cell Membrane Invaginations Organized by the Actin-Like Protein MamK

  title={Magnetosomes Are Cell Membrane Invaginations Organized by the Actin-Like Protein MamK},
  author={Arash Komeili and Zhuo-Yue Li and Dianne K. Newman and Grant J. Jensen},
  pages={242 - 245}
Magnetosomes are membranous bacterial organelles sharing many features of eukaryotic organelles. Using electron cryotomography, we found that magnetosomes are invaginations of the cell membrane flanked by a network of cytoskeletal filaments. The filaments appeared to be composed of MamK, a homolog of the bacterial actin-like protein MreB, which formed filaments in vivo. In a mamK deletion strain, the magnetosome-associated cytoskeleton was absent and individual magnetosomes were no longer… 

Structure of the magnetosome‐associated actin‐like MamK filament at subnanometer resolution

While MamK is closest in sequence to the bacterial actin MreB, the longitudinal contacts along each MamK strand most closely resemble those of eukaryotic actin, which gives rise to the nonstaggered architecture.

Biogenesis and subcellular organization of the magnetosome organelles of magnetotactic bacteria.

Polymerization of the Actin-Like Protein MamK, Which Is Associated with Magnetosomes

It is demonstrated that MamK polymerizes into filamentous bundles in vitro and is used as an antigen to generate the anti-MamK antibody.

Biogenesis of actin-like bacterial cytoskeletal filaments destined for positioning prokaryotic magnetic organelles

The results demonstrate the mechanism of biogenesis of prokaryotic cytoskeletal filaments that are structurally and functionally distinct from the known MreB and ParM filaments and prove the authenticity of the MamK filaments.

Segregation of prokaryotic magnetosomes organelles is driven by treadmilling of a dynamic actin-like MamK filament

A novel mechanism for prokaryotic organelle segregation is proposed that, similar to the type-II bacterial partitioning system of plasmids, relies on the action of cytomotive actin-like filaments together with specific connectors, which transport the magnetosome cargo in a fashion reminiscent of eukaryoticActin-organelle transport and segregation mechanisms.

MamY is a membrane-bound protein that aligns magnetosomes and the motility axis of helical magnetotactic bacteria

The results suggest MamY is membrane-anchored mechanical scaffold that is essential to align the motility axis of magnetotactic spirilla with their magnetic moment vector and to perfectly reconcile magnetoreception with swimming direction.

Prokaryotic Cytoskeletons

The protofilament structures and polymerisation activities of various actin-like, tubulin-like and ESCRT-like proteins of prokaryotes closely resemble their eukaryotic counterparts but show greater diversity.

The Bacterial Actin MamK

It is demonstrated that MamK is an ATPase that, in the presence of ATP, assembles rapidly into filaments that disassemble once ATP is depleted, which is consistent with observations indicating that accessory factors are required for filament disassembly and for spatial organization of filaments in vivo.

Greigite magnetosome membrane ultrastructure in 'Candidatus Magnetoglobus multicellularis'.

Observations of cell membrane invaginations, the trilaminar membrane structure of immature magnetosomes, and empty vesicles together suggested that greigite magnetosome formation begins by invagination of the cell membrane, as has been proposed for magnetite magnetOSomes.

Genetics and cell biology of magnetosome formation in magnetotactic bacteria

A total of 28 conserved genes present in various magnetic bacteria were identified to be specifically associated with the magnetotactic phenotype, most of which are located in the genomic magnetosome island.



Magnetosome vesicles are present before magnetite formation, and MamA is required for their activation.

Together, these results suggest that the magnetosome precisely coordinates magnetite biomineralization and can serve as a model system for the study of organelle biogenesis in noneukaryotic cells.

Cryo-Electron Tomography Reveals the Cytoskeletal Structure of Spiroplasma melliferum

Cryo–electron tomography was used to study the three-dimensional structure of Spiroplasma melliferum cells in a close-to-native state and it was showed that these cells possess two types of filaments arranged in three parallel ribbons underneath the cell membrane.

Prokaryotic origin of the actin cytoskeleton

It is demonstrated that the bacterial MreB protein assembles into filaments with a subunit repeat similar to that of F-actin—the physiological polymer of eukaryotic actin, demonstrating that M reB and actin are very similar in three dimensions.

Increasing complexity of the bacterial cytoskeleton.

Characterization of the bacterial magnetosome membrane.

Intact magnetosomes of Aquaspirillum magnetotacticum were purified from broken cells by a magnetic separation technique and revealed the magnetite to be enclosed by a lipid bilayer admixed with proteins.

Identification of Organelles in Bacteria Similar to Acidocalcisomes of Unicellular Eukaryotes*

It is reported that the volutin granules of Agrobacterium tumefaciens possess properties similar to the acidocalcisomes, a compound isolated from a marine bacterium that has been shown to uncouple proton pyrophosphatase activity acting as a chloride/proton symport.

Biochemical and Proteomic Analysis of the Magnetosome Membrane in Magnetospirillum gryphiswaldense

Several magnetosome proteins found in Magnetospirillum gryphiswaldense display repetitive or highly acidic sequence patterns, which are known from other biomineralizing systems and thus may have relevance for magnetite formation.

F‐actin‐like filaments formed by plasmid segregation protein ParM

It is shown here that ParM polymerizes into double helical protofilaments with a longitudinal repeat similar to filamentous actin (F‐actin) and MreB filaments that maintain the cell shape of non‐spherical bacteria.