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

Abstract

To navigate within the geomagnetic field, magnetotactic bacteria synthesize magnetosomes, which are unique organelles consisting of membrane-enveloped magnetite nanocrystals. In magnetotactic spirilla, magnetosomes become actively organized into chains by the filament-forming actin-like MamK and the adaptor protein MamJ, thereby assembling a magnetic dipole much like a compass needle. However, in Magnetospirillum gryphiswaldense, discontinuous chains are still formed in the absence of MamK. Moreover, these fragmented chains persist in a straight conformation indicating undiscovered structural determinants able to accommodate a bar magnet-like magnetoreceptor in a helical bacterium. Here, we identify MamY, a membrane-bound protein that generates a sophisticated mechanical scaffold for magnetosomes. MamY localizes linearly along the positive inner cell curvature (the geodetic cell axis), probably by self-interaction and curvature sensing. In a mamY deletion mutant, magnetosome chains detach from the geodetic axis and fail to accommodate a straight conformation coinciding with reduced cellular magnetic orientation. Codeletion of mamKY completely abolishes chain formation, whereas on synthetic tethering of magnetosomes to MamY, the chain configuration is regained, emphasizing the structural properties of the protein. Our 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.

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Fig. 1: MamY determines the localization of the magnetosome chain at the geodetic axis of M. gryphiswaldense.
Fig. 2: MamY is essential to support the fragmented magnetosome chains in the mamK deletion mutant.
Fig. 3: MamY localizes as a linear structure along the positive curvature in M. gryphiswaldense cells.
Fig. 4: 3D SIM and PALM reveal that MamY forms a linear structure along the positive curvature.
Fig. 5: Reconstruction of a synthetic MamY-supported magnetosome chain.
Fig. 6: Model for MamY molecular interaction, intracellular polymer formation and localization, and its function as part of the magnetoskeleton.

Data availability

The data that support the findings of this study are available from the corresponding author upon reasonable request.

Code availability

The computer code used to analyse the PALM data is publicly available on https://github.com/GiacomoGiacomelli/mamy-cluster-analysis.

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Acknowledgements

We are grateful to G. Pfeifer (MPI of Biochemistry) for constant support with TEM and Cryo-ET, also to M. Turk for help with TEM. We thank B. Melzer, I. Mai and M. Klein for technical assistance, and we acknowledge T. Zwiener for providing the Mgryph ΔMAI strain. We are thankful to J. Peychl and B. Nitzsche at the MPI-CBG, light microscopy facility, for access to a GE DeltaVision OMX v4 Blaze microscope and to D.J. White of GE Healthcare-Cell Analysis, for applications support, technical specifications for publication and assistance with microscopy on the OMX. We also thank R. Zarivach, Ben-Gurion University of the Negev Beer Sheva, for helpful discussions. We are also grateful to M. Heider, Bayreuth Institute for Macromolecule Research, for technical assistance with scanning electron microscopy and we thank ChromoTek GmbH, Planegg-Martinsried, Germany for providing the mCherry-binding (RBP-) nanobody. Finally, we are deeply thankful to N. Albrecht for protein purification and help with DLS analysis. This work was supported by the Deutsche Forschungsgemeinschaft Grants Schu1080/9-2 (to D.S.), INST 86/1452 (to M.B.), INST 160/646-1, TRR174 project 5 (to M.B.) and has received funding from the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme (grant agreement no. 692637 (to D.S.)).

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M.T.-N., D.S. and F.D.M. conceived and designed research. M.T.-N., G.G., O.R., S.B. and F.D.M. performed experiments. M.T.-N. and F.D.M. performed SIM imaging. M.T.-N. and F.D.M. performed TEM and fluorescence microscopy. G.G. and M.T.-N. established and carried out PALM. G.G. created the single-molecule clustering algorithm and generated the PALM images. G.G., M.T.-N. and M.B. analysed PALM data. M.T.-N. performed cryo-ET; M.T.-N. and J.M.P. analysed the data. F.D.M. performed scanning electron microscopy with the help of M. Heider. M.T.-N. and M.B. analysed DLS data. M.T.-N. and F.D.M. analysed the whole dataset and wrote the manuscript. All authors discussed the results and commented on the manuscript.

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Correspondence to Frank-Dietrich Müller.

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Supplementary information

Supplementary Information

Supplementary Figs. 1–13, Supplementary Notes, Supplementary Discussion, Supplementary Video legends, Supplementary Tables 1–3 and Supplementary References.

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Supplementary Video 1

Cryo-ET and 3D rendering of a WT cell.

Supplementary Video 2

Cryo-ET and 3D rendering of a ΔmamY cell.

Supplementary Video 3

3D SIM of mCherry-MamY.

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Toro-Nahuelpan, M., Giacomelli, G., Raschdorf, O. et al. MamY is a membrane-bound protein that aligns magnetosomes and the motility axis of helical magnetotactic bacteria. Nat Microbiol 4, 1978–1989 (2019). https://doi.org/10.1038/s41564-019-0512-8

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