title: The HtrA/DegP family protease MamE is a bifunctional protein with roles in magnetosome protein localization and magnetite biomineralization.
abstract: Magnetotactic bacteria contain nanometre-sized, membrane-bound organelles, called magnetosomes, which are tasked with the biomineralization of small crystals of the iron oxide magnetite allowing the organism to use geomagnetic field lines for navigation. A key player in this process is the HtrA/DegP family protease MamE. In its absence, Magnetospirillum magneticum str AMB-1 is able to form magnetosome membranes but not magnetite crystals, a defect previously linked to the mislocalization of magnetosome proteins. In this work we use a directed genetic approach to find that MamE, and another predicted magnetosome-associated protease, MamO, likely function as proteases in vivo. However, as opposed to the complete loss of mamE where no biomineralization is observed, the protease-deficient variant of this protein still supports the initiation and formation of small, 20 nm-sized crystals of magnetite, too small to hold a permanent magnetic dipole moment. This analysis also reveals that MamE is a bifunctional protein with a protease-independent role in magnetosome protein localization and a protease-dependent role in maturation of small magnetite crystals. Together, these results imply the existence of a previously unrecognized 'checkpoint' in biomineralization where MamE moderates the completion of magnetite formation and thus committal to magneto-aerotaxis as the organism's dominant mode of navigating the environment.
authors.affiliation: Department of Molecular and Cell Biology, University of California Berkeley, 111 Koshland Hall, Berkeley, CA 94720, USA.
authors.forename: Anna
authors.initials: A
authors.lastname: Quinlan
authors.forename: Dorothée
authors.initials: D
authors.lastname: Murat
authors.forename: Hojatollah
authors.initials: H
authors.lastname: Vali
authors.forename: Arash
authors.initials: A
authors.lastname: Komeili
mesh_terms: D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism; D052203:Ferrosoferric Oxide / Q000378:metabolism*; D005798:Genes, Bacterial; D006360:Heat-Shock Proteins / Q000378:metabolism*; D008280:Magnetics; D055944:Magnetosomes / Q000201:enzymology*; D042201:Magnetospirillum / Q000201:enzymology* / Q000235:genetics; D008565:Membrane Proteins / Q000096:biosynthesis; D008856:Microscopy, Fluorescence; D016297:Mutagenesis, Site-Directed; D010447:Peptide Hydrolases; D033903:Periplasmic Proteins / Q000378:metabolism*; D016415:Sequence Alignment; D012697:Serine Endopeptidases / Q000378:metabolism*
chemical_list: D001426:Bacterial Proteins; D006360:Heat-Shock Proteins; D008565:Membrane Proteins; D033903:Periplasmic Proteins; D010447:Peptide Hydrolases; C061682:DegP protease; D012697:Serine Endopeptidases; D052203:Ferrosoferric Oxide