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J Biol Chem. 2016 Aug 19;291(34):17941-52. doi: 10.1074/jbc.M116.731000. Epub 2016 Jun 14.

Magnetite Biomineralization in Magnetospirillum magneticum Is Regulated by a Switch-like Behavior in the HtrA Protease MamE.

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From the Departments of Plant and Microbial Biology and.
the California Institute for Quantitative Biosciences, and the QB3/Chemistry Mass Spectrometry Facility, and the University of California, Berkeley, California 94720 and.
the Department of Molecular Genetics, Terrance Donnelly Centre for Cellular and Biomedical Research, University of Toronto, Toronto, Ontario M5S 3E1, Canada.
Molecular and Cell Biology.
From the Departments of Plant and Microbial Biology and the California Institute for Quantitative Biosciences, and Molecular and Cell Biology,


Magnetotactic bacteria are aquatic organisms that produce subcellular magnetic particles in order to orient in the earth's geomagnetic field. MamE, a predicted HtrA protease required to produce magnetite crystals in the magnetotactic bacterium Magnetospirillum magneticum AMB-1, was recently shown to promote the proteolytic processing of itself and two other biomineralization factors in vivo Here, we have analyzed the in vivo processing patterns of three proteolytic targets and used this information to reconstitute proteolysis with a purified form of MamE. MamE cleaves a custom peptide substrate with positive cooperativity, and its autoproteolysis can be stimulated with exogenous substrates or peptides that bind to either of its PDZ domains. A misregulated form of the protease that circumvents specific genetic requirements for proteolysis causes biomineralization defects, showing that proper regulation of its activity is required during magnetite biosynthesis in vivo Our results represent the first reconstitution of the proteolytic activity of MamE and show that its behavior is consistent with the previously proposed checkpoint model for biomineralization.


HtrA protease; MamE; bacteria; biomineralization; iron; magnetite; magnetosome; magnetotactic bacteria; metal; serine protease

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