PT - JOURNAL ARTICLE AU - David M. Hershey AU - Patrick J. Browne AU - Anthony T. Iavarone AU - Joan Teyra AU - Eun H. Lee AU - Sachdev S. Sidhu AU - Arash Komeili TI - Magnetite biomineralization in <em>Magnetospirillum magneticum</em> is regulated by a switch-like behavior in the HtrA protease MamE AID - 10.1101/047555 DP - 2016 Jan 01 TA - bioRxiv PG - 047555 4099 - http://biorxiv.org/content/early/2016/04/07/047555.short 4100 - http://biorxiv.org/content/early/2016/04/07/047555.full AB - Magnetotactic bacteria are aquatic organisms that produce subcellular magnetic crystals in order to orient in the earth’s geomagnetic field. The genetic basis for this process has been dissected in the model magnetotactic bacterium Magnetospirillum magneticum AMB-1, leading to the identification of biomineralization genes that control the formation and growth of magnetite crystals. One such factor, MamE, is a predicted member of the HtrA family of serine proteases, a widespread enzyme family that plays important roles in protein turnover and quality control. MamE was recently shown to promote the proteolytic processing of itself and two other biomineralization factors in vivo. Here, we have studied MamE-dependent proteolysis in detail. We 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 auto-proteolysis can be stimulated with exogenous substrates or peptides that bind to either of its PDZ domains. A constitutively active form of the protease causes biomineralization defects, showing that proper regulation of its activity is required during biomineralization in vivo. Our results demonstrate for the first time that MamE is a bonafide HtrA protease and that its activity is consistent with the previously proposed checkpoint model for biomineralization.