The role of two Htra/DegP family proteases, MamE and MamO, in protein sorting and biomineralization in Magnetospirillum magneticum str AMB-1

Magnetotactic bacteria (MTB) are a diverse group of bacteria capable of synthesizing magnetosomes, membrane-bound prokaryotic organelles that biomineralize magnetic minerals. Magnetosomes allow cells to align passively with geomagnetic field lines. This is thought to facilitate a bacterium's search for favorable environments, a process referred to as magnetotaxis. To execute biomineralization, a specific set of proteins needs to be localized to the magnetosomes. I have taken both a candidate and a global approach to understanding how these magnetosome proteins (MPs) are sorted to the magnetosome.;In a global approach I attempted to identify magnetosome sorting signals by assaying magnetosome localization of N-terminal truncations of MPs. To carry out this approach I unsuccessfully attempted to optimize magnetosome purification protocols to separate inner membrane proteins from magnetosome membrane proteins.;In the more successful candidate approach, I show that the HtrA/DegP family protease MamE is essential for localization of several soluble, as well as membrane bound MPs. Using site-directed mutagenesis, I show that MamE's role in protein sorting is independent of its protease activity, but that protease activity is essential for a novel 20nm crystal size transition step. Site-directed mutagenesis also revealed that the protease activity of a second HtrA/DegP family protease, MamO, is essential for biomineralization. Furthermore, these studies suggest that MamE and MamO's additional functional domains, not usually found in HtrA/DegP family proteases, are required for magnetosome formation. Lastly, this work highlights the step-wise assembly of magnetosomes, illustrates that several levels of control underlie magnetosome formation, and proposes that by modulating MamE's protease activity, cells could potentially exert control over their degree of magnetism and thus magnetotaxis.