STRUCTURE AND FUNCTION ANALYSIS OF MAMC, A MAGNETITE-ASSOCIATED PROTEIN FROM MAGNETOTACTIC BACTERIA

The biomineralization process can be found in all kingdoms of life. It was shown that this process is under strict biological control, which involves proteins. Magnetotactic bacteria (MTB), a model system for studying biomineralization, can navigate through the Earth’s magnetic field via the synthesis of organelles called "magnetosomes". This organelle contains a magnetic nanoparticle of magnetite (Fe₃O₄) or greigite (Fe₃S₄) surrounded by a lipid membrane. It was shown that the magnetosome membrane contains a specific set of proteins that are thought to direct the biomineralization of magnetite crystals. One of the proteins involved in the formation of magnetite crystals is an integral membrane protein called MamC, a small protein (~12kDa) with two transmemebrane helices. In order to understand its function, we attached its magnetosomal loop (located between H1 to H2, which is predicted to interact with the magnetite crystal) to the C-terminal of MBP (maltose-binding protein). By using X-ray crystallography, we determined the MBP-MamC-loop structure from magnetotactic bacteria to a resolution of 2.8 Å. It has also been shown that it can interact with the magnetite particle using isothermal titration calorimetry (ITC) and affects magnetite crystal size and shape during iron precipitation in vitro. Based on these results, we identified a specific, negatively charged patch that is highly conserved among other MamC-homologous structure models. This patch may be important for the process of magnetite biomineralization and affect its size and shape. Therefore, the MamC loop could be used as an anchor between the magnetite particle and any desired, appropriate protein.