Cellular distribution and motion of essential magnetosome proteins expressed in mammalian cells

Magnetosomes are organelle-like structures within magnetotactic bacteria that store iron biominerals in membrane-bound vesicles. In the bacteria, formation of these structures is highly regulated by approximately 30 genes which are conserved throughout different species. To compartmentalize iron in mammalian cells for magnetic resonance imaging using gene-based contrast, we are introducing key magnetosome proteins. We have previously expressed essential magnetosome genes mamI and mamL as fluorescent fusion proteins in the human melanoma cell line MDA-MB-435 and confirmed their co-localization and interaction. Here we investigate the expression of magnetosome genes mamB and mamE in MDA-MB-435 cells, using confocal fluorescence microscopy to observe expression patterns and to analyze particle mobility. Custom software was developed to characterize fluorescent particle trajectories. In mammalian cells, essential magnetosome proteins displayed different diffusive behaviours. However, all magnetosome proteins travelled at similar velocities when undergoing directed motion, suggesting that MamL, MamL+MamI, MamB, and MamE interact with similar mammalian mobile elements. These results confirm that localization and interaction of essential magnetosome proteins is tenable in the mammalian intracellular compartment.