Developing Magnetic Resonance Reporter Gene Imaging: Essential Magnetosome Proteins Interact in Mammalian Cells

To detect cellular activities deep within the body using magnetic resonance (MR) platforms, magnetosomes are the ideal model of genetically-encoded nanoparticles. These organelle-like structures produced by magnetotactic bacteria (MTB) store iron biominerals in membrane-bound vesicles and are highly regulated by approximately 30 genes. To translate this technology into a gene-based iron contrast agent in mammalian cells [1], [2], we are introducing essential membrane-associated magnetosome (mam) genes mamI, mamL, mamB, and mamE into the human melanoma cell line MDA-MB-435 using fluorescent fusion protein vectors. While the expression of enhanced green fluorescent protein (EGFP)-MamI alone resulted in a net-like fluorescence pattern, individual expression of red fluorescent Tomato-MamL, Tomato-MamB, or Tomato-MamE all resulted in a mobile, punctate fluorescence pattern. Coexpression of MamL+I resulted in co-localization of both proteins in a mobile, punctate pattern. Here we report the transient expression of three magnetosome proteins (MamL+I+B or MamL+I+E) in mammalian cells, which results in the co-localization and interaction of all three proteins in a mobile, punctate pattern. These results further support interactions between essential magnetosome proteins in the mammalian intracellular compartment and the co-localization required to form a rudimentary magnetosome-like particle.