| Summary: | Recent findings have sparked great interest in the putative magnetic receptor protein MagR. However, in vivo experiments have revealed no magnetic moment of MagR at room temperature. Nevertheless, the interaction of MagR and MagR fusion proteins with silica-coated magnetite beads have proven useful for protein purification. In this study, we recombinantly produced two different MagR proteins in <i>Escherichia coli</i> BL21(DE3) to (1) expand earlier protein purification studies, (2) test if MagR can magnetize whole <i>E. coli</i> cells once it is expressed to a high cytosolic, soluble titer, and (3) investigate the MagR-expressing <i>E. coli</i> cells’ magnetic properties at low temperatures. Our results show that MagR induces no measurable, permanent magnetic moment in cells at low temperatures, indicating no usability for cell magnetization. Furthermore, we show the limited usability for magnetic bead-based protein purification, thus closing the current knowledge gap between theoretical considerations and empirical data on the MagR protein.
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