Design and characterization of a chimeric ferritin with enhanced iron loading and transverse NMR relaxation rate.
This paper describes the design and characterization of a novel ferritin chimera. The iron storage protein ferritin forms a paramagnetic ferrihydrite core. This biomineral, when placed in a magnetic field, can decrease the transverse NMR relaxation times (T (2) and T (2)*) of nearby mobile water protons. Ferritin nucleic acid constructs have recently been studied as "probeless" magnetic resonance imaging (MRI) reporters. Following reporter expression, ferritin sequesters endogenous iron and imparts hypointensity to T (2)- and T (2)*-weighted images in an amount proportional to the ferritin iron load. Wild-type ferritin consists of various ratios of heavy H and light L subunits, and their ratio affects ferritin's stability and iron storage capacity. We report a novel chimeric ferritin with a fixed subunit stoichiometry obtained by fusion of the L and the H subunits (L*H and H*L) using a flexible linker. We characterize these supramolecular ferritins expressed in human cells, including their iron loading characteristics, hydrodynamic size, subcellular localization, and effect on solvent water T (2) relaxation rate. Interestingly, we found that the L*H chimera exhibits a significantly enhanced iron loading ability and T (2) relaxation compared to wild-type ferritin. We suggest that the L*H chimera may be useful as a sensitive MRI reporter molecule.
Iordanova
Bistra
B
Department of Biological Sciences, Carnegie Mellon University, 4400 Fifth Avenue, Pittsburgh, PA 15213, USA.
Robison
Clinton S
CS
Ahrens
Eric T
ET
D000595:Amino Acid Sequence; D000818:Animals; D002460:Cell Line; D005293:Ferritins / Q000737:chemistry* / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism*; D006801:Humans; D007501:Iron / Q000378:metabolism*; D008279:Magnetic Resonance Imaging; D008969:Molecular Sequence Data; D019906:Nuclear Magnetic Resonance, Biomolecular; D011489:Protein Denaturation; D015202:Protein Engineering / Q000379:methods*; D011993:Recombinant Fusion Proteins / Q000737:chemistry* / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism*
D011993:Recombinant Fusion Proteins; D005293:Ferritins; D007501:Iron
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