Unraveling of the E-helices and Disruption of 4-Fold Pores Are
Associated with Iron Mishandling in a Mutant Ferritin Causing
Neurodegeneration |
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Authors: | Martin A Baraibar Barry B Muhoberac Holly J Garringer Thomas D Hurley Ruben Vidal |
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Institution: | From the ‡Departments of Pathology and Laboratory Medicine and ;¶Biochemistry and Molecular Biology, Indiana University School of Medicine and ;the §Department of Chemistry and Chemical Biology, Indiana University-Purdue University Indianapolis, Indianapolis, Indiana 46202 |
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Abstract: | Mutations in the coding sequence of the ferritin light chain (FTL) gene cause a
neurodegenerative disease known as neuroferritinopathy or hereditary
ferritinopathy, which is characterized by the presence of intracellular
inclusion bodies containing the mutant FTL polypeptide and by abnormal
accumulation of iron in the brain. Here, we describe the x-ray crystallographic
structure and report functional studies of ferritin homopolymers formed from the
mutant FTL polypeptide p.Phe167SerfsX26, which has a C terminus that is altered
in amino acid sequence and length. The structure was determined and refined to
2.85 Å resolution and was very similar to the wild type between
residues Ile-5 and Arg-154. However, instead of the E-helices normally present
in wild type ferritin, the C-terminal sequences of all 24 mutant subunits showed
substantial amounts of disorder, leading to multiple C-terminal polypeptide
conformations and a large disruption of the normally tiny 4-fold axis pores.
Functional studies underscored the importance of the mutant C-terminal sequence
in iron-induced precipitation and revealed iron mishandling by soluble mutant
FTL homopolymers in that only wild type incorporated iron when in direct
competition in solution with mutant ferritin. Even without competition, the
amount of iron incorporation over the first few minutes differed severalfold.
Our data suggest that disruption at the 4-fold pores may lead to direct iron
mishandling through attenuated iron incorporation by the soluble form of mutant
ferritin and that the disordered C-terminal polypeptides may play a major role
in iron-induced precipitation and formation of ferritin inclusion bodies in
hereditary ferritinopathy. |
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Keywords: | Diseases/Genetic Diseases/Neurodegeneration Metals/Iron Methods/X-ray Crystallography Protein/Structure Ferritin Ferritinopathy |
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