Study of Al3+ Binding and Conformational Properties of the Alanine-Substituted C-Terminal Domain of the NF-M Protein and Its Relevance to Alzheimer's Disease

Z. M. Shen, A. Perczel, G. D. Fasman, M. Hollósi, I. Nagypál

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Abstract

NF-M13 [H-(Lys-Ser-Pro-Val-Pro-Lys-Ser-Pro-Val-Glu-Glu-Lys-Gly)-OH], NF-M17 [H- (Glu-Glu-Lys-Gly-Lys-Ser-Pro-Val-Pro-Lys-Ser-Pro-Val-Glu-Glu-Lys-Gly)-OH], and their phosphorylated derivatives, representing the C-terminal phosphorylation domain of the neurofllament protein midsize subunit, have four possible binding sites for metal ions: the COO group of glutamate, the OH group of the serine residue, the PO3H group of phosphoserine (when present), and the COO at the terminus of the peptide chain. The CD titration of the phosphorylated neurofilament fragments with Al3+ and Ca2+ yielded a significant conformational change that resulted in conformations containing high β-pleated-sheet contents, which precipitate on standing (intermolecular complex). Al3+ binding to the unphosphorylated NF-M13 and NF-M17 did not exhibit this behavior. Several alanine analogues of the parent NF-M17 peptide were synthesized in order to determine the relationship between metal ions and possible binding sites. CD titration of analogues with Ca2+ indicated that the critical residues of NF-M17 for Ca2+-induced conformational changes, from random to β-pleated sheet, are the N-terminal serine or both phosphorylated serines. Al3+-induced conformational changes suggest that the critical sites of NF-M17 yielding the β-pleated-sheet structure are the four glutamates or phosphorylated serines, especially the C-terminal SerP. On the basis of the titration data, it is very likely that analogues with a serine in position 11 form a stable intramolecular complex with Al3+ that, however, does not result in the adoption of the β-conformation. Back-titration with citric acid fails to reverse the Al3+-induced conformational changes of the phosphorylated peptides. The above results, especially the possible formation of intramolecular and intermolecular Al3+ complexes, may have relevance to the molecular mechanism, through which the neurotoxin Al3+ gives rise to the formation of neurofilament tangles.

Original languageEnglish
Pages (from-to)9627-9636
Number of pages10
JournalBiochemistry
Volume33
Issue number32
DOIs
Publication statusPublished - Aug 1 1994

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ASJC Scopus subject areas

  • Biochemistry

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