Journal of Biological Chemistry
Volume 284, Issue 35, 28 August 2009, Pages 23580-23591
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Protein Structure and Folding
Amino Acid Position-specific Contributions to Amyloid β-Protein Oligomerization*

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Understanding the structural and assembly dynamics of the amyloid β-protein (Aβ) has direct relevance to the development of therapeutic agents for Alzheimer disease. To elucidate these dynamics, we combined scanning amino acid substitution with a method for quantitative determination of the Aβ oligomer frequency distribution, photo-induced cross-linking of unmodified proteins (PICUP), to perform “scanning PICUP.” Tyr, a reactive group in PICUP, was substituted at position 1, 10, 20, 30, or 40 (for Aβ40) or 42 (for Aβ42). The effects of these substitutions were probed using circular dichroism spectroscopy, thioflavin T binding, electron microscopy, PICUP, and mass spectrometry. All peptides displayed a random coil → α/β → β transition, but substitution-dependent alterations in assembly kinetics and conformer complexity were observed. Tyr1-substituted homologues of Aβ40 and Aβ42 assembled the slowest and yielded unusual patterns of oligomer bands in gel electrophoresis experiments, suggesting oligomer compaction had occurred. Consistent with this suggestion was the observation of relatively narrow [Tyr1]Aβ40 fibrils. Substitution of Aβ40 at the C terminus decreased the population conformational complexity and substantially extended the highest order of oligomers observed. This latter effect was observed in both Aβ40 and Aβ42 as the Tyr substitution position number increased. The ability of a single substitution (Tyr1) to alter Aβ assembly kinetics and the oligomer frequency distribution suggests that the N terminus is not a benign peptide segment, but rather that Aβ conformational dynamics and assembly are affected significantly by the competition between the N and C termini to form a stable complex with the central hydrophobic cluster.

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*

This work was supported, in whole or in part, by National Institutes of Health Grants AG018921, AG027818, and RR020004. This work was also supported by a Zenith Award from the Alzheimer's Association.

The on-line version of this article (available at http://www.jbc.org) contains supplemental Table S1 and Figs. S1 and S2.

1

Present address: School of Bioscience and Bioengineering, IIT Bombay, Powai, Mumbai 400076, India.

2

Present address: Dept. of Biochemistry and Molecular Pharmacology, University of Massachusetts Medical School, Worcester, MA 01655.