Journal
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
Volume 106, Issue 42, Pages 17751-17756Publisher
NATL ACAD SCIENCES
DOI: 10.1073/pnas.0909888106
Keywords
fast water dynamics; vibrational linear-chain exciton; 2-dimensional infrared spectroscopy
Categories
Funding
- National Institutes of Health [GM76201, GM12592, P01 RR01348]
- Alzheimer's Association
- National Science Foundation-Chemistry
- National Science Foundation Chemistry Research Instrumentation and Facilities Program [Chemistry-0131132]
- Direct For Mathematical & Physical Scien
- Division Of Chemistry [0809752] Funding Source: National Science Foundation
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The motion of water molecules close to amide groups causes their vibrational frequencies to vary rapidly in time. These variations are uniquely sensed by 2-dimensional infrared spectroscopy (2D IR). Here, it is proposed from 2-dimensional experiments on fibrils of amyloid beta(A beta)40 that there are water molecules in the fibrils. The spatial locations of the water (D2O) were inferred from the responses of 18 amide modes of A beta 40 labeled with C-13 = O-18. Fast frequency variations were found for residues L17 and V18 and for the apposed residues L34 and V36, suggesting cavities or channels containing mobile water molecules can form between the 2 sheets. Spectroscopic analysis showed that there are 1.2 water molecules per strand in the fibrils. The C-13 = O-18 substitution of 1 residue per strand creates a linear array of isotopologs along the fibril axis that manifests clearly identifiable vibrational transitions. Here, it is shown from the distributions of amide-I' vibrational frequencies that the regularity of these chains is strongly residue dependent and in most cases the distorted regions are also those associated with the putative mobile water molecules. It is proposed that A beta 40 fibrils contain structurally significant mobile water molecules within the intersheet region.
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