Kim Yung Sam, Liu Liu, Axelsen Paul H, Hochstrasser Robin M
Department of Chemistry, University of Pennsylvania, Philadelphia, PA 19104-6323, USA.
Proc Natl Acad Sci U S A. 2008 Jun 3;105(22):7720-5. doi: 10.1073/pnas.0802993105. Epub 2008 May 22.
The 2D IR spectra of the amide-I vibrations of amyloid fibrils from Abeta40 were obtained. The matured fibrils formed from strands having isotopic substitution by (13)C (18)O at Gly-38, Gly-33, Gly-29, or Ala-21 show vibrational exciton spectra having reduced dimensionality. Indeed, linear chain excitons of amide units are seen, for which the interamide vibrational coupling is measured in fibrils grown from 50% and 5% mixtures of labeled and unlabeled strands. The data prove that the 1D excitons are formed from parallel in-register sheets. The coupling constants show that for each of the indicated residues the amide carbonyls in the chains are separated by 0.5 +/- 0.05 nm. The isotope replacement of Gly-25 does not reveal linear excitons, consistent with the region of the strand having a different structure distribution. The vibrational frequencies of the amide-I modes, freed from effects of amide vibrational excitation exchange by 5% dilution experiments, point to there being a component of an electric field along the fibril axis that increases through the sequence Gly-38, Gly-33, Gly-29. The field is dominated by side chains of neighboring residues.
获得了β淀粉样蛋白40（Aβ40）淀粉样纤维酰胺-I振动的二维红外光谱。由在Gly-38、Gly-33、Gly-29或Ala-21处具有（13）C（18）O同位素取代的链形成的成熟纤维显示出维度降低的振动激子光谱。实际上，可以看到酰胺单元的线性链激子，在由标记链和未标记链的50%和5%混合物生长的纤维中测量了其酰胺间振动耦合。数据证明一维激子由平行的共线片层形成。耦合常数表明，对于每个指定的残基，链中的酰胺羰基间距为0.5±0.05nm。Gly-25的同位素取代未显示线性激子，这与链的该区域具有不同的结构分布一致。通过5%稀释实验消除酰胺振动激发交换影响的酰胺-I模式的振动频率表明，沿纤维轴存在一个电场分量，该分量在Gly-38、Gly-33、Gly-29序列中增加。该电场由相邻残基的侧链主导。
