Distinguishing islet amyloid polypeptide fibril structures with infrared isotope-label spectroscopy
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Abstract:
Here, we performed spectral simulations of the amide-I vibrational spectra for three proposed fibril structures of the human islet amyloid polypeptide, which is involved in type II diabetes. We modeled both the overall absorption and two-dimensional infrared spectra for these structures. We further analyzed the isotope-labeled spectra, including the variation between structures. The analysis suggests that the infrared spectra of the cryo-electron microscopy structure provide the best match with experimental data. We further simulated isotope-labeled dilution spectroscopy investigating the correlation between the predicted spectral peak shift and the coupling between the amide units. While this correlation works in most cases, failures were observed when the isotope-labeled spectra were broad compared to the coupling or exhibited structure. These findings will be useful in the quest for potential toxic fibril formation intermediates.Keywords:
Amyloid (mycology)
Two-dimensional infrared spectroscopy
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Mid-infrared spectroscopy has been applied to zeolite structural problems. The infrared spectrum in the region of 200 to 1300 cm-1 is a sensitive tool indicating structural features of zeolite frameworks. Preliminary interpretation suggests infrared specificity for zeolite structure type and group, and for structural subunits such as double rings and large pore openings. It is proposed that the major structural groups present in zeolites can be detected from their infrared pattern. This hypothesis is based on correlation of newly determined infrared spectra of synthetic zeolites with x-ray structure data for most of the known structural classes of zeolites. Other structural information obtained from infrared studies includes framework Si/Al composition, structural changes during thermal decomposition, and cation movement during dehydration and dehydroxylation.
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Two-dimensional infrared spectroscopy
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Two-dimensional infrared spectroscopy
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Preformed amyloid fibrils accelerate conformational changes of amyloid precursor proteins and result in rapid extension of amyloid fibrils in vitro. We injected various kinds of amyloid fibrils into mice with amyloidogenic apoAII gene ( Apoa2 C ). The most severe amyloid depositions were detected in the tissues of mice injected with mouse AApoAII(C) amyloid fibrils. Mild amyloid depositions were also detected in the tissues of mice that were injected with other types of fibrils, including synthetic peptides and recombinant proteins. However, no amyloid depositions were found in mice that were injected with non‐amyloid fibril proteins. These results demonstrated that a common structure of amyloid fibrils could serve as a seed for amyloid fibril formation in vivo.
Amyloid (mycology)
Amyloid disease
P3 peptide
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Characterization
Two-dimensional infrared spectroscopy
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The data presented show that infrared group frequencies are only applicable for specific spectra structure identification when the infrared spectrum of the unknown material is recorded in the same manner as that used to record the infrared spectra used to build the IR group-frequency data base. IR spectra recorded of compounds in different phases such as the liquid, solution, and vapor phase are useful in helping one to determine whether a compound exists in more than one rotational molecular configuration such as rotation of a CHCl 2 group about a C-C=O single bond in compounds of form CHCl 2 -C=O.
Carbonyl group
Base (topology)
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Two-dimensional infrared spectroscopy
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Cryoelectron microscopy (cryo-EM) has provided unprecedented insights into amyloid fibril structures, including those associated with disease. However, these structures represent the endpoints of long assembly processes, and their relationship to fibrils formed early in assembly is unknown. Consequently, whether different fibril architectures, with potentially different pathological properties, form during assembly remains unknown. Here, we used cryo-EM to determine structures of amyloid fibrils at different times during in vitro fibrillation of a disease-related variant of human islet amyloid polypeptide (IAPP-S20G). Strikingly, the fibrils formed in the lag, growth, and plateau phases have different structures, with new forms appearing and others disappearing as fibrillation proceeds. A time course with wild-type hIAPP also shows fibrils changing with time, suggesting that this is a general property of IAPP amyloid assembly. The observation of transiently populated fibril structures has implications for understanding amyloid assembly mechanisms with potential new insights into amyloid progression in disease.
Amyloid (mycology)
Fibrillation
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