Abstract
Amyloid fibril formation occurs in restricted environment, such as the interface between intercellular fluids and bio-membranes. Conformational interconversion from α-helix to β-structure does not progress in fluids; however, it can occur after sedimentary aggregation during amyloid fibril formation induced by heat treatment of hen egg white lysozyme (HEWL). Secondary structures of various proteins and denatured proteins titrated with 2,2,2-trifluoroethanol (TFE) were examined using their CD spectra. Gaussian peak/trough and singular value decompositions (SVD) showed that the spectral pattern of the α-helix comprised a sharp trough at wavelength 207 nm and a broad trough at 220 nm. Conversely, we distinguished two patterns for β-sheet—a spread barrel type, corresponding to ConA, and a tightly weaved type, corresponding to the soybean trypsin inhibitor. Herein, we confirmed that the spectral/conformational interconversion of the heat-treated HEWL was not observed in the dissolved fluid.
Highlights
Alzheimer’s dementia [1], Parkinson’s extrapyramidal disorders [2], Huntington’s chorea [3], type II diabetes [4], amyotrophic lateral scle rosis (ALS) [5], and other national-designated intractable cases are some of the examples of amyloid diseases; 40 types of human proteins asso ciated with such diseases have been identified until 2018 [6], the occurrence of which is caused by irregular aggregation and localization induced by steric changes [7]
Except for concanavalin A (ConA), the proportions of α-helical and β-sheet segments of selected proteins disagreed with the results of the curve-fitting with Woody’s straightforward basis set and the residual proportion retrieved from Protein Data Bank (PDB) entry records
The conformational interconversion pro gressed only in the precipitates. This comparative study showed that the (i) curve-fitting procedure with the linear combination of Woody’s straightforward basis set for their artificial α-helix, β-strand/sheet, and "random coil" segments, (ii) Gaussian peak/trough decomposition procedure, and (iii) singular value de compositions (SVD) proced ure were verified to distinguish the contributions of the secondary structures on the observed far-ultraviolet circular dichroism (CD) spectra of proteins
Summary
Alzheimer’s dementia [1], Parkinson’s extrapyramidal disorders [2], Huntington’s chorea [3], type II diabetes [4], amyotrophic lateral scle rosis (ALS) [5], and other national-designated intractable cases are some of the examples of amyloid diseases; 40 types of human proteins asso ciated with such diseases have been identified until 2018 [6], the occurrence of which is caused by irregular aggregation and localization induced by steric changes [7]. If the protein misfolding is achieved, the segment will be antecedently affected by the environmental conversion to enforce the conformational change [13] This scenario is essential for the formation of β-strand/ sheet structures [14]. Each amide moiety has one particular space orientation depend on the for mation of standard conformations by hydrogen bonds between main chain atoms, such as α-helices, β-strands/sheets, various turns, and disordered segments [22]. Bovine and human serum albumins (BSA and HSA, respectively) were examined as typical models predominantly comprising α-helices [25,26], whereas a legume lectin concanavalin A (ConA) was manipulated as the opposite example, comprising 14 β-strand components of antiparallel sheets in the diverse ligand-accessible barrel structure [27,28]. Their amino acid residual proportions, with which the α-helical, β-strand/sheet, and disordered segments of HEWL and other proteins, retrieved from Protein Data Bank (PDB) entries, appear in the caption of Fig. 1
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