P-sheet content

There has been some discussion as to whether CD can distinguish parallel from antiparallel p sheets. As stable, well-defined model compounds are lacking, the spectra available have been derived from secondary structure deconvolutions (see below). Overall, the ability of CD to provide adequate estimates of both parallel and antiparallel p sheet contents is still an ongoing question. Johnson and co-workers were the first to derive basis spectra which corresponded to both parallel and antiparallel p sheet structures in globular proteins using the singular value deconvolution method [11, 12, 51-53], However, the basis spectra were significantly different from spectra reported for model sleet structures. Recently, Perczel et al. [54] employed another approach, convex curve analysis, to obtain improved p sheet baas spectra. The major improvement was to include more p sheet proteins into the data base. 

After adsorption one side of the protein molecule is oriented towards the sorbent surface, turned away from the aqueous solution. As a consequence, hydrophobic parts of the protein that are buried in the interior of the dissolved molecule may become exposed to the sorbent surface where they are still shielded from contact with water. Because hydrophobic interaction between apolar amino acid residues in the protein s interior support the formation of secondary structures as a-helices and P-sheets, a reduction of this interaction destabilizes such structures. Breakdown of the a-helices and/or P-sheets content is, indeed, expected to occur if peptide units released from these ordered structures can form hydrogen bonds with the sorbent surface. This is the case for polar surfaces such as oxides, e.g. silica and metal oxides, and with sorbent retaining residual water at their surfaces. Then the decrease in ordered secondary structures leads to an increased conformational entropy of the protein. This may favour the protein adsorption process considerably.13 It may be understood that proteins having an intrinsically low structural stability are more prone to undergo adsorption-induced structural changes. 

These features are characteristic of peptide random coil and p-sheet structures, and the magnitude of the positive ellipticity band revealed a significant difference in p-sheet contents between the two toxins. The secondary structures of the two toxins were found to be disrupted by the addition of 5.2 M guanidine hydrochloride at pH 7.4, since the spectra changed to a pattern typical of predominantly random coil structure. It was concluded that co-[d-Ser ]Aga-TK has a significantly higher p-sheet content than co-[l-Ser 6]Aga XK under neutral conditions. 

Table I Estimation of a-helix and p-sheet content in P-lactoglobulin using Brahms method as a function of ethanol concentration...

Protein secondary structure of CaLB in ILs was also studied by FTIR spectra. The IR bands at 1,650 and 1,658 cm" were due to a helix and at 1,620 and 1,640 cm" were because of p sheet content of the protein [47]. Protein secondary structure was undisrupted in [MTEOElMJCCHjCOO] and [MTEOTEAm][CH3COO], but in [EM1M][CH3C00] and [BMlM][HCOO], secondary structure was significantly changed as indicated by the altered band positions and intensities. IR spectra of... 

The normal form of the prion protein has a higher a-helix content compared to the p-sheet content. The abnormal one has an increased p-sheet content. 

Amyloid deposits are fibrous protein structures of high P-sheet content that are identified microscopically from their staining characteristics, giving a green birefringence when stained with the dye Congo red. 

The fit of the CD spectra reveals a helix content of approximately 90%. Although we could not quantify the p-sheet content in absolute numbers, addition of the anionic surfactant sodium dodecyl sulfate (SDS) caused the p-sheet content to increase with... 

The normal, cellular prion protein (PrP ) is converted into disease-causing prion (Prpsc) pj-oteins through a posttranslational process. After conversion, PrP loses some a-helical content, while PrP acquires a high p-sheet content. 

Secondary structure content was calculated by integrating the area between 1624 and 1628 cm (P-sheet content) and 1654 and 1658 cm (a-helical content), divided by the area under the amide I band (1600-1700 cm ), using a baseline from 1480-1715 cm ... 

In all images, the p-sheet content was slightly higher near the cell membranes and extracellular matrix. For the control animals (Figure 11.8A, left columns), the SFTIRM images appeared similar at each time point, indicating no... 

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