Protein P-sheets

Domains in which the secondary structure is almost exclusively P-sheets tend to contain two sheets packed face to face. There are two major classes those in which the strands are almost parallel and those in which the strands are almost perpendicular. The strands 

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Fig. 9. A de novo designed P sheet protein, betabellin, formed by the dimerization of two identical four-stranded -sheets and a disulfide linking the two sheets. This model is for betabeUins 9 and later progenies the earher betabeUins contained a two-armed cross-linker connecting the sheets (51).

Wilkes et al (22.23) coupled calorimetric, dynamic-mechanical and x-ray diffraction techniques to demonstrate crystallization of the lipids was completely reversible in neonatal rat stratum corneum, and only partially reversible in human stratum corneum. Melting regions near 40°C and from 70 to 90°C corresponded to the thermal transitions noted in the calorimetric studies for both species. The crystalline nature of the lipids did not appear to be dependent on the presence of water. X-ray diffraction and infrared spectroscopy studies (23.28-34) have also shown a to p conformational changes occurred in keratin and stratum corneum protein components with hydration or exposure to increased temperatures. Oertel (28) has reported pretreatment with dimethylsulfox-ide, hexylmethylsulfoxide and decylmethylsulfoxide resulted in the formation of p-sheet protein conformations in vitro in human... 

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. 

Richardson JS, Richardson DC (2002) Natural p-sheet proteins use negative design to avoid edge-to-edge aggregation. Proc Natl Acad Sci USA 99 2754-2759... 

Present study deals with specific aspects of development of hybrid proteins capable to create p-sheeted protein fibrils and integration of the fibrils with solid surfaces. Our study aims to define the most essential conditions and parameters on which the arrangement of the complex object on the solids depends. Morphology,... 

The prefactor, P, depends on the electronic coupling of donor and acceptor with the bridging orbitals. A correlation between p (cf. Eq. 3) and Ec (Eq. 4) is easily demonstrated An individual strand of a p-sheet protein defines a linear tunneling pathway along the peptide, spanning a distance (r — ro) of 0.34 nm per residue (three covalent bonds). Thus, inserting a p value of 10 nm in Eq. 3, the decay factor, Ec of Eq. 4 becomes 0.6 per covalent bond. 

Fig. 16J. The relationship between the percentage sequence differences and the rms distance differences between topologically equivalent C positions in optimally superposed pairs of homologous protein three-dimensional structures (taken from [2]). The are for all equivalent amino acids and the + are for those whose side chains contribute to the solvent inaccessible core. The lines in a are the best unweighted least-squares fits of quadratic equations for the following sets of points TA is for all points TI is for all + points BA and BI are for P sheet proteins while AA and AI are for those with a helices, b shows data for P sheet proteins and c for a helical proteins. Lines linking and + points for individual proteins are plotted in b and c...

Figure 3. Deconvoluted aqueous solution spectra of P-sheet proteins in the Amide I and Amide II spectral regions. Top IgG bottom concanavalin A.

Insects and arachnoids produce well-known amyloids. Silk and spider webs, like P-keratin, also differ from amyloids in being fibrous P-sheet proteins composed of peptide strands that are parallel, rather than perpendicular, to the direction of the fibril axis. For the process of silk formation by spiders, it has been proposed that fibrils in the silk gland have an initial cross-P structure (Kenney et al. 2002 Table 3) that, when stretched, assume parallel P-structures. However, X-ray diffraction for a peptide derived from the central domain of the A class of chorion proteins, derived frovaAntheraea polyphemus eggshells, displayed P-sheets perpendicular to the fibril axis, the same cross-P structure that occurs in amyloid proteins (Iconomidou et al. 2000 Table 3). The stability and strength of the amyloid fibres provides mechanical and biological protection for the oocyte and developing embryo from a variety of environmental and predatory hazards. 

Parallel P-sheet proteins. The most common arrangement in this class contains four strands for each sheet to form the natural twist. However, the directions of the strands are not all equivalent and the connectivities of the strands are different, such as prealbumin (e.g. transthyretin, Figure 5.10C) in a Greek key topology. 

Orthogonal P-sheet proteins. An alternative way of packing two P-sheets together is with the strands in the two sheets almost perpendicular in a trefoil superfold. Each domain of the serine proteases (e.g. trypsin. Figure 5.10D) shows this arrangement. 

Other P-sheet proteins. Influenza neuraminidase contains an unusual P-sheet propeUer-like structure (Figure 5.10E). Ascorbate oxidase and galactose oxidase are laige P-sheet proteins that contain parallel P-sheet domains in a jeUyroU- or sandwich-like structure. 

Eyles, S.J., Dresch, T, Gierasch, L.M., Kaltashov, I.A. (1999) Unfolding dynamics of a p-sheet protein studied by mass spectrometry. J Mass Spectrom, 34 (12), 1289-1295. 

Electron transfer in biological systems where the electron donor and acceptor are separated by a long molecular distance is encountered in very important processes such as photosynthesis and respiration [54]. As natural systems are not appropriate for such studies. Gray et al. have employed proteins chemically labeled with transition metal complexes to measure ET rates in metaUoproteins. In particular, they have shown that long-lived luminescent probes enabled a wider range of ET measurements than is possible with non-luminescent complexes [55]. The blue copper protein azurin is a convenient model for the study of ET in p-sheet proteins. 

B. D. Bursulaya and C. L. Brooks III, Folding free energy surface of a three-stranded p-sheet protein. J. Am. Chem. Soc. 121, 9947-9951 (1999). 

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