Sheet, / -, protein

Koch, I., Kaden, R, Selbig, J. Analysis of protein sheet topologies by graph theoretical methods. Prot Struc. Func. Genet. 12 314-323, 1992. 

Figure 19.7 Molecular correspondence of the inorganic-organic interface in the nacreous shell layer of Nautilus repertus. (a) Structural relationships between protein sheets, aragonite crystals and chitin fibres, (b) Possible complementarity of Ca binding. (From Mann et al., 1989. Reproduced with permission from John Wiley Sons., Inc.)...

In summary, the arthropod cuticle is not chitinous and can probably best be described as a plasticized, protein sheet, variously subdivided to give a laminar structure by (a) the addition of waxes at the outer surfaces and chitin in the inner parts, and (b) hardening due to impregnation with calcium salts or further polymerization with polyphenols, or both. 

Sothomvit, R., Olsen, C.W., McHugh, T.H., and Krochta, J.M. (2007). Tensile properties of compression-molded whey protein sheets Determination of molding condition and glycerol-content effects and comparison with solution-cast films. J. Food Eng. 78, 855-860. 

Fitting of Molecular Shapes. Planar surfaces, e.g., boardlike cellulose fibers, protein sheets, or disklike porphyrins, as well as concave-convex pairs, e.g., cyclodextrin and polymer fibers, tend to form molecular assemblies (Figs. 

Fig. 4.10. Schematic representation of the structural relationships between protein sheets, aragonite crystals, and chitin fibres in the nacreous layer of N. repertus ...

The S-layer of S. ureae ATCC 13881 has been reported to be an excellent biotemplate for fabrication of highly ordered metal cluster arrays. Pt was deposited onto the isolated protein sheets by first incubating the metal salt with the S-layer followed by a reducing step to obtain metallic Pt particles (Mertig et al., 1999). As a result, highly ordered nanocluster arrays were formed on the protein template reproducing its square symmetry. 

FIGURE 7.14 The architecture of protein sheets (drawn using SUAO.pdb). Dashed yellowish lines connecting red and blue parts on the left are H-bonds (the hydrogen atoms... 

Usually, compression molding is studied as a precursor of extrusion, to study the material machinability and to identify appropriate conditions for extrusion. In this study, the authors have shown that the mechanical properties of whey protein sheets molded by compression with 40-50% plasticizer were better than films produced by casting with 45% plasticizer. The authors also claim that extrusion is a quick process, requires little space and has a small number of production steps. ... 

Zhang X, Mungara P, Jane I Mechanical and thermal properties of extruded soy protein sheets. 

The major drawback of protein-based plastics, apart from keratin, is their sensitivity towards relative humidity. For example, it was reported that after being submerged in water for 20 h the soy protein sheets absorbed up to 180% water [56]. 

Figure 7.15 Plots of tan 8 versus temperature for DMA scans of extruded soy protein sheets at different moisture contents (reprinted from Polymer, 42(6), J. Zhang, P. Mungara and J. Jane, Mechanical and thermal properties of extruded soy protein sheets, 2569-2578. Copyright (2001), with permission from Elsevier) and amylose films plasticized with different glycerol contents (reprinted from Carbohydrate Polymers, 22(3), G. K. Moates, T. R. Noel, R. Parker and S, G. Ring, Dynamic mechanical and dielectric characterisation of amylose-glycerol films, 247-253. Copyright (2001), with permission from Elsevier.)...

Glass transitions of dry, unplasticized proteins are typically in the range of 120-250 °C depending on protein structure. For highly plasticized proteins, Tg can be well below ambient temperatures. For example, DSC of compression moulded soy protein sheets plasticized with 50-70 g ethylene glycol per 100 g soy protein revealed the Tg to be in the range of -90 to -70 °C. ... 

The structures now available at 5-8 A resolution allow differentiation of protein a-helices from double-helical regions of rRNA based on their structural characteristics some protein -sheets can also be seen. The structures of several individual ribosomal proteins have been solved by X-ray crystallography or nuclear magnetic resonance spectroscopy, and the X-ray data on the whole 508 particle have been correlated with the previously determined structures of individual proteins. As expected, the accumulated data fromlEM, cross-linking, and neutron diffraction helped to position these protein stmctures within the ribosome electron density and will continue to direct placement of proteins and specihc regions of rRNA. 

Zhang,)., Mungara, P.,and Jane,). (2001). Mechanical and thermal properties of extruded soy protein sheets. Polymer, 42(6), 2569-2578. 

Therefore, in all proteins, sheets have a tendency to form a right-handed twist, but the extent of the twist varies for each sheet. A schematic representation of carboxypeptidase, according to Richardson, shows the twist of a... 

Figure Bl.17.11. Reconstructed density of an a,p-tiibulin protein dimer as obtained from electron crystallography (Nogales etal 1997). Note the appearance of the p-sheets ((a), marked B) and the a-helices ((b), marked H) in the density. In particular the right-handed a-helix H6 is very clear. Pictures by courtesy of E Nogales and Academic Press.

Protems can be physisorbed or covalently attached to mica. Another method is to innnobilise and orient them by specific binding to receptor-fiinctionalized planar lipid bilayers supported on the mica sheets [15]. These surfaces are then brought into contact in an aqueous electrolyte solution, while the pH and the ionic strength are varied. Corresponding variations in the force-versus-distance curve allow conclusions about protein confomiation and interaction to be drawn [99]. The local electrostatic potential of protein-covered surfaces can hence be detemiined with an accuracy of 5 mV. 

Figure C3.2.6. Zones associated witlr the distinctive decay of electronic coupling tlrrough a-helical against p-sheet stmctures in proteins. Points shown refer to specific rates in mtlrenium-modified proteins aird in tire photosyntlretic reaction centre. From Gray H B aird Wiirkler J R 1996 Electron trairsfer in proteins A . Rev. Biochem. 65 537.

Proteins are biopolymers formed by one or more continuous chains of covalently linked amino acids. Hydrogen bonds between non-adjacent amino acids stabilize the so-called elements of secondary structure, a-helices and / —sheets. A number of secondary structure elements then assemble to form a compact unit with a specific fold, a so-called domain. Experience has shown that a number of folds seem to be preferred, maybe because they are especially suited to perform biological protein function. A complete protein may consist of one or more domains. 

Cohen F E, M J E Sternberg and W R Taylor 1982 Analysis and Prediction of the Paclung oi. i-E a iinst a /3-Sheet in the Tertiary Structure of Globular Proteins. Journal of AdoljcuLir E 156 821-862. 

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