Protein parallel 3 sheets

The /(-helix is a well-authenticated fold, having been observed in more than 20 crystal structures, mostly of secreted bacterial proteins (Jenkins and Pickersgill, 2001 Yoder and Jurnak, 1995 see also Kajava and Steven, this volume). In a /(-helix, the polypeptide chain winds around the molecular axis, each coil consisting of three short /(-strands with connecting turns (Fig. 11). Corresponding strands in successive turns are stacked, generating narrow parallel /(-sheets that are aligned with the... 

Ghan,J. C., Oyler, N. A., Yau, W. M., and Tycko, R. (2005). Parallel //-sheets and polar zippers in amyloid fibrils formed by residues 10-39 of the yeast prion protein Ure2p. Biochemistry 44, 10669-10680. 

Figure 11.4 Pleated sheets of fibrous proteins. Parallel pleated sheets are composed of polypeptide chains which all have their N-terminal amino acid at the same end whereas anti-parallel pleated sheets involve polypeptide chains which are alternately reversed in direction. Both forms of sheet show a high degree of hydrogen bonding between the chains.

After a-helices, P-sheets are the most prominent secondary structure feature in globular proteins. However, the most widely used tool for secondary analysis, ultraviolet ECD, is so dominated by its sensitivity to the a-helix that, at best, it can only poorly characterize ( -sheet content. IR on the other hand has a good differential sensitivity to the p-sheet because of the large frequency shift ( 30 cm-1) from the helical band and because the extinction coefficient for model extended sheets is often higher than for other conformations. However, study of the p-sheet conformation with peptide models has long been hindered by their natural tendency to aggregate. Furthermore, no (or very few) peptide models of parallel sheets are available, to our knowledge. 

Other [3-Sheet Proteins. Influenza neuraminidase contains a very unusual [I-sheet propellor-like structure. Ascorbate oxidase (Figure 12. le) is a large / -sheet protein that contains parallel / -sheet domains, and interleukin-1/1 may be described as containing both a barrel and a propeller. 

Salemme FR, Weatherford DW (1981) Conformational and geometrical properties of / -sheets in proteins. I. Parallel -sheets. J Mol Biol 146 101-117 II. Antiparallel and mixed /1-sheets. J Mol Biol 146 119-141... 

The p Sheet Another type of secondary structure, the p sheet, consists of laterally packed p strands. Each p strand is a short (5- to 8-residue), nearly fully extended polypeptide segment. Hydrogen bonding between backbone atoms in adjacent p strands, within either the same polypeptide chain or between different polypeptide chains, forms a p sheet (Figure 3-4a). The planarity of the peptide bond forces a p sheet to be pleated hence this structure is also called a 3 pleated sheet, or simply a pleated sheet. Like a helices, p strands have a directionality defined by the orientation of the peptide bond. Therefore, in a pleated sheet, adjacent p strands can be oriented in the same (parallel) or opposite (antiparallel) directions with respect to each other. In both arrangements, the side chains project from both faces of the sheet (Figure 3-4b). In some proteins, p sheets form the floor of a binding pocket the hydrophobic core of other proteins contains multiple P sheets. 

The nomenclature first described by Adams et al. (10) and later extended by Hill et al. (IS) will be used in the description of this protein fragment (Fig. 4). The main structural elements of this domain are six strands of parallel sheet (y3A, fiB, pC, pD, fiE, and /3F) and four helices ( B, aC, aE, and alF). There are two helices on each side of the sheet. There is a gradual, left-handed twist, from one strand to the next. 

It has been proposed that native protdn molecules are made up of parallel sheets or layers of peptide chains (72, 73, 74, 75). It is reasonable to believe that these layers have the same hydrophilic-hydrophobic characteristics as do spread films. Thus in a native molecule containing two such layers of peptide chains, the outer faces of the molecule would be predominantly hydrophilic with a hydrophoWc sandwich in between. Dervichian, for example, has drawn an anal< between a soap micelle and a protein molecule as far as the arrangement of the hydrophilic and hydrophobic groups are concerned. Certainly, there is much evidence to substantiate such a picture. While most of this evidence is of an indirect nature, it is no less compelling. Without the layer structure of the native molecule as the guiding idea, the formation of protein spread monolayers is difficult to understand. 

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