Anti-parallel chain /?-sheet

In a further exploration of the relationship between dye structure and wet fastness on silk, four novel monoazo J acid derivatives (3.169 X = Xx to X4), including 3.168 (X = X2) made from 2-aminobenzophenone, were synthesised. Silk was dyed at pH 4 and 85 °C and the dyeings tested for fastness to washing, perspiration and dry cleaning. The highest allround fastness was shown by the 4 aminobenzophenone derivative (X = X4), a structure that resembles the anti-parallel pleated sheet arrangement of polypeptide chains in silk [183]. 

Figure 4.7 (a) Parallel and (b) anti-parallel (3-sheets showing hydrogen bonds, but omitting side chains (from Voet and Voet, 2004) (c) parallel and (d) anti-parallel 3-sheets illustrating the pleated nature of the sheet. (From Branden and Tooze, 1991. Reproduced by permission of Garland Publishing, Inc.)... 

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.

Native monellin consists of two polypeptide chains, a 45-residue A-chain and a 50-residue B-chain, linked by non-covalent interactions. At neutral pH, it is fairly resistant to heat denaturation with a higher than 80 °C. The crystal structure of native monellin shows a tertiary structure comprising an anti-parallel /1-sheet with five strands and an a-helix. H NMR spectroscopy and hydrogen exchange methods have been used to characterize the alcohol-denaturated state of monellin in order to understand how its secondary structure depends on environmental conditions. " Structural and dynamic studies by NMR have been carried out in order to compare native monellin and a non-sweet analogue in which Asp was replaced by Abu . The three-dimensional structures of the two proteins are found to be very... 

There are two stable arrangements of nearly completely extended polypeptide chains forming hydrogen bonds with neighboring chains.114 They are the parallel-chain pleated sheet (Fig. 12-19) and the anti-parallel-chain pleated sheet (Fig. 12-20). The identity distance in the direction of the chains is found to be different for the two structures when the requirement that the N—H---0 bonds be linear is imposed ... 

P structure is the structure where the polypeptide chain is elongated. The structure can be the type where all the molecular chain run in the same direction and form a parallel pleated sheet or the type where the molecular chain run in the alternate direction and form anti parallel chain pleated sheet. In the case of P-structure, there are three important features, namely the period that is repeating period of the polypeptide chain, the spacing of the molecular chain in the sheet and the distance between the sheets [76]. 

All a subunits have a y -sandwidi structure (Fig. 3.3 a) formed by two five-anti-parallel /9-sheets with topology S8, SI, S2, S9 and SIO in the upper /9-sheet and S7, S6, S5, S4 and S3 in the lower /9-sheet. The sandwich structure is surrounded by helical layers comprising helices HI and H2 on one side and H3, H4 and H5 on the other, as seen in T. acidophilum and yeast. In every a subunit, the HO helix is found on the N-terminal side of SI. All /9 subunits of the bovine proteasome, like those in T. acidophilum and yeast, exhibit a /9-sandwich structure (Fig. 3.3 b) similar to that of the a subunits, consisting of strands SI to SIO. The polypeptide chain of the /9 subunits starts with strand SI the absence of helix HO provides access to the interior of /9-sandwich. The bovine /9-type subunits exhibit structural... 

FIGURE 10-7 Pleated sheet structures proposed for /8-keratin, (a) The parallel-chain pleated sheet, (b) The anti parallel-chain pleated sheet. [From Pauling and Corey, Proc. NatL Acad. Sci. U.S. 37, 729-40 (1951).]... 

Silk is a fibrous protein produced by several insect species. Commercially, silk is produced from the cocoon stage larvae of the moth caterpillar Bombyx mori, as it has been, in China, for some 4500 years. A single cocoon produces a continuous thread up to 1 km in length, and the protein fibroin contains large amounts of glycine, alanine, tyrosine, proline and serine The peptide chains are arranged in anti-parallel P-sheets which make up the hierarchical structure of the crystalline silk fibres. A number of spiders also produce silk webs, although the fibroin structure is rather different to that from silk worms. 

As with other natural fibres, silk has a hierarchical microstructure - about five anti-parallel (f-sheets, each with around 12 chains, aggregate to form parallel, crystalline microfibrils (approximately 10 nm in diameter), bundles of which make up fibrillar elements (roughly 1 p,m across), which in turn associate to comprise the individual fibroin filaments (7-12 xm) at each level of organisation, the ordered elements are embedded within amorphous matrices derived from the non-crystalline components. Once again, then, the behaviour of the structural composite can be understood in terms of the semi-crystalline array of its component parts. 

Figure 1.8 Amino add residue side-chain interactions further restrict free rotation in peptide or polypeptide backbone. Rotational possibilities are defined by allowed values of dihedral angle 4> subtended about N—Co, bond and V subtended about Co,—C(0) bond (left). Theoretically allowed angles are shown in Ramachandran plot (right) together with positions of actual angles found in real protein secondary structures a right-handed a-helix ai. left-handed a-helix parallel/S-sheet f anti-parallel 8-sheet C collagen, Pn helix (see later). (Ramachandran plot from Voet, Voet Pratt, 1999 [Wiley], Fig. 6-6).

Figure 1.19 Depiction of /3-sheet structures from indicated proteins, (a) Schematic Display Structure (see Section 1.2.5 each flat arrow is a /3-strand with arrow head equal to C-terminus of each strand cylinders are a-helices remainder represent loops and turns) of anti-parallel /3-sheet segment of carbonic anhydrase I (human erythrocyte) (pdb 2cab), atoms and bonds of amino acid side-chains are rendered in ball and stick representation with carbon (grey), nitrogen (blue) and oxygen (red) (b) Schematic Display Structure of parallel /3-sheet segment of triose phosphate isomerase (chicken muscle) (pdb Itim), atoms and bonds of side-chains are rendered as in (a).

Monellin, an intensively sweet protein from the West African berries Dioscoreophyllum cumminsii. On a weight basis, monellin is several thousand times more potent in sweetness than sucrose. It consists of two non-covalently associated polypeptide chains, A and B, with 44 and 50 residues, respectively. According to the X-ray crystal structure, the natural protein consists of an anti-parallel /S-sheet with five strands and an a-hdix. Single-chain moneUin (SCM), an engineered 94 aa polypeptide, has been proven to be as sweet as the native two-chain molecule, and is more stable in both high-temperature and acidic environments compared to the native monellin [T. Mizukoshi et al., FEBS Lett. 1997, 413, 409 ... 

Figure 9.6.8 Arrangement of hydrogen bonds in the anti-parallel chain pleated sheet P-structure described by Pauling and Corey. ...

The different production history and composition in terms of amino acid percentages found in silk reflects into a different X-ray pattern, described by an arrangement of the chains in what is termed as anti-parallel P-sheet and shown in Figure 9.6.8. The same configuration, which is stable for silk fibroin, is also achieved metastably by oc-keratins when stretched in a wet environment. ... 

With this constraint data, one then resorts to compnter minimization of allowed conformations of the 18 amino acid chain and the resnlts are show in Figure 7.7. Clearly much flexibUity exists in certain bonds of the molecule, but other parts arc very well defined by an anti-parallel /3-sheet with a hairpin turn. There are 17 structures that fit the constraints and all are shown in the figure. 

Ferrocene has a suitable distance between Cp (cyclopentadienyl) ligands for the spacer of anti-parallel 3-sheet (Fig. 3.36(a)). The freely rotatable bond is appropriate for adjusting the distance between two peptide chains In this section, the combination of non-natural amino acid with natural peptide is described. 

Figure 9. Drawing representing the anti-parallel-chain pleated-sheet structure.

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