Hydrogen bonds pleated sheet

Section 27 19 Two secondary structures of proteins are particularly prominent The pleated sheet is stabilized by hydrogen bonds between N—H and C=0 groups of adjacent chains The a helix is stabilized by hydrogen bonds within a single polypeptide chain... 

The crystal stmcture of PPT is pseudo-orthorhombic (essentially monoclinic) with a = 0.785/nm b = 0.515/nm c (fiber axis) = 1.28/nm and d = 90°. The molecules are arranged in parallel hydrogen-bonded sheets. There are two chains in a unit cell and the theoretical crystal density is 1.48 g/cm. The observed fiber density is 1.45 g/cm. An interesting property of the dry jet-wet spun fibers is the lateral crystalline order. Based on electron microscopy studies of peeled sections of Kevlar-49, the supramolecular stmcture consists of radially oriented crystaUites. The fiber contains a pleated stmcture along the fiber axis, with a periodicity of 500—600 nm. 

Fig. 2. Protein secondary stmcture (a) the right-handed a-helix, stabilized by intrasegmental hydrogen-bonding between the backbone CO of residue i and the NH of residue t + 4 along the polypeptide chain. Each turn of the helix requires 3.6 residues. Translation along the hehcal axis is 0.15 nm per residue, or 0.54 nm per turn and (b) the -pleated sheet where the polypeptide is in an extended conformation and backbone hydrogen-bonding occurs between residues on adjacent strands. Here, the backbone CO and NH atoms are in the plane of the page and the amino acid side chains extend from C ...

Figure 2.6 Parallel p sheet, (a) Schematic diagram showing the hydrogen bond pattern in a parallel p sheet, (b) Ball-and-stlck version of (a). The same color scheme is used as in Figure 2.5c. (c) Schematic diagram illustrating the pleat of a parallel p sheet.

The two peptides form a symmetrical dimer stabilized by four hydrogen bonds (red dashes) and hydrophobic contacts. The two monomers form a four-stranded, anti-parallel pleated sheet. 

Pleated p sheet (Section 27.19) Type of protein secondary structure characterized by hydrogen bonds between NH and C=0 groups of adjacent parallel peptide chains. The individual chains are in an extended zigzag conformation. 

FIGURE6.il The arrangement of hydrogen bonds in (a) parallel and (b) andparallel /3-pleated sheets. 

Figure 26.6 (a) The /3-pleated sheet secondary structure of proteins is stabilized by hydrogen bonds between parallel or antiparallel chains, (b) The structure of concanavalin A, a protein with extensive regions of antiparallel / sheets, shown as flat ribbons. 

Folding of a peptide probably occurs coincident with its biosynthesis (see Chapter 38). The physiologically active conformation reflects the amino acid sequence, steric hindrance, and noncovalent interactions (eg, hydrogen bonding, hydrophobic interactions) between residues. Common conformations include a-helices and P pleated sheets (see Chapter 5). 

The gene-encoded primary structure of a polypeptide is the sequence of its amino acids. Its secondary structure results from folding of polypeptides into hydrogen-bonded motifs such as the a helix, the P-pleated sheet, P bends, and loops. Combinations of these motifs can form supersecondary motifs. 

Two views of a pleated sheet, (a) The ball-and-stick view emphasizes the hydrogen bonding between the strands of the sheet, (b) The structural formula view emphasizes the folds of the sheet. 

The p-pleated sheet structure occurs in fibrous as well as globular proteins and is formed by intermolecular hydrogen bonds between a carboxyl group oxygen of one amino acid and an amine hydrogen of an adjacent polypeptide chain. Parallel p-pleated sheets form when the adjacent polypeptide chains are oriented in one direction (from N-terminal to C-terminal end or vice versa). Antiparallel p-pleated... 

The second structural element to be proposed by Pauling and Corey was the P-pleated sheet (Figure 4.7). These sheets are made up of P-strands, typically from 5 to 10 residues long, in an almost fully extended conformation, aligned alongside one another with hydrogen bonds formed between the C=0 bonds of one strand and the NH of the other, and vice versa. The P-sheets are pleated (i.e. they undulate) with the Ca atoms alternatively a little above, or a little below the plane of the P-sheet, which means that the side chains project alternatively above and below the plane. P-Strands can interact to form two types of pleated sheets. 

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.)... 

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