Hydrogen Bond in P sheets

From these results, it can be said that the helix and (3-sheet forms of PLA, PG or PDA in the blend samples are incorporated into the PLIL or PLV in the (3-sheet form and then takes the (3-sheet form by forming hydrogen bonds with the (3-sheet form of PLIL or PLV. This means that polypeptide chains, by changing from the helix form to the (3-sheet form are hydrogen-bonded with p-sheet type polypeptide chains which are energetically more stable than the helix form of the polypeptide chains hydrogen-bonded by themselves. 

Figure 13.10 Rearrangements of the hydrogen bond network between strands 1, 2, and 3 in the p sheet of Go. as a consequence of the switch from the GDP (blue) to the GTP (green) conformation. Strand P3 pulls away from pi and disrupts two hydrogen bonds in order to bring Gly 199 into contact with the y-phosphate of GTP. As a consequence new hydrogen bonds are formed between P2 and P3. (Adapted from D. Lambright et al.. Nature 369 621-628,...

Whereas the 3-pleated sheet provides a particularly nice and easily appreciated example of regular hydrogen bonding in polypeptide chains, the most common arrangement found in proteins is actually the a-helix (Figure 13.2). Do not worry about the a or P used in the nomenclature this merely signifies that the helical structure (a) was deduced earlier than that of the pleated sheet (P). 

Two major elements of secondary structure are the a helix and the P strand. In the a helix, the polypeptide chain twists into a tightly packed rod. Within the helix, the CO group of each amino acid is hydrogen bonded to the NH group of the amino acid four residues farther along the polypeptide chain. In the (3 strand, the polypeptide chain is nearly lully extended. Two or more P strands connected by NH-to-CO hydrogen bonds come together to form (3 sheets. The strands in p sheets can be antiparallel, parallel, or mixed. 

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