Turns in Proteins: Difference between revisions

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 Turn 2mhr 5-8, classIVB, is shown in the applet on the right. Notice that it does not have a hydrogen bond and that the backbone atoms of the first and fourth residues are not in position to form a hydrogen bond because the presence of a cis peptide bond. (<scene name='Turns_in_Proteins/2mhr_5-8c/2'>Initial scene</scene>) <scene name='Turns_in_Proteins/2mhr_114-117b/2'>Compare</scene> with a turn which has a hbond.  The oxygen and nitrogen of the <scene name='Turns_in_Proteins/2mhr_88-91b/2' >cis peptide bond</scene> project from the same edge of the plane, whereas with the trans peptide bonds they project from opposite edges of the plane. The <scene name='Turns_in_Proteins/Rama_8_turns/6'>Ramachandran plot</scene> of the eight turns shown above.  Two residues of each turn are plotted giving a total of 16 points.  Hover the cursor over a sphere to identify the residue name and number.  Realize that, in most cases, the spheres that are of the same class and are close to each other are not part of the same turn.  Notice that Gly is the only residue in a [[Ramachandran Plot|disallowed region]] since other residues at those positions could not generate the angles necessary to form the turn and that Pro is the third residue in both class IVB turns.
 == Gamma Turns ==
-γ-turns consist of three residues and contain a hydrogen bond between residues one and three.  In a search of 54 proteins nine proteins  were found to have eleven  classic γ-turns, and these eleven turns had mean phi and psi values at residue ''i'' + 1 of +75.0 and -64, respectively.<ref name="Miner">Miner-White, EJ, et. al. ''One type of gamma turn, rather than the other, gives rise to chain reversal in proteins''. J. Mol. Bio. '''204''', 1983, pp. 777-782.</ref> Seven of these eleven turns are involved in the formation of β-hairpins which produce a reversal in the peptide chain. An example of a classic γ-turn producing this effect is in <scene name='Turns_in_Proteins/2alp_classic/1'>α-lytic protease</scene> (2alp). The inverse γ-turns have mean phi and psi values at residue ''i'' + 1 of -79 and +69, respectively. In their search of proteins Miner-White, et. al. revealed that inverse γ-turns are more common than the classic because in the 54 proteins searched they found 61 inverse γ-turns, but only one formed a β-hairpins producing a reversal in the peptide chain.<ref name="Miner" />  The γ-turns are not as common as the β-turns.
+Gamma turns consist of three residues and contain a hydrogen bond between residues one and three.  In a search of 54 proteins nine proteins  were found to have eleven  classic γ-turns, and these eleven turns had mean phi and psi values at residue ''i'' + 1 of +75.0 and -64, respectively.<ref name="Miner">Miner-White, EJ, et. al. ''One type of gamma turn, rather than the other, gives rise to chain reversal in proteins''. J. Mol. Bio. '''204''', 1983, pp. 777-782.</ref> Seven of these eleven turns are involved in the formation of β-hairpins which produce a reversal in the peptide chain. An example of a classic γ-turn producing this effect is in <scene name='Turns_in_Proteins/2alp_classic/1'>α-lytic protease</scene> (2alp). The inverse γ-turns have mean phi and psi values at residue ''i'' + 1 of -79 and +69, respectively. In their search of proteins Miner-White, et. al. revealed that inverse γ-turns are more common than the classic because in the 54 proteins searched they found 61 inverse γ-turns, but only one formed a β-hairpins producing a reversal in the peptide chain.<ref name="Miner" />  The γ-turns are not as common as the β-turns.
 === Examples ===
 <scene name='Turns_in_Proteins/Domain2/3'>Gamma turns</scene> in domain 2 of chain A of glycogen phosphorylase.
 ==Notes and References==