User:Karsten Theis/turns

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===Role in protein folds===
===Role in protein folds===
The repetitive secondary structure elements (alpha helices and beta strands) go in a single direction. Turns change the direction of the main chain, allowing them to connect alpha helices and beta strands at the surface of a globular protein. Of the six main chain hydrogen bonding partners of a turn, a maximum of two are engaged in hydrogen bonding, and turns are rarely found in the hydrophobic core. Below are three different protein folds highlighting the role of turns and their positions within a fold.
The repetitive secondary structure elements (alpha helices and beta strands) go in a single direction. Turns change the direction of the main chain, allowing them to connect alpha helices and beta strands at the surface of a globular protein. Of the six main chain hydrogen bonding partners of a turn, a maximum of two are engaged in hydrogen bonding, and turns are rarely found in the hydrophobic core. Below are three different protein folds highlighting the role of turns and their positions within a fold.
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====Turns in an all-alpha protein====
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In this <scene name='10/1072233/Alpha_2hmr/1'>myohemerythrin</scene> protein, you can see beta turns connecting the anti-parallel alpha helices. You can <jmol><jmolLink>
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<script>
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view1 = script("show moveto")[11][0];
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select (67-70 and mainchain) or (68-69 and *.CB);
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wireframe 0.3;
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color cpk;
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select 67-70;
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backbone off;
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delay 0.5;
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moveto 1.0 { 455 178 -872 110.43} 935.76 0.0 0.0 {26.793 33.036 8.6745} 44.96343106192573 {0 0 0} 0 0 0 3.0 0.0 0.0;
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slab on
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slab 60
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delay 6;
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select 67-70; backbone 0.4; wireframe off;
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slab off;
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script inline @{"moveto 1.0" + view1};
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</script>
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<text>zoom in</text>
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</jmolLink>
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</jmol> on the turn shown in the initial scene (and used below to explore conformations).
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====Turns in an all-beta protein====
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In this <scene name='10/1072233/Agglutinin/1'>agglutinin protein</scene>, you can see beta turns connecting the strands of anti-parallel beta sheets. Here is an alternate representation using <scene name='10/1072233/Agglutinin/2'>secondary structure cartoons</scene>.
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====Turns in an alpha/beta protein====
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In this <scene name='10/1072233/Tim/1'>TIM barrel protein</scene>, you can see beta turns connecting helices and strands. Here is an alternate representation using <scene name='10/1072233/Tim/2'>secondary structure cartoons</scene>.
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<jmol>
<jmol>
Line 115: Line 146:
</jmol>
</jmol>
-
====Turns in an all-alpha protein====
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===Exploring torsion angles of turns===
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In this <scene name='10/1072233/Alpha_2hmr/1'>myohemerythrin</scene> protein, you can see beta turns connecting the anti-parallel alpha helices. You can <jmol><jmolLink>
+
-
<script>
+
-
view1 = script("show moveto")[11][0];
+
-
select (67-70 and mainchain) or (68-69 and *.CB);
+
-
wireframe 0.3;
+
-
color cpk;
+
-
select 67-70;
+
-
backbone off;
+
-
delay 0.5;
+
-
moveto 1.0 { 455 178 -872 110.43} 935.76 0.0 0.0 {26.793 33.036 8.6745} 44.96343106192573 {0 0 0} 0 0 0 3.0 0.0 0.0;
+
-
slab on
+
-
slab 60
+
-
delay 6;
+
-
select 67-70; backbone 0.4; wireframe off;
+
-
slab off;
+
-
script inline @{"moveto 1.0" + view1};
+
-
</script>
+
-
<text>zoom in</text>
+
-
</jmolLink>
+
-
</jmol> on the turn shown in the initial scene (and used below to explore conformations).
+
-
 
+
-
====Turns in an all-beta protein====
+
-
In this <scene name='10/1072233/Agglutinin/1'>agglutinin protein</scene>, you can see beta turns connecting the strands of anti-parallel beta sheets. Here is an alternate representation using <scene name='10/1072233/Agglutinin/2'>secondary structure cartoons</scene>.
+
-
 
+
-
 
+
-
====Turns in an alpha/beta protein====
+
-
 
+
-
In this <scene name='10/1072233/Tim/1'>TIM barrel protein</scene>, you can see beta turns connecting helices and strands. Here is an alternate representation using <scene name='10/1072233/Tim/2'>secondary structure cartoons</scene>.
+
-
 
+
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===Exploring turns===
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The interactive Jmol window shows a <scene name='10/1072233/Turn_2mhr/1'>turn</scene> (residues 67-70 of the [[2hmr]] structure shown previously) that you can explore. Four consecutive amino acids are said to form a beta turn if the alpha carbon atoms of the first and the fourth residue are in close proximity (less than 7.0 or 7.5 Angstrom<ref>PMID:36293166</ref>). However, this also happens in alpha helices and 3(10) helices, and these are not classified as beta turn.
The interactive Jmol window shows a <scene name='10/1072233/Turn_2mhr/1'>turn</scene> (residues 67-70 of the [[2hmr]] structure shown previously) that you can explore. Four consecutive amino acids are said to form a beta turn if the alpha carbon atoms of the first and the fourth residue are in close proximity (less than 7.0 or 7.5 Angstrom<ref>PMID:36293166</ref>). However, this also happens in alpha helices and 3(10) helices, and these are not classified as beta turn.

Revision as of 15:23, 13 February 2025

A beta turn is a secondary structure element consisting of four consecutive amino acids (or three consecutive peptide planes). The geometry of turns correspond to a change in the direction of the polypeptide backbone, with a short distance between the first and fourth alpha carbon.

Facts you can learn and explore here

  1. A beta turn is a secondary structure element distinct from (but sometimes overlapping with) alpha helices and beta strands
  2. Beta turns consist of stretches of four amino acids making a sharp turn, with a short distance between the first and last alpha carbon
  3. Beta turns typically occur near the surface of globular proteins, often connecting helices and strands
  4. There are multiple types of beta turns, distinguished by the torsion angles of the second and third residue
  5. Glycine and proline occur relatively often in beta turns and play distinct special roles

See the discussion tab for learning and teaching notes.

Turns in 3D

                                                             Phi  2    3

                                                             Psi  2    3    

Drag the structure with the mouse to rotate

Further reading

  • Turns in Proteins
  • [betaturn.com] allows you to brows a protein database for turns of different types

References

  1. ↑ de Brevern AG. A Perspective on the (Rise and Fall of) Protein β-Turns. Int J Mol Sci. 2022 Oct 14;23(20):12314. PMID:36293166 doi:10.3390/ijms232012314
  2. ↑ Wilmot CM, Thornton JM. Analysis and prediction of the different types of beta-turn in proteins. J Mol Biol. 1988 Sep 5;203(1):221-32. PMID:3184187 doi:10.1016/0022-2836(88)90103-9

Proteopedia Page Contributors and Editors (what is this?)

Karsten Theis

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