Alpha helix: Difference between revisions
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Proline is considered a helix breaker because its main chain nitrogen is not available for hydrogen bonding. Here is an example of a <scene name='77/778341/Proline/1'>kink in a helix</scene> (<jmol> | Proline is considered a helix breaker because its main chain nitrogen is not available for hydrogen bonding. Here is an example of a <scene name='77/778341/Proline/1'>kink in a helix</scene> (<jmol> | ||
<jmolLink> | <jmolLink> | ||
<script> select 58-61:A; structure turn; select 50-58:A; rockets on; select 60-68; rockets on; | <script> select 58-61:A; structure turn; select 50-58:A; rockets on; select 60-68:A; rockets on; | ||
</script> | </script> | ||
<text>show helical axes with rockets</text> | <text>show helical axes with rockets</text> | ||
</jmolLink> | </jmolLink> | ||
</jmol> ) at the position of a <scene name='77/778341/Proline/2'>proline</scene>. | </jmol>) at the position of a <scene name='77/778341/Proline/2'>proline</scene>. | ||
Prolines are often found near the beginning or end of an alpha helix, as in this example of <scene name='77/778341/Proline_cap/1'>the helix in crambin</scene> (this is an ultra high resolution structure where hydrogen atoms - white - are resolved and some atoms are shown in multiple positions). At the <scene name='77/778341/Proline_cap_detail/2'>C-terminal end</scene> of the helix, there is a proline that interrupts the regular pattern of n to n+4 hydrogen bonds. Instead, the helix ends with an n to n+3 hydrogen bond (one turn of a so-called 3-10 helix, see [[Helices in Proteins]]). The subsequent proline is in the center of a turn, followed by a glycine (which is part of an n to n+3 hydrogen bond also typical for turns). | Prolines are often found near the beginning or end of an alpha helix, as in this example of <scene name='77/778341/Proline_cap/1'>the helix in crambin</scene> (this is an ultra high resolution structure where hydrogen atoms - white - are resolved and some atoms are shown in multiple positions). At the <scene name='77/778341/Proline_cap_detail/2'>C-terminal end</scene> of the helix, there is a proline that interrupts the regular pattern of n to n+4 hydrogen bonds. Instead, the helix ends with an n to n+3 hydrogen bond (one turn of a so-called 3-10 helix, see [[Helices in Proteins]]). The subsequent proline is in the center of a turn, followed by a glycine (which is part of an n to n+3 hydrogen bond also typical for turns). | ||
