Alpha helix
From Proteopedia
| Line 4: | Line 4: | ||
<jmol> | <jmol> | ||
<jmolButton> | <jmolButton> | ||
| - | <script> select visible; var a = [0. | + | <script> select visible; var a = [0.5, 0.7, 1.0, 1.5, 2.0]; for(var i IN a) {spacefill @i; delay 0.4;} |
</script> | </script> | ||
<text>increase sphere radii</text> | <text>increase sphere radii</text> | ||
Revision as of 19:31, 16 January 2018
Contents |
Structure and hydrogen bonding
| |||||||||||
Experimental evidence
a) CD spectroscopy http://www.cryst.bbk.ac.uk/PPS2/course/section8/ss-960531_21.html
b) NMR chemical shifts
Role of alpha helices in the history of structural biology
a) Pauling predicts it http://onlinelibrary.wiley.com/doi/10.1111/febs.12796/full
b) Determination of hand: There are several methods in X-ray crystallography where crystallographers obtain an electron density, but don't know whether it or its mirror image is correct. Historically, finding electron density that fits a helix was used to break this ambiguity. If the helix was right-handed, the electron density was used as is, but if the helix was left-handed, the mirror image was used.
c) Tracing the chain: When building a model into electron density, the first step was to place continguous C-alpha atoms into the density (with proper spacing). To see in which direction an alpha helix goes, you look at the side chain density. If it points up, the N-terminus is on top, otherwise on the bottom.
