Alpha helix
From Proteopedia
Karsten Theis (Talk | contribs)
(New page: ==Structure and hydrogen bonding== <StructureSection load='1stp' size='340' side='right' caption='Caption for this structure' scene=''> Secondary structure, right-handed helix, 3.6 resid...)
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Revision as of 22:13, 12 January 2018
Contents |
Structure and hydrogen bonding
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Experimental evidence
a) CD spectroscopy b) NMR chemical shifts c) Fiber diffraction
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.
