Alpha helix
From Proteopedia
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A common fold found in transmembrane proteins are alpha-helical bundles running from one side to the other side of the membrane. An alpha helix of 19 amino acids (with a length of about 30 angstroms) has the right size to cross the double-layer of a typical membrane. If the helix runs at an angle instead of perfectly perpendicular to the membrane, it has to be a bit longer. There is a write-up on opioid receptiors in the Molecule of the Month series by David Goodsell (http://pdb101.rcsb.org/motm/217). | A common fold found in transmembrane proteins are alpha-helical bundles running from one side to the other side of the membrane. An alpha helix of 19 amino acids (with a length of about 30 angstroms) has the right size to cross the double-layer of a typical membrane. If the helix runs at an angle instead of perfectly perpendicular to the membrane, it has to be a bit longer. There is a write-up on opioid receptiors in the Molecule of the Month series by David Goodsell (http://pdb101.rcsb.org/motm/217). | ||
| - | ===Alpha helices in | + | ===Alpha helices in coiled coils=== |
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| + | [[Coiled coil]] | ||
Revision as of 18:39, 16 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.
