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Chemical Shift Index (Secondary structure of Amino Acids)

The formation of the chemical shift index is a method to determine the secondary structure of proteins from the chemical shifts of backbone atoms. It is based on the chemical shifts listed in the following table (+- 0.7ppm).

The following simple rules are applied:

1 is assigned if the measured chemical shift is greater than the CSI value range.
-1 is assigned, if the measured chemical shift is smaller than the CSI value range.
0 is assigned if the measured chemical shift lies within the value range.
To determine the secondary structure, proceed as follows:

The alpha helix is defined if four or more “-1” HA and/or “1” CA/CO are found one after the other.
A beta strand is defined when three or more “1” HA and/or “-1” CA/CO are found one after the other.
All other ranges are called coils.

HACACBCO
Ala            4.35   52.5   19.0   177.1    
Cys            4.65   58.8   28.6   174.8
Asp            4.76   54.1   40.8   177.2
Glu            4.29   56.7   29.7   176.1
Phe            4.66   57.9   39.3   175.8
Gly            3.97   45.0   -      173.6
His            4.63   55.8   32.0   175.1
Ile            3.95   62.6   37.5   176.8
Lys            4.36   56.7   32.3   176.5
Leu            4.17   55.7   41.9   177.1
Met            4.52   56.6   32.8   175.5
Asn            4.75   53.6   39.0   175.5
Pro            4.44   62.9   31.7   176.0
Gln            4.37   56.2   30.1   176.3
Arg            4.38   56.3   30.3   176.5
Ser            4.50   58.3   62.7   173.7
Thr            4.35   63.1   68.1   175.2
Val            3.95   63.0   31.7   177.1
Trp            4.70   57.8   28.3   175.8
Tyr            4.60   58.6   38.7   175.7
Source: http://triton.iqfr.csic.es/guide/eNMR/proteins/chemshift.html

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