Abstract: It is shown
that the averaged chemical shift (ACS) of a particular nucleus in the protein
backbone empirically correlates well to its secondary structure content (SSC).
Chemical shift values of more than 200 proteins obtained from the Biological
Magnetic Resonance Bank are used to calculate ACS values, and the SSC is
estimated from the corresponding three-dimensional coordinates obtained from
the Protein Data Bank. ACS values of (1)H(alpha) show the highest correlation
to helical and sheet structure content (correlation coefficient of 0.80 and
0.75, respectively); (1)H(N) exhibits less reliability (0.65 for both sheet
and helix), whereas such correlations are poor for the heteronuclei. SSC
estimated using this correlation shows a good agreement with the conventional
chemical shift index-based approach for a set of proteins that only have
chemical shift information but no NMR or x-ray determined three-dimensional
structure. These results suggest that even chemical shifts averaged over
the entire protein retain significant information about the secondary structure.
Thus, the correlation between ACS and SSC can be used to estimate secondary
structure content and to monitor large-scale secondary structural changes
in protein, as in folding studies.