Use of 13C conformation-dependent chemical shifts to elucidate the local structure of a large protein with homologous domains in solution and solid state.

In order to clarify the difference between solution NMR and X-ray diffraction analyses concerning the presence of alpha-helical structure in protein A, the 13C conformation-dependent chemical shifts of the 13C-labeled carbonyl carbons for selectively labeled protein A were used. In the 13C CP/MAS NMR spectra, the higher-field shifts of the carbonyl carbons of 13C-labeled Thr and Val residues compared with the random coil chemical shifts both in solution and solid state imply the presence of the third helix in the polypeptide chain, in contrast to the crystal structure of Fc-bound B-domain. Thus, a combination of selective isotope labeling and conformation-dependent chemical shifts will be a good Indicator to monitor the local structure of homologous protein in solution and solid state.