Secondary structure and hydrogen bonding of crambin in solution A two‐dimensional NMR study

Abstract
The secondary structure of crambin in solution has been determined using two‐dimensional NMR and is found to be essentially identical to that of the crystal structure. The H–D exchange of most amide protons can be accounted for in terms of the hydrogen bonds found in the X‐ray structure. Exceptions are the amide protons of Cys‐4 and Ser‐6, which exchange more slowly than expected, and of Asn‐46 for which the exchange is faster. These results might be explained by a slightly different conformation of the C‐terminal region of the protein in solution. The slow exchange of the amides of Cys‐32 and Glu‐23 might be due to aggregation involving an extremely hydrophobic part of the protein in solution.