Organization of regions with amphiphilic alpha-helical potential within the three-dimensional structure of beta-sheet proteins.

The observation that strong amphiphilic alpha-helical potential exists in all proteins, including beta-sheet proteins, has given rise to the idea that alpha-helical intermediates may be critical to the folding paths of all proteins. Here we report that regions with amphiphilic alpha-helical potential in beta-sheet proteins are regularly spaced within the native structure of the proteins at an average interval of about 13 A. This regular spacing did not occur when the location of amphiphilic regions was randomly assigned (p = 0.0056), suggesting some degree of organization with respect to the native fold. However, in the native structure of various non-homologous proteins that contain the same fold, the location of the regions with amphiphilic alpha-helical potential was not conserved. Further, there was no apparent association of amphiphilic alpha-helical potential with any particular type of secondary structure, confirming that this potential is not involved in maintenance of native structure and suggesting that it may be associated with a highly adaptable process.