COMPREHENSIVE NOE CHARACTERIZATION OF A PARTIALLY FOLDED LARGE FRAGMENT OF STAPHYLOCOCCAL NUCLEASE DELTA-131-DELTA, USING NMR METHODS WITH IMPROVED RESOLUTION

Comprehensive NOE results from detailed structural characterization of a 131 residue partially folded fragment of staphylococcal nuclease (D elta 131 Delta) made possible by NMR methods with improved resolution are presented. The resulting NOE patterns reflect sampling of both alp ha and beta regions of phi, phi conformational space, yet demonstrate significant preferences for both native-like and non-native-like turn and potentially helical conformations. Together with data from studies of the unfolded state of the drkN SH3 domain, NOE patterns observed f or partially folded or unfolded proteins are summarized. It is surpris ing that few long-range NOEs were observed in Delta 131 Delta. The two longest-range NOEs are both native-like; one of these, an (i,i + 5) N OE, provides evidence for a Schellman capping motif for helix terminat ion. Many aliphatic-aliphatic and aliphatic-amide NOEs, which are not normally observed in folded proteins, were detected. We have ruled out significant contributions from spin-diffusion for a number of these N OEs and suggest that one source may be sampling of non-prolyl cis pept ide bond configurations in the disordered state of Delta 131 Delta. (C ) 1997 Academic Press Limited.