An NMR study on the beta-hairpin region of barnase.
BACKGROUND
The beta-hairpin of barnase (residues Ser92-Leu95) has been proposed in theoretical and protein engineering studies to be an initiation site for folding [1]. There is evidence for residual structure in this region from NMR studies of the denatured protein under different denaturing conditions [2,3]. A more detailed analysis is possible by NMR studies of isolated fragments.


RESULTS
Protons of fragments B(80-110) and B(69-110) in 6 M urea have non-random chemical shifts. Non-native long-range and medium-range NOE contacts with the aromatic moiety of Trp94 indicate that it is involved in a beta-turn-like or alpha-helix-like conformation. Also, the sidechains of Trp71, Tyr79, Phe82, Tyr90, Tyr97, His102, Tyr103 and Phe106 show non-native hydrophobic contacts. Non-random conformational shifts and sequential NN(i,i+1) NOE contacts are clustered to one of the beta-strands and one of the loop regions.


CONCLUSIONS
The hairpin region of barnase adopts beta-turn-like or alpha-helix-like conformations, which are weakly populated even in 6 M urea. The hairpin region is a potential nucleation site in folding that may consolidate on docking with the first alpha-helix. The other residues that have conformational preferences from a beta-strand and one of the loop regions in the native intact protein, but they do not constitute a nucleation site.
Neira
J L
JL
MRC Unit for Protein Function and Design, Cambridge Centre for Protein Engineering, UK.
Fersht
A R
AR
D000595:Amino Acid Sequence; D001426:Bacterial Proteins; D009682:Magnetic Resonance Spectroscopy; D008958:Models, Molecular; D008969:Molecular Sequence Data; D010446:Peptide Fragments / Q000737:chemistry / Q000235:genetics; D011487:Protein Conformation; D011489:Protein Denaturation; D017510:Protein Folding; D017433:Protein Structure, Secondary; D012260:Ribonucleases / Q000737:chemistry* / Q000235:genetics; D013816:Thermodynamics; D014508:Urea
D001426:Bacterial Proteins; D010446:Peptide Fragments; D014508:Urea; D012260:Ribonucleases; C019760:Bacillus amyloliquefaciens ribonuclease