STRUCTURE AND DYNAMICS OF A DENATURED 131-RESIDUE FRAGMENT OF STAPHYLOCOCCAL NUCLEASE - A HETERONUCLEAR NMR-STUDY

Citation
At. Alexandrescu et al., STRUCTURE AND DYNAMICS OF A DENATURED 131-RESIDUE FRAGMENT OF STAPHYLOCOCCAL NUCLEASE - A HETERONUCLEAR NMR-STUDY, Biochemistry, 33(5), 1994, pp. 1063-1072
Citations number
45
Categorie Soggetti
Biology
Journal title
ISSN journal
00062960
Volume
33
Issue
5
Year of publication
1994
Pages
1063 - 1072
Database
ISI
SICI code
0006-2960(1994)33:5<1063:SADOAD>2.0.ZU;2-W
Abstract
A partially folded form of staphylococcal nuclease has been obtained b y deleting residues 4-12 and 141-149 of the 149-residue wild-type prot ein. Sequence-specific NMR resonance assignments have been obtained fo r 106 of the 131 residues in this protein fragment by using multi-dime nsional triple resonance NMR of samples enriched with C-13 and N-15. R esidues corresponding to helix 2 (residues 98-106) and helix 1 (residu es 54-68) of the native state give chemical shifts and NOE effects cha racteristic of helical structure. These same residues, however, give c oupling constants and NOE effects indicative of fast conformational av eraging between helical and extended conformations. The residual helix structure observed in the nuclease fragment is thus considerably less persistent than the corresponding structure in the native state. Base d on H alpha chemical shifts, we estimate the fractional population of helical conformers to be 30% for helix 2 and 10% for helix 1. Two seg ments, 83-86 and 94-97, show NOE effects, coupling constants, and lowe red amide temperature coefficients consistent with a native-like rever se-turn structure. The C-terminal alpha-helix as well as the fourth an d fifth strands of the 5-strand beta-barrel show little evidence for o rdered structure. The first three strands of the beta-sheet, part of t he catalytic loop, and the first turn of helix 3 give significantly po orer NMR data than the rest of the protein, possibly as a result of ex change broadening, and could not be characterized in detail. That the most persistent elements of structure in the fragment are native-like suggests that nuclease may fold by a hierarchical mechanism.