J. Balbach et al., DETECTION OF RESIDUE CONTACTS IN A PROTEIN-FOLDING INTERMEDIATE, Proceedings of the National Academy of Sciences of the United Statesof America, 94(14), 1997, pp. 7182-7185
Protein folding can be described in terms of the development of specif
ic contacts between residues as a highly disordered polypeptide chain
converts into the native state. Here we describe an NMR based strategy
designed to detect such contacts by observation of nuclear Overhauser
effects (NOEs). Experiments with alpha-lactalbumin reveal the existen
ce of extensive NOEs between aromatic and aliphatic protons in the arc
hetypal molten globule formed by this protein at low pH. Analysis of t
heir time development provides direct evidence for near-native compact
ness of this state. Through a rapid refolding procedure the NOE intens
ity can be transferred efficiently into the resolved and assigned spec
trum of the native state. This demonstrates the viability of using thi
s approach to map out time-averaged interactions between residues in a
partially folded protein.