1H‐Nmr stereospecific assignments by conformational data‐base searches

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Abstract
A search procedure is described for making stereospecific assignments at prochiral centers in proteins on the basis of nuclear Overhauser enhancement and coupling constant data derived from nmr experiments. A data base comprising torsion angles, associated 1H‐1H coupling constants and interproton distances is searched by a computer algorithm for sets of values that match the experimental data within specified error limits. Two different data bases are used. The first is a crystallographic data base derived from 34 well‐refined crystal structures; the second is a systematic data base derived from conformations of a short peptide fragment with idealized geometry by systematically varying the ϕ,ψ, and χ1 torsion angles. Both approaches are tested for β‐methylene groups with model data obtained from 20 crystal structures. The results for the two methods are similar though not identical, so that a combination of the two methods appears to be useful. With an appropriate choice of error estimates, around 80% of the β‐methylene groups could be assigned in the test calculations. In addition, results with experimental nmr data indicate that a similar percentage of stereospecific assignments can be made in practical situations.