SYNOPSIS
A search procedure is described for making stereospecific assignments a t prochiral centers in proteins on the basis of nuclear Overhauser enhancement and coupling constant data derived from nmr experiments. A data b2,se comprising torsion angles, associated ' H-' H 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 +, 4 , and x, torsion angles. Both approaches are tested for P-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 P-methylene groups could he 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. ' 1!11)0 ,John Wiley & Sons, Inc. ( 'U' I )( )06-1525,'90/0408 1.3-10 $04 .OO