PREDICTOR FOR SULFUR-AROMATIC INTERACTIONS IN GLOBULAR PROTEINS

The predictor, Y = 2.54 + (4 Met + 2 Arg ‐ Tyr) 83/N, where Y is the number of sulfur‐aromatic interactions in a globular protein and N is the total number of amino acids in the protein, accounts for 75% of the variation in this type of interaction that occurs in 22 globular proteins whose three‐dimensional structure has been determined. We find that S‐ interactions are not random events but rather are the outcome of a competition between the dipolar groups, amides and sulfur‐containing, for ring neighbors. This outcome is strongly weighted in favor of S‐ interactions by the presence in the protein of positively charged side‐chains; it is not affected by the number of strictly non‐polar side‐chains.