Stereochemistry of the interaction between methionine sulfur and the protein core

The stereochemical features of the interaction between the sulfur atom of methionine residues and surrounding atoms are examined on a large set of known protein crystal structures. It appears that the minimum energy conformations observed in small molecule crystals are not observed within the protein core. This suggests that these interactions are either of little intensity, though they might contribute to regulate the protein physiological behavior, or physicochemically different from their counterpart in small molecule crystals.