NMR study of the differential contributions of residues of transforming growth factor alpha to association with its receptor

A heteronuclear NMR study of human transforming growth factor alpha (TGF al pha) in complex with the epidermal growth factor receptor extracellular dom ain (EGFR-ED) provided an effective method for delineating the relative con tributions of the residues of the ligand to its affinity for the receptor. In conjunction with previously obtained mutagenesis data, these results ind icate that while a large number of residues are involved in complex formati on and make up the binding interface, a small subset contribute most of the binding energy. They also show that while the residues which contribute to receptor binding are localized on one face of the molecule, the specific r esidues that play the major role in the affinity of TGF alpha in the comple x are in two distinct regions of TGF alpha, This suggests that two small fu nctional epitopes each composed of two residues exist within a larger struc tural epitope presented on the binding face, These results give the most de tailed picture to date of the receptor binding determinants and yield furth er insight into the formation of the ligand-receptor complex.