The species specificity of growth hormone requires the cooperative interaction of two mofits

Primate growth hormones (GH) activate both primate and non-primate somatotr ophic receptors (GH receptors), but non-primate GHs do not activate primate CI-I receptors, Previous studies argued the interaction of Asp(171) of hum an GH and Arg(43) of the receptor produced an attractive ionic interaction. In non-primate GHs, His(170) replaces the homologous Asp(171), producing a repulsive interaction with Arg(43) of the primate receptor which was belie ved to reduce the attraction of non-primate GH for the human CH receptor, t hus providing species specificity. In this report, H170D bovine GH had acti vity and affinity for human GH receptors approaching those of human GH, In contrast, replacing Asp(171) of human GH with His did not significantly red uce somatotrophic activity, indicating that species specificity is not whol ly explained by this residue's interaction with Arg(43) of the receptor, De letion of either Phe(44) (a residue present only in primate GHs) or residue s 32-46 (20-kDa form of human GH) each only marginally reduced somatotrophi c activities, But the combination of the D171H mutation,vith either Delta P he(44) or Delta 32-46 in human GH reduced binding and activity in a greater than additive fashion, indicated a functional interaction between these di stant structural features, In bovine CII addition of phenylalanine at posit ion 44 increased the somatotrophic activity and receptor affinity in cells containing the human GH receptor. The combination of the H170D mutation and the addition of phenylalanine at position 44 created a bovine GH with acti vity indistinguishable from wild-type human GH. Based on evidence from both bovine and human GHs, the cooperative interaction of these two distant mot ifs determined the species specificity and indicated that structural plasti city was a critical feature necessary for the species specificity of somato trophic activity. (C) 2000 Federation of European Biochemical Societies.