A SINGLE ARGININE RESIDUE DETERMINES SPECIES-SPECIFICITY OF THE HUMAN GROWTH-HORMONE RECEPTOR

Although growth hormone (GH) receptors (GHRs) in many species bind human (h) GH as well as their own GH, the hGHR only binds primate GH. Arg(43) in hGHR interacts with Asp(171) Of hGH. Nonprimates have a His in the position equivalent to residue 171 of primate GH and a Leu in position 43 of primate GHR. To determine whether Arg(43) accounts for the species specificity of the hGHR, point mutations that changed Leu(43) to Arg were introduced into the cDNAs encoding the bovine (b) GHR or the rat GK binding protein (GHBP) and these mutants or their wild-type (WT) counterparts were expressed in mouse L cells. Binding of hGH or bGH to transfected cells or to GHBP secreted into the incubation medium was assessed by displacement of I-125-labeled hGH, WT and mutant bGHR bound hGH with similar affinity, but the affinity of the mutant receptors for bGH was reduced 200-fold, Likewise, WT and mutant GHBP bound hGH with equal affinity, but only WT GHBP bound bGH, Cross-linking of I-125-labeled hGH to WT or mutant GHR produced a (141)-kDa labeled complex whose appearance was blocked by unlabeled hGH, but bGH blocked cross-linking only to WT receptors, Both hGH and bGH stimulated tyrosine phosphorylation of a 95-kDa protein in cells transfected with WT GHR, but bGH was less effective in cells expressing mutant GHR, We conclude that incompatibility of Arg(43) in the hGHR with His(171) in nonprimate GH is the major determinant of species specificity.