A GROWTH-HORMONE AGONIST PRODUCED BY TARGETED MUTAGENESIS AT BINDING-SITE-1 - EVIDENCE THAT SITE-1 REGULATES BIOACTIVITY

Growth hormone (GH) is believed to signal by dimerizing its receptor t hrough two binding sites on the hormone, Previous attempts to increase the biopotency of GH by increasing its site 1 affinity have been unsu ccessful, which has led to a bias toward engineering site 2 interactio ns in the quest for creation of super agonists, Here we report that in creasing site 1 affinity can markedly increase proliferative bioactivi ty in FDC-P1 cells expressing full-length GHR, In contrast, we find th ree site 1 mutants with affinities for site one similar to or greater than wild type GH, which have markedly decreased bioactivity. Through crystal structure analysis of the receptor interactive regions of thes e GH analogues, we are able to suggest why previous mutagenesis on hum an GH failed to improve biopotency, and thus provide a new avenue for GH and cytokine agonist design.