| The gonadotropins are alpha/beta heterodimer hormones of the anterior pituitary that control reproduction. Little is known about the interaction of these hormones with their receptors or how this interaction leads to signal transduction. The studies described were designed to identify domains of the lutropin receptor involved in hormone contact. To that end, a homolog scanning approach was utilized in order to optimize the expression of properly folded analogs on the cell surface. Chimaeras were constructed to provide ligand binding, as negative results were expected to be largely uninterpretable. A lack of hormone binding could indicate the loss of critical residues resulting in a disruption of folding, processing, or transportation. Chimaeras prepared by combining portions of the LH and b 2-adrenergic receptors determined that the extracellular domain of the full length LH receptor was primarily responsible for high affinity ligand binding, and that the interaction between the extracellular and transmembrane domains were required for receptor cell surface expression. Using chimaeras of LH and FSH receptors, hCG specificity determinants were identified between residues 93 and 170. Those residues responsible for FSH specificity were found both N- and C-terminal to the domain defined for hCG specificity. Using chimaeras of rat and human LH receptors, amino acid residues were identified within the carboxy terminal region of the human LH receptor extracellular domain which prevented bovine LH binding. Unlike the rat LH receptor, the human LH receptor is unable to recognize bovine LH, a lutropin similar to hCG. Collectively, these observations support a model of glycoprotein hormone interaction where specificity of interaction is determined both through domains of high affinity within the receptor amino terminal 200 residues and negative determinants within the carboxy terminal end of the receptor extracellular domain. |
