| Popis: |
Heterologous expression of the human neurotensin receptor type I (hNT1-R) has been achieved in the yeast Saccharomyces cerevisiae. Immunoanalysis of membranes prepared from cells expressing a c-myc-tagged version of hNT1-R revealed multiple c-myc cross-reacting polypeptides of high molecular mass, suggesting that hNT1-R was glycosylated in yeast. High-affinity binding sites for 125I-labeled-[monoiodo-Tyr3]neurotensin ([125I-Tyr3]NT) were detected on hNT1-R-expressing cells with Kd and Bmax values of 3.2 nM and of 500 receptors per cell, respectively. Competition binding studies of neurotensin with SR142948 and SR48692, two nonpeptidic antagonists of hNT1-R, indicated that the yeast-produced recombinant receptor displayed the same pharmacological properties as hNT1-R expressed in mammalian cells. Interestingly, neurotensin activated the pheromone pathway in hNT1-R-expressing cells in a dose-dependent fashion, as revealed by a beta-galactosidase activity assay with a pheromone-responsive Fus1:lacZ construct. Mutational inactivation of the SST2 and STE2 genes increased the level of beta-galactosidase activity in response to neurotensin by twofold. Recombinant hNT1-R-producing cells, which lacked the endogenous G-protein-coupled receptor for the alpha pheromone, mated with wild-type MATalpha haploid cells in response to neurotensin, leading to bona fide diploid zygote formation. This is the first report of a mammalian receptor that can replace the endogenous pheromone receptor when produced in yeast, by signaling a fully effective, agonist-induced, mating process. |
