[The structure and function of the extracellular domain of human thyrotropin receptor]

Since the molecular cloning of human TSH receptor (TSHR), much efforts have been focused on determining the TSH or TSAb binding sites. Despite many conflicting data, there seems to be a consensus that TSH binds to the various parts of the extracellular domain of TSHR discontinuously. However, following questions are not yet answered 1) Is the binding to extracellular domain of TSHR sufficient to the signal transduction? 2) Is there any contribution of the extracellular loops to TSH binding? Using TSHR mutated at the first or the second extracellular loops, we propose that the extracellular loops are important for TSH binding and signal transduction.