Expression of human endothelin receptor ETB by Escherichia coli transformants

Membrane fractions from Escherichia coli transformed with an expression vector for the human endothelin receptor ETB were found to exhibit specific and saturable binding sites for labeled ET-1. Binding properties were similar to those observed in eukaryotic cells: KD was 110 pM and the three endothelin isoforms were equipotent in competition experiments. The importance of the cysteines located in each of the three extracellular loops was assessed by replacing them individually with alanine residues. Impaired binding was observed in each case but the effect was far more pronounced for the cysteine mutants of the first and second loop pointing to their critical importance for active ETB expression.