Amino acid residues in the transmembrane domain of the type 1 sigma receptor critical for ligand binding

The type 1 sigma receptor expressed in Xenopus oocytes showed binding abili ties for the sigma-1 ligands, [H-3](+)pentazocine and [H-3]NE-100, with sim ilar kinetic properties as observed in native tissue membranes. Amino acid substitutions (Ser99Ala, Tyr103Phe and di-Leu105,106di-Ala) in the transmem brane domain did not alter the expression levels of the type 1 sigma recept or as determined by immunoblot analysis using an anti-type 1 sigma receptor antiserum. fly contrast, ligand binding was significantly suppressed by th e substitutions. These findings provide evidence that the transmembrane dom ain of the type 1 sigma receptor plays a critical role in ligand binding of this receptor. (C) 1999 Federation of European Biochemical Societies.