Lys 199 mutation of the human angiotensin type 1 receptor differentially affects the binding of surmountable and insurmountable non-peptide antagonists

Many slow dissociating (insurmountable) non-peptide angiotensin type 1 receptor (AT 1 ) antagonists contain, besides the acidic biphenyltetrazole substructure of losartan, a second acidic group to stabilise antagonist-receptor complexes. To investigate the involved basic amino-acids of the human AT 1 -receptor, wild-type and mutant receptors were transiently transfected in CHO-K1 cells and characterised by 3 Hcandesartan binding. Lys 199 → Gln substitution decreased the affinity 45-fold for candesartan (95% insurmountable), 18-fold for EXP3174 (70% insurmountable), 10-fold for irbesartan (40% insurmountable) and 5-fold for losartan (surmountable). His 256 → Ala substitution had only minor effects. This suggests that Lys 199 is important for the tight binding of non-peptide antagonists.