Table 1.

Effect of mutation of aspartic acid residue 2.50 in the second transmembrane-spanning region of GPCRs

Receptor	G protein coupling	Agonist signalling	Agonist affinity	Na+ sensitivity of agonist binding	Comments	Reference
α2-adrenergic	↓	↓	⇔ Some increase	Lost		Horstman et al. (1990); Wang et al. (1991); Ceresa and Limbird (1994)
β2-adrenergic	↓	↓	↓↓	—	Agonist affinity reduced (10-fold (isoprenaline), 70-fold (noradrenaline)	Strader et al. (1987, 1988); Chung et al. (1988); Liapakis et al. (2004)
D2 dopamine	↓	↓	↓	Lost	Agonist affinity reduced ∼3-fold	Neve et al. (1991)
5-HT1A	↓	↓	⇔	—		JT Alder and PG Strange, unpublished data
5-HT2A	↓	↓	⇔	—		Wang et al. (1993)
m1 muscarinic	—	↓	⇔ Some increased	—		Fraser et al. (1989)
TRH	—	↓	↓	—		Perlman et al. (1992)
Tachykinin NK2	—	↓	⇔	—	D79N mutant shows unchanged agonist affinity, whereas D79A mutant shows reduced affinity	Donnelly et al. (1999)
Neurotensin NTR1	⇔	↓	⇔	↓		Martin et al. (1999)
δ-opioid	⇔	⇔	↓	Lost		Kong et al. (1993b)
Somatostatin (SSTR2)	⇔	⇔	⇔	Lost		Kong et al. (1993a)

Abbreviation: GPCR, G protein-coupled receptor.