Table 2

Mutational analysis of the adenosine A₁ with respect to ligand binding

Mutation^2-a	Species	Helix/position^2-b	Effect on Ligand Binding and Signal Transduction	Reference
G14T	H	1.37	Increased agonist affinity	Rivkees et al., 1999a
E16A/Q	H	1.39	Agonist affinity reduced 4- to 40-fold; little change in antagonist affinity	Barbhaiya et al., 1996
P25L	H	1.48	Modest reduction of agonist affinity	Rivkees et al., 1999a
I31C	H	1.54	No changes in radioligand binding	Rivkees et al., 1999a
C46A/S	H	2.41	No changes in radioligand binding	Scholl and Wells, 2000
S50A	H	2.45	No changes in radioligand binding	Barbhaiya et al., 1996
D55A	H	2.50	Increase in agonist affinity with no change in antagonist affinity; disrupted regulation of agonist binding by sodium ions	Barbhaiya et al., 1996
L65F	H	2.60	No changes in radioligand binding	Rivkees et al., 1999a
C80A/S	H	3.25	No detectable radioligand binding	Scholl and Wells, 2000
M82F	H	3.27	No changes in radioligand binding	Rivkees et al., 1999a
C85A	H	3.30	No changes in radioligand binding	Scholl and Wells, 2000
C85S			Agonist affinity reduced 4- to 13-fold; no change in antagonist affinity	Scholl and Wells, 2000
P86F	H	3.31	Substantial reduction of agonist binding	Rivkees et al., 1999a
V87A	H	3.32	No change in ligand affinity	Rivkees et al., 1999a
L88A	H	3.33	Substantial reduction of agonist binding, but also of N-0840 antagonist binding	Rivkees et al., 1999a
T91A	H	3.36	Substantial reduction of agonist binding, but also of N-0840 antagonist binding	Rivkees et al., 1999a
Q92A	H	3.37	Substantial reduction of agonist binding, but also of N-0840 antagonist binding	Rivkees et al., 1999a
S93A	H	3.38	No changes in radioligand binding	Barbhaiya et al., 1996
S94A	H	3.39	No detectable agonist or antagonist binding	Barbhaiya et al., 1996
S94T			Minor changes in ligand binding	Barbhaiya et al., 1996
A125K	H	4.43	No changes in radioligand binding	Rivkees et al., 1999a
C131A/S	H	4.49	No changes in radioligand binding	Scholl and Wells, 2000
S135A	H	4.53	No changes in radioligand binding	Barbhaiya et al., 1996
T141A	H	4.59	No changes in radioligand binding	Barbhaiya et al., 1996
F144L	H	4.62	No changes in radioligand binding	Rivkees et al., 1999a
C169A/S	H		No detectable radioligand binding	Scholl and Wells, 2000
H251L	B	6.52	Antagonist affinity reduced 4-fold; no change in agonist affinity	Olah et al., 1992
C255A/S	H	6.56	No changes in radioligand binding	Scholl and Wells, 2000
C260A/S	H		No changes in radioligand binding	Scholl and Wells, 2000
C263A/S	H		No changes in radioligand binding	Scholl and Wells, 2000
I270M M270I	B, C	7.35	Amino acid in position 270 contributes to canine/bovine A₁ AR binding selectivity	Tucker et al., 1994
T277A	H	7.42	400-fold decrease in affinity of NECA with modest changes in affinity for R-PIA andS-PIA (intact cells); substantial decrease in affinity of all agonists (membranes); no change in antagonist affinity	Townsend-Nicholson and Schofield, 1994;Dalpiaz et al., 1998
T277S			Modest decrease in agonist affinity; no change in antagonist affinity; nature of residue in position 277 also involved in canine/bovine A₁ AR binding specificity	Tucker et al., 1994; Townsend-Nicholson and Schofield, 1994
H278L	B	7.43	Negligible agonist and antagonist binding	Olah et al., 1992
C309A/S	H		No changes in radioligand binding	Scholl and Wells, 2000

The results were obtained from site-directed mutagenesis studies of the A₁ AR (species; H, human; B, bovine; C, canine).
↵2-a Amino acids are represented in single-letter code with position number shown. The first amino acid is that of the wild-type receptor, with the second residue being that used for substitution.
↵2-b Position on helix, using notation of van Rhee and Jacobson (1996).