Table 2.

Effects of human GLP-1R TM1/N-terminal mutants on agonist-mediated cAMP accumulation

cAMP accumulation data were analyzed using a three-parameter logistic equation to determine pEC₅₀ and E_max values. pEC₅₀ is the negative logarithm of the molar concentration of agonist that induced half the maximal response. E_max for mutants is expressed as a percentage of wildtype. Logτ_c is the operational efficacy value (determined via the Black and Leff operational model (24)), corrected for cell-surface expression of GLP-1R. All values for cAMP accumulation are mean ± S.E. of four to six independent experiments, conducted in duplicate. One-way ANOVA and Dunnett's post-test were used to determine statistical differences (*, p < 0.05). ND, not determined.

	Agonist-mediated cAMP accumulation
	GLP-1(7–36)-NH2			Exendin-4			Oxyntomodulin
	pEC50	E max	Logτc	pEC50	E max	Logτc	pEC50	E max	Logτc
Wildtype	9.84 ± 0.04	97.77 ± 1.13	0.77 ± 0.07	10.43 ± 0.03	99.32 ± 0.90	0.81 ± 0.09	7.99 ± 0.03	98.16 ± 1.13	0.73 ± 0.06
R24A	10.55 ± 0.14*	77.09 ± 2.92*	0.18 ± 0.05*	10.83 ± 0.16	74.16 ± 3.10*	0.13 ± 0.06*	8.52 ± 0.11	81.17 ± 2.99	0.25 ± 0.06
P25A	10.33 ± 0.08	97.02 ± 2.21	0.67 ± 0.10	10.67 ± 0.18	97.12 ± 4.65	0.67 ± 0.10	8.29 ± 0.11	102.90 ± 4.26	0.86 ± 0.18
Q26A	10.20 ± 0.09	92.56 ± 2.61	0.53 ± 0.07	10.56 ± 0.08	97.69 ± 2.24	0.66 ± 0.11	8.31 ± 0.10	109.70 ± 3.98	1.15 ± 0.28
G27A	9.36 ± 0.49	6.91 ± 0.99*	−0.70 ± 0.16*	10.39 ± 0.57	6.62 ± 0.94*	−0.70 ± 0.16*	ND	ND	ND
A28G	10.14 ± 0.10	102.20 ± 3.14	0.84 ± 0.15	10.51 ± 0.12	110.00 ± 3.61	1.22 ± 0.19	8.10 ± 0.07	108.20 ± 3.07	1.13 ± 0.30
T29A	ND	ND	ND	ND	ND	ND	ND	ND	ND
V30A	9.93 ± 0.16	108.20 ± 5.48	1.09 ± 0.14	10.50 ± 0.10	110.50 ± 3.01	1.24 ± 0.22	8.14 ± 0.14	95.92 ± 5.19	0.64 ± 0.11
E128A	9.87 ± 0.39	4.59 ± 0.42*	−0.25 ± 0.14*	10.62 ± 0.72	4.63 ± 0.48*	−0.22 ± 0.25	8.08 ± 0.53	4.15 ± 0.83*	−0.35 ± 0.20*
S129A	9.85 ± 0.10	98.92 ± 3.30	0.83 ± 0.12	10.44 ± 0.09	111.50 ± 2.93	1.45 ± 0.31*	8.10 ± 0.11	87.57 ± 3.84	0.57 ± 0.07
K130A	9.35 ± 0.09	116.20 ± 3.83*	1.47 ± 0.20*	10.05 ± 0.18	77.74 ± 4.44*	0.59 ± 0.05	7.46 ± 0.17	89.78 ± 7.01	0.82 ± 0.10
R131A	10.15 ± 0.21	76.34 ± 4.84*	0.22 ± 0.05*	10.78 ± 0.15	101.40 ± 4.12	0.78 ± 0.14	8.16 ± 0.26	108.70 ± 10.93	1.10 ± 0.22
G132A	9.83 ± 0.16	33.04 ± 1.67*	−0.31 ± 0.06*	10.58 ± 0.25	35.90 ± 2.36*	−0.28 ± 0.06*	8.29 ± 0.12	29.04 ± 1.30*	−0.39 ± 0.06*
E133A	9.74 ± 0.17	87.76 ± 4.92	0.55 ± 0.07	10.09 ± 0.16	103.40 ± 5.28	1.01 ± 0.38	7.90 ± 0.11	110.50 ± 5.20	1.30 ± 0.26*
R134A	9.86 ± 0.12	102.80 ± 4.06	0.80 ± 0.15	10.28 ± 0.17	89.67 ± 4.44	0.48 ± 0.08	7.97 ± 0.10	104.30 ± 4.41	0.87 ± 0.20
S135A	9.72 ± 0.15	114.00 ± 5.30*	1.24 ± 0.11*	9.99 ± 0.09	99.42 ± 2.79	1.11 ± 0.15	7.99 ± 0.11	113.40 ± 5.13	1.03 ± 0.14
S136A	9.42 ± 0.23	96.37 ± 7.34	0.67 ± 0.10	10.00 ± 0.10	81.16 ± 2.54*	0.29 ± 0.05	7.70 ± 0.10	116.20 ± 5.12	1.07 ± 0.33
P137A	9.64 ± 0.12	101.30 ± 3.90	0.82 ± 0.13	10.45 ± 0.29	88.74 ± 7.37	0.50 ± 0.07	7.65 ± 0.20	79.11 ± 6.64	0.32 ± 0.07
E138A	9.63 ± 0.15	94.25 ± 4.49	0.41 ± 0.08	10.46 ± 0.14	112.30 ± 4.24*	1.22 ± 0.18	7.86 ± 0.16	100.40 ± 6.56	0.57 ± 0.13
E139A	10.29 ± 0.19	58.81 ± 3.12*	0.43 ± 0.06	10.90 ± 0.51	28.03 ± 3.75*	−0.08 ± 0.07*	8.16 ± 0.31	34.23 ± 3.94*	0.04 ± 0.06*
Q140A	7.91 ± 0.15*	59.59 ± 5.48*	0.52 ± 0.08	8.68 ± 0.14*	59.75 ± 3.60*	0.45 ± 0.07	6.32 ± 0.18*	63.82 ± 9.80	0.40 ± 0.07
L141A	9.68 ± 0.18	95.20 ± 5.60	0.51 ± 0.09	10.43 ± 0.12	113.20 ± 3.68*	1.42 ± 0.23	7.22 ± 0.18*	106.90 ± 10.38	0.88 ± 0.18
L142A	9.48 ± 0.19	72.12 ± 4.84*	0.24 ± 0.08*	10.79 ± 0.27	76.65 ± 5.75*	0.21 ± 0.05	7.41 ± 0.18	72.94 ± 5.98	0.25 ± 0.08
F143A	10.18 ± 0.13	91.47 ± 3.55	0.56 ± 0.11	10.78 ± 0.21	84.00 ± 4.91*	0.41 ± 0.10	7.96 ± 0.24	91.72 ± 9.10	0.56 ± 0.10
L144A	8.03 ± 0.18*	53.89 ± 5.51*	0.57 ± 0.07	8.90 ± 0.14*	68.52 ± 3.71*	0.75 ± 0.09	ND	ND	ND
Y145A	9.36 ± 0.13	116.40 ± 5.51*	1.44 ± 0.21*	10.00 ± 0.09	109.30 ± 3.28	1.25 ± 0.25	7.57 ± 0.11	103.90 ± 4.88	0.98 ± 0.22
I146A	9.41 ± 0.16	108.30 ± 6.35	1.43 ± 0.18*	10.55 ± 0.21	87.23 ± 5.09	0.78 ± 0.10	7.79 ± 0.27	77.14 ± 8.62	0.59 ± 0.07
I147A	9.34 ± 0.20	80.68 ± 5.54*	0.32 ± 0.05*	10.83 ± 0.39	69.46 ± 7.47*	0.14 ± 0.07*	7.74 ± 0.36	46.61 ± 6.97	0.19 ± 0.07*
Y148A	8.45 ± 0.12*	106.20 ± 6.02	1.08 ± 0.07	9.96 ± 0.29	95.57 ± 9.29	0.84 ± 0.10	5.95 ± 0.50*	173.10 ± 106.70*	0.83 ± 0.27