TABLE 3.

Binding properties of LT and CTB mutants

Mutant	GM1 bindinga		Blood sugar bindingc		E. coli surface bindingd
	%	P valueb	%	P value	%	P value
LT[L25E]	69.3 ± 5.3e	<0.005	64.2 ± 7.2	<0.01	35.2 ± 10.9	<0.005
LT[Q3K]f	96.0 ± 4.6	0.43	0.67 ± 0.43	<0.005	33.8 ± 8.8	<0.005
LT[Q3A]	95.5 ± 14.4	0.77	4.0 ± 4.0	2.3 × 10−6	36.5 ± 4.7	<0.0005
LT[E11K]	90.9 ± 4.6	0.08	109.6 ± 17.8	0.65	19.6 ± 9.3	<0.001
LT[E11A]	81.5 ± 6.5	0.07
CTB[Q3K]	93.1 ± 1.9	<0.05
CTB[E11K]	94.7 ± 2.5	0.08
CTB[E11A]	106.7 ± 1.8	<0.05

^aPurified toxin binding to G_M1 was determined by ELISA; values are expressed as mean percentages of wild-type LT or CTB binding ±SEM (n ≥ 3).

^bP values are for comparison to wild-type binding as determined by Student's t test.

^cPurified toxin binding to blood group A trisaccharide conjugated to BSA was determined by ELISA; values are expressed as mean percentages of wild-type binding ±SEM (n ≥ 2).

^dPurified toxin binding to the surface of DH5α E. coli cells was determined by a previously described immunoblot-based binding assay (26); values are expressed as mean percentages of wild-type LT binding ±SEM (n ≥ 3).

^eSignificant differences from wild-type (P < 0.05) are in bold.

^fData for this mutant were reported previously (26).