Table 2.

Ligand binding data^a

Mutant	GA88	GA95	GA98	GB98	GB98-T25I	GB98-T25I,L20A
Fold	3α	3α	3α	4β+α	3α (95%) 4β+α (5%)	4β+α
KD(HSA)	37 (31)b	30	244	n.b.	n.b.	n.b.
KD(IgG)	n.b.	n.b.	62	<1c	15	<1c

^aDissociation constants are in micromolar units. The experimental error is estimated to be ±30%. All binding measurements were done at 15°C except those for G_B98-T25I, which were done at 5°C. n.b., no binding detected.

^bValue in parentheses is from isothermal titration calorimetry (see also Figure S3).

^cAll G_B protein was bound even at the lowest IgG concentrations used.