A COMPARISON OF THE CRYSTALLOGRAPHIC STRUCTURES OF 2 CATALYTIC ANTIBODIES WITH ESTERASE-ACTIVITY

The crystallographic structure of the Fab fragment of the catalytic an tibody, 29G11, complexed with an (S)-norleucine phenyl phosphonate tra nsition state analog was determined at 2.2 Angstrom resolution. The an tibody catalyzes the hydrolysis of norleucine phenyl ester with(S)-ena ntioselectivity. The shape and charge complementarity of the binding p ocket for the hapten account for the preferential binding of the (S)-e nantiomer of the substrate. The structure is compared to that of the m ore catalytically efficient antibody, 17E8, induced by the same hapten transition state analog. 29G11 has different residues from 17E8 at ei ght positions in the heavy chain, including four substitutions in the hapten-binding pocket: A33V, S95G, S99R and Y100(A)N, and four substit utions at positions remote from the catalytic site, I28T, R40K, V65G a nd F91L. The two antibodies show large differences in the orientations of their variable and constant domains, reflected by a 32 degrees dif ference in their elbow angles. The V-L and V-H domains in the two anti bodies differ by a rotation of 8.8 degrees. The hapten binds in simila r orientations and locations in 29G11 and 17E8, which appear to have c atalytic groups in common, though the changes in the association of th e variable domains affect the precise positioning of residues in the h apten-binding pocket. (C) 1998 Academic Press.