CRYSTAL STRUCTURES OF A VARIETY OF CATALYTIC ANTIBODY FABS AT 2.0 Å RESOLUTION. Raymond C. Stevens, Chemistry Department, University of California, Berkeley 94720

Catalytic antibodies were designed to catalyze a variety of different chemical reactions. To date, more than 100 different chemical reactions have been catalyzed with the assistance of antibodies. The catalytic efficiency of these antibodies has varied, but few have had catalytic rates comparable to enzymes. Furthermore, only a few catalytic antibody structures have been determined. Based on the crystallographic investigations described below, a comparison will be made to evaluate similarities and differences between a number of different catalytic antibodies. The structures suggest a number of different modification that can be made to improve the catalytic rates. Furthermore, by studying the mature antibody structures and comparing them to the germline antibody structures, one may be able to learn a great deal about how the immune system increases it's affinity for antigen, and allow one to think differently in the design of catalytic antibodies and hapten.

We have determined the 3-dimensional crystal structure of the 48G7 Fab ester hydrolysis catalytic antibody at 1.9 Å resolution in the presence of hapten, and 2.6 Å in the absence of hapten. Very few changes are observed between the two structures. We are presently refining the structures of the germline constructs of the 48G7 antibody in an effort to understand the antibody maturation process.

A second system under investigation is the sulfide oxidation antibody catalyzed reaction. This Fab structure has been determined at 1.7 Å resolution in the presence of hapten, and 2.2 Å resolution in the absence of hapten. Similar to the ester hydrolysis Fab structure, very few changes are observed between the apo and hapten bound forms. Interestingly, the antibody binding site appears to be primarily an entropic trap for the two substrate molecules that combine to form product. Based on the structure determination, modification of hapten design and antibody mutagenesis are in progress to improve the catalytic efficiency of the antibody reactions.

A third system under investigation is the aminoacylation antibody catalyzed reaction. The structure has been determined at 2.6 Å resolution. Of all of the catalytic antibodies, this antibody is one of the fastest antibody catalyzed reactions to date.