A collaborative project is underway with the Schultz laboratory to probe the structure and function of catalytic antibodies. Allowing the immune system to evolve a catalyst for unique chemical reactions can prove both useful from a practical standpoint and may provide insight into how biomolecules evolve their structure to optimize function (i.e., enzyme catalysis and molecular recognition). Using the techniques of protein crystallography and site-directed mutagenesis, we are examining the three-dimensional structures of both germline and mature catalytic antibodies to understand how antibody catalysis evolves and how we can improve the catalytic efficiency of these molecules.
The immune system produces high-affinity, selective receptors by screening a large library of antibody combining sites. Diversity is generated from the combinatorial association of variable (V), diversity (D), and joining (J) segments, followed by somatic hypermutation of the germline antibody genes to optimize antibody-antigen recognition. By harnessing this natural combinatorial process, chemists have generated catalytic antibodies with specificities, and in some cases rates, rivaling those of enzymes. Moreover, antibodies have been generated that catalyze a broad array of reactions, including those that are difficult to carry out using existing chemical methods, and reactions for which enzymes are not yet known.
Further improvements in the scope of efficiency of antibody catalysis will likely result from high-resolution structural studies of the molecular interactions occurring in the combining site. Such studies will allow us to analyze the relationship between active site geometry, hapten structure, and catalytic efficiency at the atomic level. This analysis should provide a basis for optimizing antibody activity through both directed mutagenesis and improvements in hapten design. The structural characterization of a family of related catalytic antibodies, including the germline precursors and antibody siblings, should also provide new insights into the mechanisms and evolution of biological catalysts as well as the affinity maturation process itself.
Structural Studies by Crystal X-ray Diffraction:
To date, the following structural studies are being actively pursued in this laboratory:Affinity Maturation of Catalytic Antibodies
The crystal structures of a germline antibody Fab fragment and its complex with hapten have been compared with the corresponding crystal structures of the affinity matured antibody.