Catalytic Properties of the Antibody H11

A modelling study of a non-concerted hydrolytic cycloaddition reaction by the catalytic antibody H11

H11 is the first antibody reported to have dual activity as a non-concerted, Diels-Alderase and hydrolytic catalyst. It was previously shown to catalyse the cycloaddition of acetoxybutadiene 1a to N-alkyl maleimides 2 to afford hydroxy-substituted bicyclic adducts 3 with a 30% ee of a major isomer. To better understand this mechanism and the partial stereospecificity, a homology model of H11 was constructed and used in docking studies to evaluate potential antibody-ligand complexes. The model suggested the hydrolytic nature of H11 was due to Glu 95H acting as a catalytic base, and evaluation of the shape complementarity of the proposed antibody-ligand complexes confirmed at a semi-quantitative level the observation that the major enantiomer is produced in a 30% ee.

Evolution of shape complementarity and catalytic efficiency from a primordial antibody template

The crystal structure of an efficient Diels-Alder antibody catalyst at 1.9 angstrom resolution reveals almost perfect shape complementarity with its transition state analog. Comparison with highly related progesterone and Diels-Alderase antibodies that arose from the same primordial germ line template shows the relatively subtle mutational steps that were able to evolve both structural complementarity and catalytic efficiency.