Canonical binding arrays as molecular recognition elements in the immune system: tetrahedral anions and the ester hydrolysis transition state

The structures, obtained by X-ray crystallography, of the binding sites of catalytic antibodies raised to bind different phosphonates are compared. Although the amino acid sequences differ, all exhibit a tetrahedral array of hydrogen bond donors (a ‘canonical binding array’) complementary to the tetrahedral anion, which represents a ‘transition state epitope’ for the basic hydrolysis of esters and amides. Antibodies for phosphates, arsonates, and sulfonates are found also to possess the tetrahedral anion canonical binding array.