EMBM - a new enzyme mechanism-based method for rational design of chemical sites of covalent inhibitors.

We introduce an enzyme mechanism-based method (EMBM) aimed at rational design of chemical sites (CS) of reaction coordinate analog inhibitors. The energy of valence reorganization of CS, caused by the formation of the enzyme-inhibitor covalent complex, is accounted for by new covalent descriptors W1 and W2. We considered CS fragments with a carbonyl reactivity center, like in native protease substrates. The W1 and W2 descriptors are calculated quantum mechanically on small molecular clusters simulating the reaction core of the formed covalent tetrahedral complex, anionic TC(O-) or neutral TC(OH). The modeling on a reaction core allows generation of various CS and corresponding TC(O-) and TC(OH) as universal building blocks of real inhibitors and their covalent complexes with serine or cysteine hydrolases. Moreover, the approach avoids the need for 3D structure of the target enzyme, so EMBM may be used for ligand-based design. We have built a chemical site of inhibitors (CSI) databank with pairs of W1 and W2 descriptors precalculated for both CH₃O(-) and CH₃S(-) nucleophiles for every collected CS fragment. We demonstrated that contribution of a CS fragment to the binding affinity of an inhibitor depends on both its covalent reorganization during the chemical transformation and its noncovalent interactions in the enzyme active site. Consequently, prediction of inhibitors binding trend can be done only by accounting for all of these factors, using W1 and W2 in combination with noncovalent QSAR descriptors.