Mechanistic study of the hydrolytic reactivity of polyoxometalate complexes towards proteins

Structure and function determination of proteins is of major importancein order to understand the functioning of organisms as well as their malfunction resulting in disease. Many biomedical and biochemical approaches for the study of proteins require their fragmentation and only few reagents are available for this purpose. As an alternative of natural proteases, the use of metal complexes for protein hydrolysis has been proposed and has become an increasingly important area of research during the past decade. Since lack of selectivity is the major shortcomingof the currently suggested metal complexes, our group proposes the use of negatively charged oxoanions/polyoxometalates and their metal clusters, which can specifically interact with positive protein patches. The hydrolytic activity of these oxoanions and polyoxometalates towards di- and oligopeptides was previously demonstrated and the first evidence for their reactivity towards protein substrates is reported in the present study.Hydrolysis of proteins such as hen egg white lysozyme (HEWL) andhuman serum albumin (HSA) by oxoanions and polyoxometalates (POMs) was studied. In addition to selectivity studies, kinetic experiments have shown considerable rate enhancements as compared to the uncatalyzed reactions. The cleavage sites for hydrolysis by different complexes were identified and sequence selective hydrolysis in the presence of the oxoanion molybdate versus regioselective hydrolysis in the case of metal-substituted polyoxotungstates was demonstrated. A multi-technique approach was used to study the interaction between POMs and selected proteins, and these studies have shown that electrostatic interactions with the POM are dominant, but that imbedded metal cations can also play an important rolein the binding which precedes the reaction. Studies towards smaller substrates have provided evidence for an Asp side chain assistance mechanism in the presence of molybdate and have proven the applicability of Diffusion Ordered Spectroscopy (DOSY) as a novel technique for the study of oligopeptide hydrolysis in the presence of polyoxotungstates.<w:latentstyles deflockedstate="false" defunhidewhenused="true"