Surface charge fit, peptide bond snip: Metal-substituted polyoxometalates as region selective artificial proteases

The total number of different proteins present in Earth organisms is estimated to be up to 10 million. While their identification in terms of primary sequence is expanding at an increasing rate, elucidation of their function and structure is drastically lacking behind. Due to their large size, hydrolysis of proteins into more manageable fragments is a frequently required procedure in biochemical practice. However, the natural enzymes and chemical agents that are currently used for protein hydrolysis have several drawbacks and only few of them are selective. This has inspired many research groups to design new artificial proteases, with a recent focus on metal-containing complexes.[1] Our research group combines the use of strong Lewis acid metal cations with polyoxometalate (POM) ligands, which are known to specifically interact with proteins.[2] Different POMs containing Zr(IV) or Ce(IV) were synthesized and characterized by NMR spectroscopy. A range of different dipeptides and proteins were successfully hydrolyzed at pH 7.4. In the case of dipeptide targets, the reactions were followed by NMR spectroscopy in order to obtain a full kinetic reaction profile.[3] Cleavage sites in larger protein targets were determined by SDS-PAGE and subsequent Edman degradation and the interaction at the respective sites was studied by CD, NMR spectroscopy and ITC.[4] The reaction and interaction studies show that the hydrolytic reactivity originates from the incorporated metal ion, while binding to the target is achieved via POM-protein interactions. The general importance of electrostatic contacts in driving the reactivity was further confirmed by hydrolysis experiments at different pH and ionic strength. [1] K. B. Grant and M. Kassai, Current Organic Chemistry 2006, 10, 1035-1049. [2] G. J. Zhang, B. Keita, C. T. Craescu, S. Miron, P. de Oliveira and L. Nadjo, Biomacromolecules 2008, 9, 812-817. [3] G. Absillis and T. N. Parac-Vogt, Inorganic Chemistry 2012, 51, 9902-9910. [4] K. Stroobants, E. Moelants, H. G. T. Ly, P. Proost, K. Bartik and T. N. Parac-Vogt, Chemistry-a European Journal 2013, 19, 2848-2858.status: publishe