Hydrolysis of Peptide Bonds in Protein Micelles Promoted by a Zirconium(IV)-Substituted Polyoxometalate as an Artificial Protease.

The development of artificial proteases is challenging, but important for many applications in modern proteomics and biotechnology. The hydrolysis of hydrophobic or unstructured proteins is particularly difficult due to their poor solubility, which often requires the presence of surfactants. Herein, it is shown that a zirconium(IV)-substituted Keggin polyoxometalate (POM), (Et NH ) [Zr(α-PW O ) ] (1), is able to selectively hydrolyze β-casein, which is an intrinsically unstructured protein at pH 7.

Selective Hydrolysis of Ovalbumin Promoted by Hf(IV)-Substituted Wells-Dawson-Type Polyoxometalate.

The reactivity and selectivity of Wells-Dawson type polyoxometalate (POM), K[Hf(α-PWO)]·19HO (Hf1-WD2), have been examined with respect to the hydrolysis of ovalbumin (OVA), a storage protein consisting of 385 amino acids. The exact cleavage sites have been determined by Edman degradation experiments, which indicated that Hf1-WD2 POM selectively cleaved OVA at eight peptide bonds: Phe13-Asp14, Arg85-Asp86, Asn95-Asp96, Ala139-Asp140, Ser148-Trp149, Ala361-Asp362, Asp362-His363, and Pro364-Phe365. A combination of spectroscopic methods including P NMR, Circular Dichroism (CD), and Tryptophan (Trp) fluorescence spectroscopy were employed to gain better understanding of the observed selective cleavage and the underlying hydrolytic mechanism.

Selectivity and Reactivity of Zr and Ce Substituted Keggin Type Polyoxometalates Toward Cytochrome c in Surfactant Solutions.

In this paper we investigate the effect of three different types of surfactants, on the hydrolysis of Cytochrome c (Cyt c), a predominantly α helical protein containing a heme group, promoted by [Ce(α PW)2]10- (CeK) and [Zr(α PW)2]10- (ZrK) polyoxometalates. In the presence of SDS, Zw3 12, or CHAPS surfactants, which are commonly used for solubilizing hydrophobic proteins, the specificity of CeK or ZrK toward hydrolysis of Cyt c does not change. However, the hydrolysis rate of Cyt c by CeK was increased in the presence of SDS, but decreased in the presence of CHAPS, and was nearly inhibited in the presence of Zw3 12.

A Simple Nucleophilic Substitution as a Versatile Postfunctionalization Method for the Coupling of Nucleophiles to an Anderson-Type Polyoxometalate.

A new postfunctionalization method was developed for the Anderson-type POM based on a nucleophilic substitution reaction occurring at an electrophilic sp hybridized carbon localized on the hybrid POM. Using this method, several types of different nucleophiles including primary and secondary amines, carboxylates, and thiolates were efficiently coupled to a chloride-functionalized Anderson-type POM in high yields and purity. The heterogeneous acetonitrile-NaCO conditions were found to be superior over other bases and solvents for the coupling of amines and thiolates to the chloride-functionalized POM.

Interaction Study and Reactivity of Zr(IV) -Substituted Wells-Dawson Polyoxometalate towards Hydrolysis of Peptide Bonds in Surfactant Solutions.

The interaction between the 1:2 Zr(IV) :Wells-Dawson complex, K15 H[Zr(α2 -P2 W17 O61 )2] (1), and a range of surfactants was studied in detail with the aim of developing metal-substituted POMs as potential artificial proteases for membrane proteins. The surfactants include the positively charged cetyl(trimethyl)ammonium bromide (CTAB), the negatively charged sodium dodecyl sulfate (SDS), the neutral Triton X-100 (TX-100), and zwitterionic 3-[dodecyl(dimethyl)ammonio]-1-propanesulfonate (Zw3-13) and 3-[dimethyl(3-{[(3α,5β,7α,12α)-3,7,12-trihydroxy-24-oxocholan-24-yl]amino}propyl)ammonio]-1-propanesulfonate (CHAPS). A combination of multinuclear (1)H, (13)C, and (31) P NMR spectroscopy, (1)H diffusion-ordered NMR spectroscopy ((1)H DOSY), and nuclear Overhauser effect spectroscopy (NOESY) was used to examine the interaction between 1 and each surfactant on the molecular level.