Oxo-Replaced Polyoxometalates: There Is More than Oxygen.

The presence of oxo-ligands is one of the main required characteristics for polyoxometalates (POMs), although some oxygen ions in a metallic environment can be replaced by other nonmetals, while maintaining the POM structure. The replacement of oxo-ligands offers a valuable approach to tune the charge distribution and connected properties like reducibility and hydrolytic stability of POMs for the development of tailored compounds. By assessing the reported catalytic and biological applications and connecting them to POM structures, the present review provides a guideline for synthetic approaches and aims to stimulate further applications where the oxo-replaced compounds are superior to their oxo-analogues.

Wells-Dawson phosphotungstates as mushroom tyrosinase inhibitors: a speciation study.

In order to elucidate the active polyoxotungstate (POT) species that inhibit fungal polyphenol oxidase (AbPPO4) in sodium citrate buffer at pH 6.8, four Wells-Dawson phosphotungstates [α/β-PWO] (intact form), [α-PWO] (monolacunary), [PWO] (trilacunary) and [HPWO] (hexalacunary) were investigated. The speciation of the POT solutions under the dopachrome assay (50 mM Na-citrate buffer, pH 6.

Speciation of Transition-Metal-Substituted Keggin-Type Silicotungstates Affected by the Co-crystallization Conditions with Proteinase K.

We report on the synthesis of the tetrasubstituted sandwich-type Keggin silicotungstates as the pure Na salts Na[(A-α-SiWO){Co(OH)(HO)}]·37HO () and Na[(A-α-SiWO){Ni(OH)(HO)}]·77.5HO (), which were prepared by applying a new synthesis protocol and characterized thoroughly in the solid state by single-crystal and powder X-ray diffraction, IR spectroscopy, thermogravimetric analysis, and elemental analysis. Proteinase K was applied as a model protein and the polyoxotungstate (POT)-protein interactions of and were studied side by side with the literature-known KNa[A-α-SiWO(OH){Co(OAc)}]·28.

Transition metal-substituted Keggin polyoxotungstates enabling covalent attachment to proteinase K upon co-crystallization.

The use of α- and β-Keggin polyoxotungstates (POTs) substituted by a single first row transition metal ion (CoII, NiII, CuII, ZnII) as superchaotropic crystallization additives led to covalent and non-covalent interactions with protein side-chains of proteinase K. Two major Keggin POT binding sites in proteinase K were identified, both stabilizing the orientation of the substituted metal site towards the protein surface and suggesting increased protein affinity for the substitution sites. The formation of all observed covalent bonds involves the same aspartate carboxylate, taking the role of a terminal oxygen with the Keggin α-isomer or even, in an unprecedented scenario, a bridging cluster oxygen with the β-isomer.

Keggin-type polyoxotungstates as mushroom tyrosinase inhibitors - A speciation study.

Mushroom tyrosinase abPPO4 is a commercially relevant polyphenol oxidase and has been being targeted for numerous inhibition studies including polyoxometalates (POMs). In the present work, its diphenolase activity was inhibited at pH 6.8 by a series of structurally related polyoxotungstates (POTs) of the α-Keggin archetype, exhibiting the general formula [XWO] in order to elucidate charge-dependent activity correlations.

Successful amphiphiles as the key to crystallization of membrane proteins: Bridging theory and practice.

Background: Membrane proteins constitute a major group of proteins and are of great significance as pharmaceutical targets, but underrepresented in the Protein Data Bank. Particular reasons are their low expression yields and the constant need for cautious and diligent handling in a sufficiently stable hydrophobic environment substituting for the native membrane. When it comes to protein crystallization, such an environment is often established by detergents.

The crystallization additive hexatungstotellurate promotes the crystallization of the HSP70 nucleotide binding domain into two different crystal forms.

The use of the tellurium-centered Anderson-Evans polyoxotungstate [TeW6O24]6- (TEW) as a crystallization additive has been described. Here, we present the use of TEW as an additive in the crystallization screening of the nucleotide binding domain (NBD) of HSP70. Crystallization screening of the HSP70 NBD in the absence of TEW using a standard commercial screen resulted in a single crystal form.

The P-type ATPase inhibiting potential of polyoxotungstates.

Polyoxometalates (POMs) are transition metal complexes that exhibit a broad diversity of structures and properties rendering them promising for biological purposes. POMs are able to inhibit a series of biologically important enzymes, including phosphatases, and thus are able to affect many biochemical processes. In the present study, we analyzed and compared the inhibitory effects of nine different polyoxotungstates (POTs) on two P-type ATPases, Ca-ATPase from skeletal muscle and Na/K-ATPase from basal membrane of skin epithelia.

The polypeptide biophysics of proline/alanine-rich sequences (PAS): Recombinant biopolymers with PEG-like properties.

PAS polypeptides comprise long repetitive sequences of the small L-amino acids proline, alanine and/or serine that were developed to expand the hydrodynamic volume of conjugated pharmaceuticals and prolong their plasma half-life by retarding kidney filtration. Here, we have characterized the polymer properties both of the free polypeptides and in fusion with the biopharmaceutical IL-1Ra. Data from size exclusion chromatography, dynamic light scattering, circular dichroism spectroscopy and quantification of hydrodynamic and polar properties demonstrate that the biosynthetic PAS polypeptides exhibit random coil behavior in aqueous solution astonishingly similar to the chemical polymer poly-ethylene glycol (PEG).

PAS-cal: a generic recombinant peptide calibration standard for mass spectrometry.

We describe the design, preparation, and mass-spectrometric characterization of a new recombinant peptide calibration standard with uniform biophysical and ionization characteristics for mass spectrometry. "PAS-cal" is an artificial polypeptide concatamer of peptide cassettes with varying lengths, each composed of the three small, chemically stable amino acids Pro, Ala, and Ser, which are interspersed by Arg residues to allow site-specific cleavage with trypsin. PAS-cal is expressed at high yields in Escherichia coli as a Small Ubiquitin-like MOdifier (SUMO) fusion protein, which is easily purified and allows isolation of the PAS-cal moiety after SUMO protease cleavage.