Crystal structures of Scone: pseudosymmetric folding of a symmetric designer protein.

Recent years have seen an increase in the development of computational proteins, including symmetric ones. A ninefold-symmetric ß-propeller protein named Cake has recently been developed. Here, attempts were made to further engineer this protein into a threefold-symmetric nine-bladed propeller using computational design. Two nine-bladed propeller proteins were designed, named Scone-E and Scone-R. Crystallography, however, revealed the structure of both designs to adopt an eightfold conformation with distorted termini, leading to a pseudo-symmetric protein. One of the proteins could only be crystallized upon the addition of a polyoxometalate, highlighting the usefulness of these molecules as crystallization additives.

A mild post-functionalization method for the vanadium substituted P2W15V3 Wells-Dawson polyoxometalate based on a copper catalyzed azide-alkyne cycloaddition.

A mild post-functionalization method, based on a copper(i) catalyzed azide-alkyne cycloaddition, was developed for the fragile [P2W15V3]9- (PWV). PWV was functionalized with an azide and used as a platform to attach various alkyne functionalized compounds.

Polyoxometalates as artificial nucleases: hydrolytic cleavage of DNA promoted by a highly negatively charged ZrIV-substituted Keggin polyanion.

A highly negatively charged binuclear ZrIV-substituted Keggin polyoxometalate [{α-PW11O39Zr(µ-OH)(H2O)}2]8- (ZrK 2 : 2) has been shown to promote the hydrolytic cleavage of phosphoester bonds in the supercoiled plasmid pUC19 DNA under physiological pH and temperature, giving relaxed and linear forms of pUC19 as hydrolysis products. The interaction between ZrK 2 : 2 and DNA was experimentally proven by circular dichroism (CD) spectroscopy and 31P diffusion ordered NMR spectroscopy.

Following the stability of amphiphilic nanoaggregates by using intermolecular energy transfer.

An intermolecular energy transfer system is developed for studying the stability of nanoaggregate(s) (NAs) in complex solution and cell culture by one- and two-photon fluorescence microscopy and optical imaging. The system allows facile addition of one or more tumor targeting molecules, one of which is exemplified here. NAs functionalized with an MRI and optical probe, with and without folic acid, remain stable in fetal bovine serum for at least 4 hours. HeLa cell cultures showed a clear difference between NAs non-targeted and targeted to folate receptors, with both NAs appearing to be taken up by the cells through different mechanisms. An MRI relaxivity, r1, of 9 mM-1 s-1 at 310 K and 1.4 T was measured associated with the increased rotational correlation time of the NAs. These NAs may have application in the targeted drug delivery of hydrophobic drugs such as doxorubicin (DOX).

Thermodynamic study of the interaction between hen egg white lysozyme and Ce(IV)-Keggin polyoxotungstate as artificial protease.

The molecular interactions of the Keggin polyoxometalate [Me2NH2]10[Ce(PW11O39)2] (1), which promotes selective hydrolysis of hen egg white lysozyme (HEWL) under physiological conditions, were investigated in detail by isothermal titration calorimetry (ITC), (31)P NMR and circular dichroism (CD) spectroscopy. ITC experiments showed that mixing of 1 and HEWL at pH 7.4 and 25 or 37 °C resulted in complexes having 1 : 1 and 2 : 1 POM : HEWL stoichiometries, respectively, and thermodynamic profiles are in agreement with binding in the vicinity of the Trp28-Val29 and Asn44-Arg45 peptide bonds, which were previously shown to undergo selective hydrolysis by 1. Mixing of HEWL with (NH4)4Ce(SO4)4·4H2O salt indicated the absence of any binding accentuating the importance of the polyoxometalate scaffold for selective interaction with the HEWL surface. In contrast, the lacunary Na9[A-α-PW9O34] polyoxometalate showed an increased binding stoichiometry as compared to 1. Increasing the ionic strength resulted in thermodynamic signatures which indicate preservation of the interaction at the Trp28-Val29 site, while interaction at the Asn44-Arg45 appears disrupted due to competition with the salt ions. Decreasing the pH to 4.4 at 37 °C resulted in energetic contributions which suggest that binding at the Trp28-Val29 site is favored, while more pronounced binding at the Asn44-Arg45 site was anticipated when the pH was increased to 9.2. The absence of binding between 1 and α-lactalbumin (α-LA), a protein which is highly isostructural to HEWL but with an overall negative charge, was confirmed at pH 7.4 and 37 °C. The influence of the pH on the binding between 1 and α-LA was investigated, demonstrating that at lower pH values, where α-LA becomes more positively charged, a 1 : 1 interaction with 1 is observed.

Absolute configuration assignment of D3-symmetric lanthanide complexes based on circular dichroism induced by interaction with a chiral probe.

Chiroptical properties and absolute configuration have been correlated for a series of [Ln(oda)3](3-) complexes in aqueous solution (Ln=Pr, Nd, Sm, Eu, Tb, Dy, Ho, Er, or Tm; oda=2,2'-oxydiacetic acid). Addition of the chiral probe L-proline (L-Pro) to a series of the racemic complexes resulted in an excess of the Λ-enantiomer.