Discovery of a novel ligand that modulates the protein–protein interactions of the AAA+ superfamily oncoprotein reptin

Developing approaches to discover protein–protein interactions (PPIs) remains a fundamental challenge. A chemical biology platform is applied here to identify novel PPIs for the AAA+ superfamily oncoprotein reptin. An in silico screen coupled with chemical optimization provided Liddean, a nucleotide-mimetic which modulates reptin''s oligomerization status, protein-binding activity and global conformation. Combinatorial peptide phage library screening of Liddean-bound reptin with next generation sequencing identified interaction motifs including a novel reptin docking site on the p53 tumor suppressor protein. Proximity ligation assays demonstrated that endogenous reptin forms a predominantly cytoplasmic complex with its paralog pontin in cancer cells and Liddean promotes a shift of this complex to the nucleus. An emerging view of PPIs in higher eukaryotes is that they occur through a striking diversity of linear peptide motifs. The discovery of a compound that alters reptin''s protein interaction landscape potentially leads to novel avenues for therapeutic development.     

Luminescence and upconversion from thulium(iii) species in solution

Thulium salts and complexes are shown to be emissive from three states in the excited state manifold of Tm(3+). Formation of the (1)D(2) state can result in luminescence, or in energy transfer to the lower energy (1)G(4) and (3)H(4) emissive states. Where chromophores are present in the ligand structure, emission is restricted to thulium centred emissive states that are lower in energy than the chromophore centred donor state. We have also observed direct multi-photon excitation of the thulium excited state manifold. Furthermore, additional transitions are observed in the multi-photon excitation spectra that are consistent with upconversion as a consequence of sequential single photon absorption and relaxation processes within the thulium excited state manifold.     

Stereochemistry of Molecular Figures-of-Eight

A trans isomer of a figure-of-eight (Fo8) compound was prepared from an electron-withdrawing cyclobis(paraquat-p-phenylene) derivative carrying trans-disposed azide functions between its two phenylene rings. Copper(I)-catalyzed azide-alkyne cycloadditions with a bispropargyl derivative of a polyether chain, interrupted in its midriff by an electron-donating 1,5-dioxynaphthalene unit acting as the template to organize the reactants prior to the onset of two click reactions, afforded the Fo8 compound with C(i) symmetry. Exactly the same chemistry is performed on the cis-bisazide of the tetracationic cyclophane to give a Fo8 compound with C(2) symmetry. Both of these Fo8 compounds exist as major and very minor conformational isomers in solution. The major conformation in the trans series, which has been characterized by X-ray crystallography, adopts a geometry which maximizes its C?H???O interactions, while maintaining its π???π stacking and C?H???π interactions. Ab initio calculations at the M06L level support the conformational assignments to the major and minor isomers in the trans series. Dynamic (1) H?NMR spectroscopy, supported by 2D (1) H?NMR experiments, indicates that the major and minor isomers in both the cis and trans series equilibrate in solution on the (1) H?NMR timescale rapidly above and slowly below room temperature.     

Chiral phosphoproline-catalyzed asymmetric Michael addition of ketones to nitroolefins: an experimental and theoretical study

A novel pyrrolidine-based chiral phosphoproline is an effective bifunctional organocatalyst for the asymmetric Michael addition of ketones to nitroolefins giving high levels of diastereo- and enantio-selectivities (up to > 99 : 1 dr and 96% ee). anti-SR Transition state has the lowest barrier which controls the stereoselectivity, in agreement with experimental results.     

Spectroscopic and redox properties of amine-functionalized K2[OsII(bpy)(CN)4] complexes

We report the first examples of amine-functionalized K(2)[Os(II)(bpy)(CN)(4)] (bpy = 2,2'-bipyridine) complexes. The tetracyanoosmate complexes were prepared by UV irradiation (λ = 254 nm) of K(4)[Os(II)(CN)(6)] and primary amine-functionalized bpy ligands in acidic aqueous media. The aqueous solution pH dependences of the spectroscopic and redox properties of 4,4'- and 5,5'-substituted complexes have been investigated. The pendant amine functional groups and coordinated cyanide ligands are basic sites that can be sequentially protonated, thereby allowing systematic tuning of electrochemical and optical spectroscopic properties.     

Attenuated total reflectance Fourier-transform Infrared spectroscopy analysis of crystallinity changes in lyocell following continuous treatment with sodium hydroxide

Cellulose is a linear 1,4-β-glucan polymer where the units are able to form highly ordered structures, as a result of extensive interaction through intra- and intermolecular hydrogen bonding of the three hydroxyl groups in each cellulose unit. Alkali has a substantial influence on morphological, molecular and supramolecular properties of cellulose II polymer fibres causing changes in crystallinity. These physical changes were observed herein using ATR-FTIR spectroscopy, following continuous treatment of the cellulose II fabrics with aqueous sodium hydroxide solution under varying condition parameters. Post-treatment, maxima for total crystallinity index and lateral order index, and minima for hydrogen bond intensity, were observed at concentrations of 3.3 and 4.5 mol dm⁻³ NaOH, when treated at 25 °C and 40 °C, respectively. Under these treatment conditions, it is proposed that maximum molecular reorganisation occurs in the amorphous and quasi-crystalline phases of the cellulose II polymer.     

Prioritization of charge over geometry in transition state analogues of a dual specificity protein kinase

The direct observation of a transition state analogue (TSA) complex for tyrosine phosphorylation by a signaling kinase has been achieved using (19)F NMR analysis of MEK6 in complex with tetrafluoroaluminate (AlF(4)(-)), ADP, and p38α MAP kinase (acceptor residue: Tyr182). Solvent-induced isotope shifts and chemical shifts for the AlF(4)(-) moiety indicate that two fluorine atoms are coordinated by the two catalytic magnesium ions of the kinase active site, while the two remaining fluorides are liganded by protein residues only. An equivalent, yet distinct, AlF(4)(-) complex involving the alternative acceptor residue in p38α (Thr180) is only observed when the Tyr182 is mutated to phenylalanine. The formation of octahedral AlF(4)(-) species for both acceptor residues, rather than the trigonal bipyramidal AlF(3)(0) previously identified in the only other metal fluoride complex with a protein kinase, shows the requirement of MEK6 for a TSA that is isoelectronic with the migrating phosphoryl group. This requirement has hitherto only been demonstrated for proteins having a single catalytic magnesium ion.     

A Hapten for the Generation of Antibody Phosphatases

Abstract

A series of hydroxymethylene and α,β-unsaturated aminophosphinic acids was prepared, modelled on the ‘exploded’ transition state proposed (Herschlag [1]) for the chemical hydrolysis of phosphate monoesters. They exhibit the dual utility of being transition state analogues for the chemical hydrolysis of phosphate monoesters and having the potential for inhibition of phosphatase enzymes. (1) was chosen to be utilised as a hapten molecule for the generation of catalytic antibodies.