Highly selective and sensitive macrocycle-based dinuclear foldamer for fluorometric and colorimetric sensing of citrate in water.

The selective detection of citrate anions is essential for various biological functions in living systems. A quantitative assessment of citrate is required for the diagnosis of various diseases in the human body; however, it is extremely challenging to develop efficient fluorescence and color-detecting molecular probes for sensing citrate in water. Herein, we report a macrocycle-based dinuclear foldamer (1) assembled with eosin Y (EY) that has been studied for anion binding by fluorescence and colorimetric techniques in water at neutral pH. Results from the fluorescence titrations reveal that the 1·EY ensemble strongly binds citrate anions, showing remarkable selectivity over a wide range of inorganic and carboxylate anions. The addition of citrate anions to the 1·EY adduct led to a large fluorescence enhancement, displaying a detectable color change under both visible and UV light in water up to 2 μmol. The biocompatibility of 1·EY as an intracellular carrier in a biological system was evaluated on primary human foreskin fibroblast (HF) cells, showing an excellent cell viability. The strong binding properties of the ensemble allow it to be used as a highly sensitive, detective probe for biologically relevant citrate anions in various applications

Anion receptor chemistry: highlights from 2011 and 2012

This review covers advances in anion complexation in the years 2011 and 2012. The review covers both organic and inorganic systems and also highlights the applications to which anion receptors can be applied such as self-assembly and molecular architecture, sensing, catalysis and anion transport

Interaction of anticancer reduced Schiff base coumarin derivatives with human serum albumin investigated by fluorescence quenching and molecular modeling

The specific binding of five reduced Schiff base derived 7-amino-coumarin compounds with antitumor activity to human serum albumin, the principal binding protein of blood, was studied by fluorescence spectroscopy. Their conditional binding constants were computed and the reversible binding at the Sudlow’s site I was found to be strong (KD ~ 0.03-2.09 M). Based on the data albumin can provide a depot for the compounds and is responsible for their biodistribution and transport processes. The experimental data is complemented by protein– ligand docking calculations for two representatives which support the observations. The proton dissociation constants of the compounds were also determined by UV-Vis spectrophotometric and fluorometric titrations to obtain the actual charges and distribution of the species in the various protonation states at physiological pH

Analysis of the interaction of calcitriol with the disulfide isomerase ERp57

Calcitriol, the active form of vitamin D3, can regulate the gene expression through the binding to the nuclear receptor VDR, but it can also display nongenomic actions, acting through a membrane- associated receptor, which has been discovered as the disul de isomerase ERp57. The aim of our research is to identify the binding sites for calcitriol in ERp57 and to analyze their interaction. We rst studied the interaction through bioinformatics and uorimetric analyses. Subsequently, we focused on two protein mutants containing the predicted interaction domains with calcitriol: abb’- ERp57, containing the rst three domains, and a’-ERp57, the fourth domain only. To consolidate the achievements we used the calorimetric approach to the whole protein and its mutants. Our results allow us to hypothesize that the interaction with the a’ domain contributes to a greater extent than the other potential binding sites to the dissociation constant, calculated as a Kd of about 10−9 M

Distinct ubiquitin binding modes exhibited by SH3 domains: Molecular determinants and functional implications

SH3 domains constitute a new type of ubiquitin-binding domains. We previously showed that the third SH3 domain (SH3-C) of CD2AP binds ubiquitin in an alternative orientation. We have determined the structure of the complex between first CD2AP SH3 domain and ubiquitin and performed a structural and mutational analysis to decipher the determinants of the SH3-C binding mode to ubiquitin. We found that the Phe-to-Tyr mutation in CD2AP and in the homologous CIN85 SH3-C domain does not abrogate ubiquitin binding, in contrast to previous hypothesis and our findings for the first two CD2AP SH3 domains. The similar alternative binding mode of the SH3-C domains of these related adaptor proteins is characterised by a higher affinity to C-terminal extended ubiquitin molecules. We conclude that CD2AP/CIN85 SH3-C domain interaction with ubiquitin constitutes a new ubiquitin-binding mode involved in a different cellular function and thus changes the previously established mechanism of EGF-dependent CD2AP/CIN85 mono-ubiquitination. © 2013 Ortega Roldan et al

Imaging and energetics of single SSB-ssDNA molecules reveal intramolecular condensation and insight into RecOR function.

Escherichia coli single-stranded DNA (ssDNA) binding protein (SSB) is the defining bacterial member of ssDNA binding proteins essential for DNA maintenance. SSB binds ssDNA with a variable footprint of ∼30-70 nucleotides, reflecting partial or full wrapping of ssDNA around a tetramer of SSB. We directly imaged single molecules of SSB-coated ssDNA using total internal reflection fluorescence (TIRF) microscopy and observed intramolecular condensation of nucleoprotein complexes exceeding expectations based on simple wrapping transitions. We further examined this unexpected property by single-molecule force spectroscopy using magnetic tweezers. In conditions favoring complete wrapping, SSB engages in long-range reversible intramolecular interactions resulting in condensation of the SSB-ssDNA complex. RecO and RecOR, which interact with SSB, further condensed the complex. Our data support the idea that RecOR--and possibly other SSB-interacting proteins-function(s) in part to alter long-range, macroscopic interactions between or throughout nucleoprotein complexes by microscopically altering wrapping and bridging distant sites

Kinetic and mechanistic studies on aldehyde dehydrogenases from sheep liver : a thesis presented in partial fulfilment of the requirements for the degree of Master of Science in Chemistry at Massey University, New Zealand

The mechanisms of sheep liver aldehyde dehydrogenases have been further investigated by both steady-state and pre-steady-state kinetic methods. By utilizing the acid/base indicator phenol red, a burst in the production of protons has been detected for both the cytoplasmic and mitochondrial isoenzymes. The rates and amplitudes of the two proton bursts were almost identical to those for the NADH bursts which both isoenzymes exhibit. After a consideration of the kinetic data, the electronic structure of various aldehydes and computer simulation studies, the proton burst process was postulated as arising from a conformational change on aldehyde binding to the enzyme-NAD + binary complex. The proton release arises from the perturbation of the pKa of a protonated functional group from about 8.5 to below 5.0 The effects of the Mg 2+ ion on the cytoplasmic isoenzyme were also studied. The presence of millimolar concentrations of this ion resulted in marked inhibition of the enzyme activity, and a lowering of the dissociation constants for both the E.NAD + and E.NADH binary-enzyme complexes. Steady-state and pre-steady-state studies showed that the major effect of MgCl 2 on the enzyme mechanism was to slow the steady-state rate-limiting step, which was NADH dissociation at high propionaldehyde concentrations and an unidentified step, possibly involving deacylation, at low propionaldehyde concentrations

A modular self-assembled sensing system for heavy metal ions with tunable sensitivity and selectivity

Here we describe a self-assembled sensing system composed of three separate modules: gold nano particles, a reporter element, and a recognition element. The gold nanoparticles serve as a multivalent platform for the interaction with both the reporter and recognition element and the gold nucleus serves to affect the fluorescent properties of the reporter. The reporter element serves for generation of the output signal. The recognition element serves to make the assay selective. The working principle is that the interaction of the analyte with the recognition element leads to an increased affinity for the gold nanoparticle, which causes a displacement of the reporter and a turn-ON of fluorescence. It is shown that the modular nature of the system permits straightforward tuning of the dynamic detection range, the sensitivity, and the selectivity, simply by changing the recognition module. The system can detect Hg2+ and Ag+ metal ions at nanomolar concentrations in aqueous buffer

Sensing a Bacillis anthracis biomarker with well-known OLED emitter EuTta3Phen

Dipicolinic acid (DPA) is a distinctive biomarker for bacterial spores. Here, we present the successful demonstration of dramatic Switch-OFF sensing of DPA using an easily synthesised Eu(III) phosphor applied primarily in light-emitting devices. The sensor in the presence of water and phosphate is also demonstrated to be effective