B23-Circular Dichroism
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Diamond Proposal Number(s):
[20210, 21575]
Abstract: The eye lens is a biconvex structure composed of lens fibres, cells that lack of blood and nerve supply and of any organelle, allowing for a high concentration of water soluble proteins that determine the lens transparency and refractive index. The lens water soluble protein pool in mammals is composed of α‐, β‐, and γ‐crystallins, the latter being involved in calcium homeostasis and having structural importance, the first playing a crucial role in preventing protein aggregation and the consequent lens obfuscation, which leads to the clinical outcome of cataract. Among different factors, oxidative stress, free radicals, and reactive oxygen species (ROSs) generated by the exposure to UV light are widely recognized to cause cataract formation. Taking advantage of synchrotron radiation circular dichroism, fluorescence, and circular dichroism spectroscopies, in the present study we investigate the influence of different small molecules with the potential to either quench ROS generation or to stabilize protein conformation. Therefore, ascorbic acid, an excellent antioxidant agent already present in the eye aqueous humour, has been tested along with ceftriaxone, mannitol and trehalose, which osmolyte activity was demonstrated interfering with model proteins misfolding. Our results showed that ascorbic acid strongly inhibits the ROS production without, however, preserving the native protein structure, whereas mannitol had no effect on the ROS production but retained better the secondary structure of WS proteins. Collectively, the use of a mixture of ascorbic acid and mannitol could be used to better protect eye lens proteins from ROS damage preventing the cataract onset.
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Mar 2020
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B23-Circular Dichroism
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Open Access
Abstract: Light-harvesting complex II (LHCII) from the marine green macroalga Bryopsis corticulans is spectroscopically characterized to understand the structural and functional changes resulting from adaptation to intertidal environment. LHCII is homologous to its counterpart in land plants but has a different carotenoid and chlorophyll (Chl) composition. This is reflected in the steady-state absorption, fluorescence, linear dichroism, circular dichroism and anisotropic circular dichroism spectra. Time-resolved fluorescence and two-dimensional electronic spectroscopy were used to investigate the consequences of this adaptive change in the pigment composition on the excited-state dynamics. The complex contains additional Chl b spectral forms – absorbing at around 650 nm and 658 nm – and lacks the red-most Chl a forms compared with higher-plant LHCII. Similar to plant LHCII, energy transfer between Chls occurs on timescales from under hundred fs (mainly from Chl b to Chl a) to several picoseconds (mainly between Chl a pools). However, the presence of long-lived, weakly coupled Chl b and Chl a states leads to slower exciton equilibration in LHCII from B. corticulans. The finding demonstrates a trade-off between the enhanced absorption of blue-green light and the excitation migration time. However, the adaptive change does not result in a significant drop in the overall photochemical efficiency of Photosystem II. These results show that LHCII is a robust adaptable system whose spectral properties can be tuned to the environment for optimal light harvesting.
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Mar 2020
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B23-Circular Dichroism
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Diamond Proposal Number(s):
[8034, 20210]
Open Access
Abstract: The eye lens is mainly composed of the highly ordered water-soluble (WS) proteins named crystallins. The aggregation and insolubilization of these proteins lead to progressive lens opacification until cataract onset. Although this is a well-known disease, the mechanism of eye lens protein aggregation is not well understood; however, one of the recognized causes of proteins modification is related to the exposure to UV light. For this reason, the spectroscopic properties of WS lens proteins and their stability to UV irradiation have been evaluated by different biophysical methods including synchrotron radiation circular dichroism, fluorescence, and circular dichroism spectroscopies. Moreover, dynamic light scattering, gel electrophoresis, transmission electron microscopy, and protein digestion followed by tandem LC–MS/MS analysis were used to study the morphological and structural changes in protein aggregates induced by exposure to UV light. Our results clearly indicated that the exposure to UV radiation modified the protein conformation, inducing a loss of ordered structure and aggregation. Furthermore, we confirmed that these changes were attributable to the generation of reactive oxygen species due to the irradiation of the protein sample. This approach, involving the photodenaturation of proteins, provides a benchmark in high-throughput screening of small molecules suitable to prevent protein denaturation and aggregation.
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Feb 2020
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B23-Circular Dichroism
I19-Small Molecule Single Crystal Diffraction
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Zongsu
Han
,
Kunyu
Wang
,
Yifan
Guo
,
Wenjie
Chen
,
Jiale
Zhang
,
Xinran
Zhang
,
Giuliano
Siligardi
,
Sihai
Yang
,
Zhen
Zhou
,
Pingchuan
Sun
,
Wei
Shi
,
Peng
Cheng
Diamond Proposal Number(s):
[20293]
Open Access
Abstract: The integration of luminescence and chirality in easy-scalable metal-organic frameworks gives rise to the development of advanced luminescent sensors. To date, the synthesis of chiral metal-organic frameworks is poorly predictable and their chirality primarily originates from components that constitute the frameworks. By contrast, the introduction of chirality into the pores of metal-organic frameworks has not been explored to the best of our knowledge. Here, we demonstrate that chirality can be introduced into an anionic Zn-based metal-organic framework via simple cation exchange, yielding dual luminescent centers comprised of the ligand and Tb3+ ions, accompanied by a chiral center in the pores. This bifunctional material shows enantioselectivity luminescent sensing for a mixture of stereoisomers, demonstrated for Cinchonine and Cinchonidine epimers and amino alcohol enantiomers, from which the quantitative determination of the stereoisomeric excess has been obtained. This study paves a pathway for the design of multifunctional metal-organic framework systems as a useful method for rapid sensing of chiral molecules.
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Nov 2019
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B23-Circular Dichroism
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Diamond Proposal Number(s):
[12182, 14484, 16778, 19680]
Abstract: CD spectroscopy is the essential tool to quickly ascertain in the far-UV region the global conformational changes, the secondary structure content, and protein folding and in the near-UV region the local tertiary structure changes probed by the local environment of the aromatic side chains, prosthetic groups (hemes, flavones, carotenoids), the dihedral angle of disulfide bonds, and the ligand chromophore moieties, the latter occurring as a result of protein–ligand binding interaction. Qualitative and quantitative investigations into ligand-binding interactions in both the far- and near-UV regions using CD spectroscopy provide unique and direct information whether induced conformational changes upon ligand binding occur and of what nature that are unattainable with other techniques such as fluorescence, ITC, SPR, and AUC.
This chapter provides an overview of how to perform circular dichroism (CD) experiments, detailing methods, hints and tips for successful CD measurements. Descriptions of different experimental designs are discussed using CD to investigate ligand-binding interactions. This includes standard qualitative CD measurements conducted in both single-measurement mode and high-throughput 96-well plate mode, CD titrations, and UV protein denaturation assays with and without ligand.
The highly collimated micro-beam available at B23 beamline for synchrotron radiation circular dichroism (SRCD) at Diamond Light Source (DLS) offers many advantages to benchtop instruments. The synchrotron light source is ten times brighter than a standard xenon arc light source of benchtop instruments. The small diameter of the synchrotron beam can be up to 160 times smaller than that of benchtop light beams; this has enabled the use of small aperture cuvette cells and flat capillary tubes reducing substantially the amount of volume sample to be investigated. Methods, hints and tips, and golden rules to measure good quality, artifact-free SRCD and CD data will be described in this chapter in particular for the study of protein–ligand interactions and protein photostability.
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Nov 2019
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B23-Circular Dichroism
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Janaki
Shanmugam
,
Konstantin B.
Borisenko
,
Andrew
Luers
,
Paul
Ewart
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Priyav
Shah
,
Benjamin A. O.
Williams
,
Christopher
Craig
,
Daniel W.
Hewak
,
Rohanah
Hussain
,
Tamas
Javorfi
,
Giuliano
Siligardi
,
Michel
Bosman
,
Angus I.
Kirkland
Diamond Proposal Number(s):
[9375, 15028]
Abstract: Induction, tuning, or amplification of chirality in various classes of materials and probing their chiral response are subjects of growing research. Herein, a large chiral signal that is rapidly imprinted in achiral amorphous Ge2Sb2Te5 (GST) thin films measured using synchrotron circular dichroism spectroscopy is reported. The chirality is induced by illuminating the films with pulsed circularly polarized (chiral) laser light for less than 2 μs in total. The effects of laser fluence and film thickness on the chiral response are described. The correlation of the optical results with structural studies by electron diffraction and model simulations suggests that alignment of reamorphized fragments in the crystallized film along the electric field vector of the light forms the centers that are responsible for the observed chirality. These results suggest opportunities for practical applications of this phenomenon and provide avenues for further studies of chirality induction in materials with impact in a wide range of disciplines.
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Oct 2019
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B23-Circular Dichroism
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Diamond Proposal Number(s):
[8714, 9786, 11563, 18011, 2023, 2074, 5718, 5950, 4980, 12182, 14484, 16778, 19680, 8681]
Abstract: Circular dichroism is the differential absorption of left and right circularly polarized light (CPL) of chiral molecules. Molecules that do not superimpose their mirror images are chiral like L and D amino acids, of which the L enantiomers are the building blocks of proteins and analogously D-deoxyribose for DNA.
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Sep 2019
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B23-Circular Dichroism
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Diamond Proposal Number(s):
[14986]
Abstract: We highlight the power of electronic circular dichroism imaging (CDi), a technique developed at Diamond Light Source B23 beamline for synchrotron radiation circular dichroism (SRCD) to detect local domains of chiral supramolecular order in thin films of chiral oligomers and polymers. The highly brilliant and collimated beamlight of B23 enabled CDi at a spatial resolution of 0.1 mm, unattainable with benchtop electronic circular dichroism (ECD) spectropolarimeters. CDi is bridging the gap between standard ECD spectroscopy and conventional microscopy. Presently, we apply CDi to reveal the local polymorphism of chiral oligothiophene-based molecules. By extensive use of a post-acquisition data-analysis tool called similarity factor, we quantified the polymorphs revealing a manifold of aggregation pathways whose relative weight was function of the sample preparation protocol. This work uncovers the parameters that need to be optimised in order to obtain reproducible and controllable supramolecular structures in thin films, which is of paramount importance for materials with optoelectronic properties. Noteworthy, this analysis is based on the CDi measurement at high spatial resolution of the thin film of organic chiral semiconductor at the ultimate stage of preparation as the active layer of an optoelectronic device.
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Aug 2019
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B23-Circular Dichroism
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Inna M.
Yasinska
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Svetlana S.
Sakhnevych
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Ludmila
Pavlova
,
Anette
Teo Hansen Selnø
,
Ana Maria
Teuscher Abeleira
,
Ouafa
Benlaouer
,
Isabel
Gonçalves Silva
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Marianne
Mosimann
,
Luca
Varani
,
Marco
Bardelli
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Rohanah
Hussain
,
Giuliano
Siligardi
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Dietmar
Cholewa
,
Steffen M.
Berger
,
Bernhard F.
Gibbs
,
Yuri A.
Ushkaryov
,
Elizaveta
Fasler-kan
,
Elena
Klenova
,
Vadim V.
Sumbayev
Diamond Proposal Number(s):
[20755]
Open Access
Abstract: Human cancer cells operate a variety of effective molecular and signaling mechanisms which allow them to escape host immune surveillance and thus progress the disease. We have recently reported that the immune receptor Tim-3 and its natural ligand galectin-9 are involved in the immune escape of human acute myeloid leukemia (AML) cells. These cells use the neuronal receptor latrophilin 1 (LPHN1) and its ligand fibronectin leucine rich transmembrane protein 3 (FLRT3, and possibly other ligands) to trigger the pathway. We hypothesized that the Tim-3-galectin-9 pathway may be involved in the immune escape of cancer cells of different origins. We found that studied breast tumors expressed significantly higher levels of both galectin-9 and Tim-3 compared to healthy breast tissues of the same patients and that these proteins were co-localized. Increased levels of LPHN2 and expressions of LPHN3 as well as FLRT3 were also detected in breast tumor cells. Activation of this pathway facilitated the translocation of galectin-9 onto the tumor cell surface, however no secretion of galectin-9 by tumor cells was observed. Surface-based galectin-9 was able to protect breast carcinoma cells against cytotoxic T cell-induced death. Furthermore, we found that cell lines from brain, colorectal, kidney, blood/mast cell, liver, prostate, lung, and skin cancers expressed detectable amounts of both Tim-3 and galectin-9 proteins. The majority of cell lines expressed one of the LPHN isoforms and FLRT3. We conclude that the Tim-3-galectin-9 pathway is operated by a wide range of human cancer cells and is possibly involved in prevention of anti-tumor immunity.
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Jul 2019
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B23-Circular Dichroism
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Diamond Proposal Number(s):
[13463, 11528, 14298]
Abstract: Trichogin is a natural peptide endowed with antimicrobial and antitumor activity. A member of the peptaibol family, trichogin possesses a C‐terminal aminoalcohol. In the past, we substituted that moiety with a methyl ester for synthetic purposes and realized that this apparently slight modification causes great changes in the peptide bioactivity. Aiming at understanding the reasons behind such observations, we performed a detailed spectroscopic study on a number of trichogin analogs. In the present manuscript, we compare the data obtained from synchrotron radiation circular dichroism, NMR and fluorescence spectroscopy in organic solvents at cryogenic temperatures with those independently acquired by electron paramagnetic resonance spectroscopy at 80K. We reveal unambiguously the presence of a reversible, temperature‐driven screw‐sense interconversion from right‐handed to left‐handed helix that is determined by the C‐terminal capping moiety. Our data demonstrate for the first time the key role of a C‐terminal methyl ester in promoting peptide screw‐sense inversion.
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May 2019
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