Tag Archives: Xiaozhou (Michelle) Zhang

First reversible ‘turn-off’ sensor for Glutathione

6 September 2017:

The first reversible ‘turn-off’ sensor for Glutathione has been reported by CNBP researchers in a paper published in the science journal Biosensors.

The paper is accessible online (open access).

Dr Sabrina Heng notes:

γ-Glutamyl-cysteinyl-glycine (GSH) plays a critical role in maintaining redox homeostasis in biological systems and a decrease in its cellular levels is associated with disease. Many diseases including Parkinson’s, cancer, heart diseases and Alzheimer’s are indicated by a decrease in GSH levels. In this case, a ‘turn on’ sensor would result in reduced fluorescence relative to healthy cells. An important advance would come from the development of a sensor that is measurably turned off by GSH and back on by a lower level of GSH. This would then provide an opportunity to sense reduced GSH levels during the onset of important diseases.

With that in mind we have rationally designed, to the best of our knowledge, the first reversible, reaction-based ‘turn-off’ probe that is suitable for sensing decreasing levels of GSH, a situation known to occur at the onset of various diseases.  We have demonstrated that the sensor can be used to detect changes of intracellular GSH in live HEK 293 cells to provide a potentially regenerable sensor for monitoring lower levels of intracellular GSH as associated with the onset of important diseases.

Journal: Biosensors.

Publication title: A Rationally Designed Reversible ‘Turn-Off’ Sensor for Glutathione.

Authors: Sabrina Heng (pictured), Xiaozhou Zhang, Jinxin Pei and Andrew D. Abell.

Abstract: γ-Glutamyl-cysteinyl-glycine (GSH) plays a critical role in maintaining redox homeostasis in biological systems and a decrease in its cellular levels is associated with diseases. Existing fluorescence-based chemosensors for GSH acts as irreversible reaction-based probes that exhibit a maximum fluorescence (‘turn-on’) once the reaction is complete, regardless of the actual concentration of GSH. A reversible, reaction-based ‘turn-off’ probe (1) is reported here to sense the decreasing levels of GSH, a situation known to occur at the onset of various diseases. The more fluorescent merocyanine (MC) isomer of 1 exists in aqueous solution and this reacts with GSH to induce formation of the ring-closed spiropyran (SP) isomer, with a measurable decrease in absorbance and fluorescence (‘turn-off’). Sensor 1 has good aqueous solubility and shows an excellent selectivity for GSH over other biologically relevant metal ions and aminothiol analytes. The sensor permeates HEK 293 cells and an increase in fluorescence is observed on adding buthionine sulfoximine, an inhibitor of GSH synthesis.

Sensors for calcium ion

15 June 2017:

Researchers from CNBP (lead author Dr Sabrina Heng pictured), have just had a paper published, reporting on three new spiropyran-based reversible sensors for calcium ion.

Journal: Sensors and Actuators B: Chemical.

Publication title: Photoswitchable calcium sensor: ‘On’–‘Off’ sensing in cells or with microstructured optical fibers.

Authors: Sabrina Heng, Adrian M. Mak, Roman Kostecki, Xiaozhou Zhang, Jinxin Peia, Daniel B. Stubing, Heike Ebendorff-Heidepriema, Andrew D. Abell.

Abstract: Calcium is a ubiquitous intracellular signaling ion that plays a critical role in the modulation of fundamental cellular processes. A detailed study of these processes requires selective and reversible sensing of Ca2+ and an ability to quantify and monitor concentration changes in a biological setting. Three new, rationally designed, synthesized and photoswitchable spiropyran-based reversible sensors for Ca2+ are reported. Sensor 1a is highly selective for Ca2+ with an improved profile relative to the other two analogues, 1b and 1c. Formation of the merocyanine–Ca2+ complex is proportional to an increase in Ca2+ released from HEK293 cells on stimulation with ionomycin. The photophysical processes surrounding the binding of Ca2+ to compound 1a were further explored using computational methods based on density functional theory (DFT). The ability of sensor 1a to bind Ca2+ and photoswitch reversibly was also characterized using silica suspended-core microstructured optical fiber (SCF). These SCF experiments (with 100 nM Ca2+) represent a first step toward developing photoswitchable, minimally invasive and highly sensitive Ca2+ sensing platforms for use in a biological setting.

The paper is accessible online.

Inhibition of α-chymotrypsin

Michelle-Zhang_1_sq23 June 2016:

CNBP researchers Xiaozhou (Michelle) Zhang  (pictured left) and Prof Andrew Abell (CNBP Chief Investigator) report on an NMR and X-ray crystallography-based characterisation of the mechanism by which a new class of macrocyclic peptidomimetic aldehyde inhibits α-chymotrypsin.

This provides molecular level insight into the mechanism and functionalities of proteases, which are crucial for many biological systems including neuronal, embryonic and cardiovascular systems.

Journal: Organic & Biomolecular Chemistry

Publication title: A mechanistic study on the inhibition of α-chymotrypsin by a macrocyclic peptidomimetic aldehyde.

Authors: X. Zhang, J. B. Bruning, J. H. George and A. D. Abell

Abstract: Here we describe an NMR and X-ray crystallography-based characterisation of the mechanism by which a new class of macrocyclic peptidomimetic aldehyde inhibits α-chymotrypsin. In particular, a 13C-labelled analogue of the inhibitor was prepared and used in NMR experiments to confirm formation of a hemiacetal intermediate on binding with α-chymotrypsin. Analysis of an X-ray crystallographic structure in complex with α-chymotrypsin reveals that the backbone adopts a stable β-strand conformation as per its design. Binding is further stabilised by interaction with the oxyanion hole near the S1 subsite and multiple hydrogen bonds.

The paper is accessible online.

IPAS best papers competition

cnbplogosquare129 January 2016:

CNBP researchers featured prominently in the recent ‘Institute for Photonics and Advanced Sensing (IPAS) Best Papers’ competition.

The awards, presented in January 2016,  aim to showcase the quality and impact of the research being conducted by IPAS members.

Winners for the best ECR led Paper were Abel Santos, Agnieszka Zuber and CNBP Research Fellow Xiaozhou (Michelle) Zhang.

The best PhD Student Led Paper Awards went to CNBP student Malcolm Purdey, Parul Mittal and Tess Reynolds.

The Best Transdisciplinary Paper with a Strong Medical/Animal Science Element went to CNBP senior researcher Melanie McDowall.

Full details on the awards, all of the winners and their papers can be found at the IPAS web site.