Yichong Fan

Bio: Yichong Fan is an academic researcher from Oak Ridge National Laboratory. The author has contributed to research in topics: Green fluorescent protein & Endoplasmic reticulum. The author has an hindex of 4, co-authored 6 publications receiving 137 citations. Previous affiliations of Yichong Fan include University of Virginia & University of California, Riverside.

A Sensitive Near-Infrared Fluorescent Sensor for Mitochondrial Hydrogen Sulfide

Abstract: Hydrogen sulfide (H2S) is an important gasotransmitter. Although a large number of fluorescent probes for cellular H2S have been reported, only a few can detect H2S in mitochondria, a cellular organelle connecting H2S with mitochondrial function and metabolic pathways. We hereby describe a novel near-infrared fluorescent probe, nimazide, by introducing sulfonyl azide to the core structure of a QSY-21 dark quencher. Nimazide responded quickly to H2S, resulting in robust fluorescence turn-off changes. This conversion displayed high specificity and fast kinetics. More impressively, we observed a robust fluorescence decrease in live cells loaded with mitochondrial nimazide in response to extracellular addition of nanomolar H2S, and successfully imaged biologically generated mitochondrial H2S in live mammalian cells. Nimazide is one of the most sensitive fluorescent probes for mitochondrial H2S.

Monitoring redox dynamics in living cells with a redox-sensitive red fluorescent protein.

Abstract: Redox signaling and homeostasis are important for all forms of life on Earth. There has been great interest in monitoring redox dynamics in living cells and organisms as a mean to better understand redox biology in physiological and pathological conditions. Herein we report our recent results on the development of a genetically encoded redox-sensitive red fluorescent protein (rxRFP). We first identified a circularly permuted RFP (cpRFP) scaffold, which maintained its autocatalytic fluorescence, from a red fluorescent Ca(2+) sensor, R-GECO1. We then introduced cysteine residue pairs to the N- and C- termini of the cpRFP scaffold, and subsequently optimized the length and composition of the sequences adjacent to the cysteine residues. From these libraries, we identified rxRFP, showing up to a 4-fold fluorescence increase in the oxidized state compared to the reduced state at pH 7.4. We thoroughly characterized rxRFP in vitro, and expressed it in living mammalian cells to monitor redox dynamics. With its excitation peak at 576 nm and emission peak at 600 nm, rxRFP is one of the first genetically encoded red fluorescent probes that can sense general redox states.

Monitoring thioredoxin redox with a genetically encoded red fluorescent biosensor

Abstract: Thioredoxin (Trx) is one of the two major thiol antioxidants, playing essential roles in redox homeostasis and signaling. Despite its importance, there is a lack of methods for monitoring Trx redox dynamics in live cells, hindering a better understanding of physiological and pathological roles of the Trx redox system. In this work, we developed the first genetically encoded fluorescent biosensor for Trx redox by engineering a redox relay between the active-site cysteines of human Trx1 and rxRFP1, a redox-sensitive red fluorescent protein. We used the resultant biosensor-TrxRFP1-to selectively monitor perturbations of Trx redox in various mammalian cell lines. We subcellularly localized TrxRFP1 to image compartmentalized Trx redox changes. We further combined TrxRFP1 with a green fluorescent Grx1-roGFP2 biosensor to simultaneously monitor Trx and glutathione redox dynamics in live cells in response to chemical and physiologically relevant stimuli.

Development of redox-sensitive red fluorescent proteins for imaging redox dynamics in cellular compartments.

Abstract: We recently reported a redox-sensitive red fluorescent protein, rxRFP1, which is one of the first genetically encoded red-fluorescent probes for general redox states in living cells. As individual cellular compartments have different basal redox potentials, we hereby describe a group of rxRFP1 mutants, showing different midpoint redox potentials for detection of redox dynamics in various subcellular domains, such as mitochondria, the cell nucleus, and endoplasmic reticulum (ER). When these redox probes were expressed and subcellularly localized in human embryonic kidney (HEK) 293 T cells, they responded to membrane-permeable oxidants and reductants. In addition, a mitochondrially localized rxRFP1 mutant, Mito-rxRFP1.1, was used to detect mitochondrial oxidative stress induced by doxorubicin-a widely used cancer chemotherapy drug. Our work has expanded the fluorescent protein toolkit with new research tools for studying compartmentalized redox dynamics and oxidative stress under various pathophysiological conditions.

Genetically Encoded Fluorescent Biosensors Illuminate the Spatiotemporal Regulation of Signaling Networks.

Abstract: Cellular signaling networks are the foundation which determines the fate and function of cells as they respond to various cues and stimuli. The discovery of fluorescent proteins over 25 years ago enabled the development of a diverse array of genetically encodable fluorescent biosensors that are capable of measuring the spatiotemporal dynamics of signal transduction pathways in live cells. In an effort to encapsulate the breadth over which fluorescent biosensors have expanded, we endeavored to assemble a comprehensive list of published engineered biosensors, and we discuss many of the molecular designs utilized in their development. Then, we review how the high temporal and spatial resolution afforded by fluorescent biosensors has aided our understanding of the spatiotemporal regulation of signaling networks at the cellular and subcellular level. Finally, we highlight some emerging areas of research in both biosensor design and applications that are on the forefront of biosensor development.

Dissecting Redox Biology Using Fluorescent Protein Sensors

Abstract: Significance: Fluorescent protein sensors have revitalized the field of redox biology by revolutionizing the study of redox processes in living cells and organisms. Recent Advances: Within one decade, a set of fundamental new insights has been gained, driven by the rapid technical development of in vivo redox sensing. Redox-sensitive yellow and green fluorescent protein variants (rxYFP and roGFPs) have been the central players. Critical Issues: Although widely used as an established standard tool, important questions remain surrounding their meaningful use in vivo. We review the growing range of thiol redox sensor variants and their application in different cells, tissues, and organisms. We highlight five key findings where in vivo sensing has been instrumental in changing our understanding of redox biology, critically assess the interpretation of in vivo redox data, and discuss technical and biological limitations of current redox sensors and sensing approaches. Future Directions: We explore how...

Optical Sensing and Imaging of pH Values: Spectroscopies, Materials, and Applications

Abstract: This is the first comprehensive review on methods and materials for use in optical sensing of pH values and on applications of such sensors. The Review starts with an introduction that contains subsections on the definition of the pH value, a brief look back on optical methods for sensing of pH, on the effects of ionic strength on pH values and pKa values, on the selectivity, sensitivity, precision, dynamic ranges, and temperature dependence of such sensors. Commonly used optical sensing schemes are covered in a next main chapter, with subsections on methods based on absorptiometry, reflectometry, luminescence, refractive index, surface plasmon resonance, photonic crystals, turbidity, mechanical displacement, interferometry, and solvatochromism. This is followed by sections on absorptiometric and luminescent molecular probes for use pH in sensors. Further large sections cover polymeric hosts and supports, and methods for immobilization of indicator dyes. Further and more specific sections summarize the state of the art in materials with dual functionality (indicator and host), nanomaterials, sensors based on upconversion and 2-photon absorption, multiparameter sensors, imaging, and sensors for extreme pH values. A chapter on the many sensing formats has subsections on planar, fiber optic, evanescent wave, refractive index, surface plasmon resonance and holography based sensor designs, and on distributed sensing. Another section summarizes selected applications in areas, such as medicine, biology, oceanography, bioprocess monitoring, corrosion studies, on the use of pH sensors as transducers in biosensors and chemical sensors, and their integration into flow-injection analyzers, microfluidic devices, and lab-on-a-chip systems. An extra section is devoted to current challenges, with subsections on challenges of general nature and those of specific nature. A concluding section gives an outlook on potential future trends and perspectives.

Methods for the detection of reactive oxygen species

Abstract: There are many pieces of evidence suggesting the mediating role of reactive oxygen species (ROS) in cell life, stress and death, and it is known that ROS at different concentrations would play distinctly different roles therein, thus eventually leading to the different fates of cells. Therefore it is highly necessary to carry out a reliable measurement of the concentration or relative level of ROS. Many means are available for ROS detection, such as the classical and commonly used spectrophotometry methods, use of fluorescence and chemiluminescence probes, and electron spin resonance (ESR/EPR), which provide direct identification of different types of oxygen radicals. In addition, fluorescent protein-based redox indicators designed for monitoring redox status changes would also be introduced in the text. Considering the fact that each type of method mentioned above has drawbacks during application, the present review tries to make a comparison and summary of their advantages and disadvantages systemically, and as a conclusion, the rational use of more than one method is recommended for better testing of the free radicals in cells.