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1358 Publications

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    12/14/20 | Label-free imaging of fibroblast membrane interfaces and protein signatures with vibrational infrared photothermal and phase signals.
    Samolis PD, Langley D, O'Reilly BM, Oo Z, Hilzenrat G, Erramilli S, Sgro AE, McArthur S, Sander MY
    Biomed Opt Express. 12/2020;12(1):303-319. doi: 10.1364/BOE.411888

    Label-free vibrational imaging of biological samples has attracted significant interest due to its integration of structural and chemical information. Vibrational infrared photothermal amplitude and phase signal (VIPPS) imaging provide label-free chemical identification by targeting the characteristic resonances of biological compounds that are present in the mid-infrared fingerprint region (3 µm - 12 µm). High contrast imaging of subcellular features and chemical identification of protein secondary structures in unlabeled and labeled fibroblast cells embedded in a collagen-rich extracellular matrix is demonstrated by combining contrast from absorption signatures (amplitude signals) with sensitive detection of different heat properties (lock-in phase signals). We present that the detectability of nano-sized cell membranes is enhanced to well below the optical diffraction limit since the membranes are found to act as thermal barriers. VIPPS offers a novel combination of chemical imaging and thermal diffusion characterization that paves the way towards label-free imaging of cell models and tissues as well as the study of intracellular heat dynamics.

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    08/01/20 | Sensing cellular biochemistry with fluorescent chemical–genetic hybrids
    Gautier A, Tebo AG
    Current Opinion in Chemical Biology. 08/2020;57:58–64. doi: 10.1016/j.cbpa.2020.04.005

    Fluorescent biosensors are powerful tools for the detection of biochemical events inside cells with high spatiotemporal resolution. Biosensors based on fluorescent proteins often suffer from issues with photostability and brightness. On the other hand, hybrid, chemical–genetic systems present unique opportunities to combine the strengths of synthetic, organic chemistry with biological macromolecules to generate exquisitely tailored semisynthetic sensors.

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    09/25/20 | Integrated structure-function dataset reveals key mechanisms underlying photochromic fluorescent proteins
    Zitter ED, Hugelier S, Duwé S, Vandenberg W, Tebo AG, Meervelt LV, Dedecker P
    bioRxiv. 09/2020:2020.09.25.313528. doi: 10.1101/2020.09.25.313528

    Photochromic fluorescent proteins have become versatile tools in the life sciences, though our understanding of their structure-function relation is limited. Starting from a single scaffold, we have developed a range of 27 photochromic fluorescent proteins that cover a broad range of spectroscopic properties, yet differ only in one or two mutations. We also determined 43 different crystal structures of these mutants. Correlation and principal component analysis of the spectroscopic and structural properties confirmed the complex relationship between structure and spectroscopy, suggesting that the observed variability does not arise from a limited number of mechanisms, but also allowed us to identify consistent trends and to relate these to the spatial organization around the chromophore. We find that particular changes in spectroscopic properties can come about through multiple different underlying mechanisms, of which the polarity of the chromophore environment and hydrogen bonding of the chromophore are key modulators. Furthermore, some spectroscopic parameters, such as the photochromism, appear to be largely determined by a single or a few structural properties, while other parameters, such as the absorption maximum, do not allow a clear identification of a single cause. We also highlight the role of water molecules close to the chromophore in influencing photochromism. We anticipate that our dataset can open opportunities for the development and evaluation of new and existing protein engineering methods.

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    08/17/20 | An enzymatic toolkit for selective proteolysis, detection, and visualization of mucin-domain glycoproteins
    Shon DJ, Malaker SA, Pedram K, Yang E, Krishnan V, Dorigo O, Bertozzi CR
    Proceedings of the National Academy of Sciences. Jan-09-2020;117(35):21299 - 21307. doi: 10.1073/pnas.2012196117

    Densely O-glycosylated mucin domains are found in a broad range of cell surface and secreted proteins, where they play key physiological roles. In addition, alterations in mucin expression and glycosylation are common in a variety of human diseases, such as cancer, cystic fibrosis, and inflammatory bowel diseases. These correlations have been challenging to uncover and establish because tools that specifically probe mucin domains are lacking. Here, we present a panel of bacterial proteases that cleave mucin domains via distinct peptide- and glycan-based motifs, generating a diverse enzymatic toolkit for mucin-selective proteolysis. By mutating catalytic residues of two such enzymes, we engineered mucin-selective binding agents with retained glycoform preferences. StcEE447D is a pan-mucin stain derived from enterohemorrhagic Escherichia coli that is tolerant to a wide range of glycoforms. BT4244E575A derived from Bacteroides thetaiotaomicron is selective for truncated, asialylated core 1 structures commonly associated with malignant and premalignant tissues. We demonstrated that these catalytically inactive point mutants enable robust detection and visualization of mucin-domain glycoproteins by flow cytometry, Western blot, and immunohistochemistry. Application of our enzymatic toolkit to ascites fluid and tissue slices from patients with ovarian cancer facilitated characterization of patients based on differences in mucin cleavage and expression patterns.


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    04/05/20 | Orthogonal fluorescent chemogenetic reporters for multicolor imaging
    Tebo AG, Moeyaert B, Thauvin M, Carlon-Andres I, Böken D, Volovitch M, Padilla-Parra S, Dedecker P, Vriz S, Gautier A
    Nature Chemical Biology. 04/2020:1–9. doi: 10.1038/s41589-020-0611-0

    Spectrally separated fluorophores allow the observation of multiple targets simultaneously inside living cells, leading to a deeper understanding of the molecular interplay that regulates cell function and fate. Chemogenetic systems combining a tag and a synthetic fluorophore provide certain advantages over fluorescent proteins since there is no requirement for chromophore maturation. Here, we present the engineering of a set of spectrally orthogonal fluorogen-activating tags based on the fluorescence-activating and absorption shifting tag (FAST) that are compatible with two-color, live-cell imaging. The resulting tags, greenFAST and redFAST, demonstrate orthogonality not only in their fluorogen recognition capabilities, but also in their one- and two-photon absorption profiles. This pair of orthogonal tags allowed the creation of a two-color cell cycle sensor capable of detecting very short, early cell cycles in zebrafish development and the development of split complementation systems capable of detecting multiple protein–protein interactions by live-cell fluorescence microscopy. The fluorescent chemogenetic reporters greenFAST and redFAST were engineered by protein engineering. They display orthogonal fluorogen recognition and spectral properties allowing efficient multicolor imaging of proteins in live cells and organisms.

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    07/29/20 | Lysosome-targeting chimaeras for degradation of extracellular proteins
    Banik SM, Pedram K, Wisnovsky S, Ahn G, Riley NM, Bertozzi CR
    Nature. Jan-08-2021;584(7820):291 - 297. doi: 10.1038/s41586-020-2545-9

    The majority of therapies that target individual proteins rely on specific activity-modulating interactions with the target protein—for example, enzyme inhibition or ligand blocking. However, several major classes of therapeutically relevant proteins have unknown or inaccessible activity profiles and so cannot be targeted by such strategies. Protein-degradation platforms such as proteolysis-targeting chimaeras (PROTACs)1,2 and others (for example, dTAGs3, Trim-Away4, chaperone-mediated autophagy targeting5 and SNIPERs6) have been developed for proteins that are typically difficult to target; however, these methods involve the manipulation of intracellular protein degradation machinery and are therefore fundamentally limited to proteins that contain cytosolic domains to which ligands can bind and recruit the requisite cellular components. Extracellular and membrane-associated proteins—the products of 40% of all protein-encoding genes7—are key agents in cancer, ageing-related diseases and autoimmune disorders8, and so a general strategy to selectively degrade these proteins has the potential to improve human health. Here we establish the targeted degradation of extracellular and membrane-associated proteins using conjugates that bind both a cell-surface lysosome-shuttling receptor and the extracellular domain of a target protein. These initial lysosome-targeting chimaeras, which we term LYTACs, consist of a small molecule or antibody fused to chemically synthesized glycopeptide ligands that are agonists of the cation-independent mannose-6-phosphate receptor (CI-M6PR). We use LYTACs to develop a CRISPR interference screen that reveals the biochemical pathway for CI-M6PR-mediated cargo internalization in cell lines, and uncover the exocyst complex as a previously unidentified—but essential—component of this pathway. We demonstrate the scope of this platform through the degradation of therapeutically relevant proteins, including apolipoprotein E4, epidermal growth factor receptor, CD71 and programmed death-ligand 1. Our results establish a modular strategy for directing secreted and membrane proteins for lysosomal degradation, with broad implications for biochemical research and for therapeutics.


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    07/09/20 | Nurturing Undergraduate Researchers in Biomedical Sciences.
    Li J, Luo L
    Cell. 07/2020;182(1):1-4. doi: 10.1016/j.cell.2020.05.008

    Undergraduate researchers are the next-generation scientists. Here, we call for more attention from our community to the proper training of undergraduates in biomedical research laboratories. By dissecting common pitfalls, we suggest how to better mentor undergraduates and prepare them for flourishing careers.

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    06/22/20 | A far‐red fluorescent chemogenetic reporter for in vivo molecular imaging
    Li C, Tebo AG, Thauvin M, Plamont M, Volovitch M, Morin X, Vriz S, Gautier A
    Angewandte Chemie International Edition. 06/2020:. doi: 10.1002/anie.202006576

    Far‐red emitting fluorescent labels are highly desirable for spectral multiplexing and deep tissue imaging. Here, we describe the generation of frFAST (far‐red Fluorescence Activating and absorption Shifting Tag), a 14‐kDa monomeric protein that forms a bright far‐red fluorescent assembly with (4‐hydroxy‐3‐methoxy‐phenyl)allylidene rhodanine (HPAR‐3OM). As HPAR‐3OM is essentially non‐ fluorescent in solution and in cells, frFAST can be imaged with high contrast in presence of free HPAR‐3OM, which allowed the rapid and efficient imaging of frFAST fusions in live cells, zebrafish embryo/larvae and chicken embryo. Beyond enabling genetic encoding of far‐red fluorescence, frFAST allowed the design of a far‐ red chemogenetic reporter of protein‐protein interactions, demonstrating its great potential for the design of innovative far‐red emitting biosensors.

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    05/12/20 | Intracellular signaling dynamics and their role in coordinating tissue repair.
    Ghilardi SJ, O'Reilly BM, Sgro AE
    Wiley Interdiscip Rev Syst Biol Med. 05/2020;12(3):e1479. doi: 10.1002/wsbm.1479

    Tissue repair is a complex process that requires effective communication and coordination between cells across multiple tissues and organ systems. Two of the initial intracellular signals that encode injury signals and initiate tissue repair responses are calcium and extracellular signal-regulated kinase (ERK). However, calcium and ERK signaling control a variety of cellular behaviors important for injury repair including cellular motility, contractility, and proliferation, as well as the activity of several different transcription factors, making it challenging to relate specific injury signals to their respective repair programs. This knowledge gap ultimately hinders the development of new wound healing therapies that could take advantage of native cellular signaling programs to more effectively repair tissue damage. The objective of this review is to highlight the roles of calcium and ERK signaling dynamics as mechanisms that link specific injury signals to specific cellular repair programs during epithelial and stromal injury repair. We detail how the signaling networks controlling calcium and ERK can now also be dissected using classical signal processing techniques with the advent of new biosensors and optogenetic signal controllers. Finally, we advocate the importance of recognizing calcium and ERK dynamics as key links between injury detection and injury repair programs that both organize and execute a coordinated tissue repair response between cells across different tissues and organs. This article is categorized under: Models of Systems Properties and Processes > Mechanistic Models Biological Mechanisms > Cell Signaling Laboratory Methods and Technologies > Imaging Models of Systems Properties and Processes > Organ, Tissue, and Physiological Models.

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    04/06/20 | Single-Cell Transcriptomes Reveal Diverse Regulatory Strategies for Olfactory Receptor Expression and Axon Targeting.
    Li H, Li T, Horns F, Li J, Xie Q, Xu C, Wu B, Kebschull JM, McLaughlin CN, Kolluru SS, Jones RC, Vacek D, Xie A, Luginbuhl DJ, Quake SR, Luo L
    Curr Biol. 04/2020;30(7):1189-1198.e5. doi: 10.1016/j.cub.2020.01.049

    The regulatory mechanisms by which neurons coordinate their physiology and connectivity are not well understood. The Drosophila olfactory receptor neurons (ORNs) provide an excellent system to investigate this question. Each ORN type expresses a unique olfactory receptor, or a combination thereof, and sends their axons to a stereotyped glomerulus. Using single-cell RNA sequencing, we identified 33 transcriptomic clusters for ORNs and mapped 20 to their glomerular types, demonstrating that transcriptomic clusters correspond well with anatomically and physiologically defined ORN types. Each ORN type expresses hundreds of transcription factors. Transcriptome-instructed genetic analyses revealed that (1) one broadly expressed transcription factor (Acj6) only regulates olfactory receptor expression in one ORN type and only wiring specificity in another type, (2) one type-restricted transcription factor (Forkhead) only regulates receptor expression, and (3) another type-restricted transcription factor (Unplugged) regulates both events. Thus, ORNs utilize diverse strategies and complex regulatory networks to coordinate their physiology and connectivity.

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