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CD22 is a negative regulator of B-cell receptor signaling, an activity mediated by recruitment of SH2 domain–containing phosphatase 1 through a phosphorylated immunoreceptor tyrosine inhibitory motif in its cytoplasmic domain. As in other members of the sialic acid–binding immunoglobulin-like lectin, or siglec, family, the extracellular N-terminal immunoglobulin domain of CD22 binds to glycan ligands containing sialic acid, which are highly expressed on B-cell glycoproteins. B-cell glycoproteins bind to CD22 in cis and 'mask' the ligand-binding domain, modulating its activity as a regulator of B-cell signaling. To assess cell-surface cis ligand interactions, we developed a new method for in situ photoaffinity cross-linking of glycan ligands to CD22. Notably, CD45, surfaceIgM (sIgM) and other glycoproteins that bind to CD22 in vitro do not appear to be important cis ligands of CD22 in situ. Instead, CD22 seems to recognize glycans of neighboring CD22 molecules as cis ligands, forming homomultimeric complexes. [ABSTRACT FROM AUTHOR]

The hydration of CO2 catalyzed by human carbonic anhydrase II (HCA II) is accompanied by proton transfer from the zinc-bound water of the enzyme to solution. We have replaced the proton shuttling residue His 64 with Ala and placed cysteine residues within the active-site cavity by mutating sites Trp 5, Asn 62, Ile 91, and Phe 131. These mutants were modified at the single inserted cysteine with imidazole analogs to introduce new potential shuttle groups. Catalysis by these modified mutants was determined by stopped-flow and 18O-exchange methods. Specificity in proton transfer was demonstrated; only modifications of the Cys 131-containing mutant showed enhancement in the proton transfer step of catalysis compared with unmodified Cys 131-containing mutant. Modifications at other sites resulted in up to 3-fold enhancement in rates of CO2 hydration, with apparent second-order rate constants near 350 μM−1 s−1. These are among the largest values of kcat/Km observed for a carbonic anhydrase. [Copyright &y& Elsevier]

Two novel carboxyl-containing arginase substrates, 4-guanidino-3-nitrobenzoic acid and 4-guanidino-2-nitrophenylacetic acid, have been synthesized and found to give enhanced catalysis and dramatically lower Km values relative to 1-nitro-3-guanidinobenzene, a substrate designed for use in a chromophoric arginase assay. To more efficiently mimic the natural substrate, a series of sulfur analogs of l-arginine were synthesized and kinetically characterized. The parent compound, l-thioarginine, with the bridging guanidinium nitrogen of l-arginine replaced with sulfur, functions as efficiently as the natural substrate. The desamino analog shows extremely low turnover, while the kcat of the descarboxy analog is only 75-fold lower than that of arginine. These results suggest that the bridging nitrogen of l-arginine is not important for either substrate binding or catalysis, while the α-carboxyl group facilitates substrate binding, and the α-amino group is necessary for efficient catalysis. Isothiourea homologs previously reported to be nitric oxide synthase inhibitors have been found to undergo a rapid non-enzymatic rearrangement to a species that is probably the true inhibitor. [Copyright &y& Elsevier]

Imaging of mitophagy is of significance as aberrant mitophagy is engaged in multiple diseases. Mitophagy has been imaged with synthetic or biotic pH sensors by reporting pH acidification en route delivery into lysosomes. To circumvent uncertainty of acidity-dependent signals, we herein report an enzyme-activatable probe covalently attached on mitochondrial inner membrane (ECAM) for signal-persist mitophagy imaging. ECAM is operated via ΔΨm-driven accumulation of Mito-proGreen in mitochondria and covalent linking of the trapped probe with azidophospholipids metabolically incorporated into the mitochondrial inner membrane. Upon mitophagy, ECAM is delivered into lysosomes and hydrolyzed by LNPEP/leucyl aminopeptidase, yielding turn-on green fluorescence that is immune to lysosomal acidity changes and stably retained in fixed cells. With ECAM, phorbol-12-myristate-13-acetate (PMA) was identified as a highly potent inducer of mitophagy. Overcoming signal susceptibility of pH probes and liability of ΔΨm probes to dissipation from stressed mitochondria, ECAM offers an attractive tool to study mitophagy and mitophagy-inducing therapeutic agents.Abbreviations: Baf-A1, bafilomycin A1; CCCP, carbonyl cyanide m-chlorophenylhydrazone; DBCO, dibenzocyclooctyne; ECAM, enzyme-activated probe covalently attached on mitochondrial inner membrane; GFP, green fluorescent protein; LAMP2, lysosomal associated membrane protein 2; LNPEP/LAP, leucyl and cystinyl aminopeptidase; PMA, phorbol-12-myristate-13-acetate; ΔΨm, mitochondrial transmembrane potential; RFP, red fluorescent protein; TPP, triphenylphosphonium. [ABSTRACT FROM AUTHOR]

A visual and fluorogenic detection method for a nerve agent simulant was developed based on a Lossen rearrangement of rhodamine–hydroxamate, in the presence of diethyl chlorophosphate, under alkaline conditions. [ABSTRACT FROM AUTHOR]

The article offers information on a study about the utilization of sialoside analogue arrays in the identification of high affinity siglec ligands. The study demonstrates how sialoside analogue arrays allow for the synthesis of sialoside analogues for the screening of high affinity ligands of siglecs.

TCCSia is preferentially taken up by the tumors and then metabolically installed on cell surface to give a TCCSiaα2,3-Gal epitope that recruits macrophages to trigger antitumor immunity. [Display omitted] Synthetic probes that could direct immune cells against tumors are potential immunotherapeutics. We herein report in vivo tumor suppression via an intravenously injected abiotic sialic acid (TCCSia) that could be metabolically incorporated into tumor cell surface to yield of a high affinity ligand (TCCSiaα2,3-Gal) of Siglec-1 specifically expressed on macrophages. We observed marked suppression of pulmonary metastasis and subcutaneous tumor growth of B16F10 melanoma cells in mice with TCCSia, suggesting the utility of abiotic sialic acid to modulate tumor immunity via recruiting Siglec+ immune cells. [ABSTRACT FROM AUTHOR]

A chromogenic and fluorogenic detection of a nerve agent simulant was developed based on diethyl chlorophosphate triggered tandem phosphorylation and intramolecular cyclization of N-(rhodamine B)-deoxylactam-2-aminoethanol. [ABSTRACT FROM AUTHOR]

Stressed organelles are often challenging to image with canonical organelle probes owing to their propensity to dissipate from stressed organelles. We herein report the imaging of stressed lysosomes with color-switchable glyco-probes that contain an entity of mannose-6-carboxylate or sialic acid for targeting to and long-term retention in stressed lysosomes, and a diad of fluorescein/rhodamine-X-lactam exhibiting dramatic red-to-green fluorescence shift upon pH elevation. Relative to acidotropic dyes prone to dissipate from pH-elevated lysosomes, both glyco-probes are stably trapped in lysosomes without resorting to lysosomal acidity. Importantly, these probes are red emissive in acidic lysosomes (pH 4.5–5.8), but switched to green fluorescence in lysosomes of pH 6.0–7.4, allowing dual color discrimination of lysosomal pH alterations in cell starvation. These results support the use of sugar-armed sensors to investigate stressed lysosomes in biology and disease. [ABSTRACT FROM AUTHOR]

Dying cell clearance is critical for myriad biological processes such as tissue homeostasis. We herein report an enzyme-activated fluorescence cell labeling approach and its use for multicolor imaging of dying cell clearance. Diacetylated 4-hydroxymandelic acid (DHA)-conjugated dyes give rise to reactive quinone methides upon deacetylation in live cells, which in turn covalently labels cellular proteins. With partner cells tagged with distinct fluorescence, apoptotic cell clearance by Raw 264.7 macrophages and epithelial HeLa cells was captured by confocal microscopy, showing the potential of DHA-based cell labeling for investigating cell–cell interactions. [ABSTRACT FROM AUTHOR]

[Display omitted] Imaging or killing of a specific pathogen is of significance for precise therapy. Staphylococcus aureus (S. aureus) is an infectious gram-positive bacteria relying on Sortase A (SrtA) to anchor cell surface protein on peptidoglycan. We herein report signal-on labeling of S. aureus with self-quenched optical probes featuring vancomycin-conjugated SrtA substrate that is flanked by a dabcyl moiety paired with either fluorescein or eosine photosensizer (PS). SrtA-mediated cleavage of the substrate motif releases the dabcyl quencher, leading to covalent labeling of peptidoglycan with fluorescein or PS of restored photophysical property. The dual biomarked-enabled peptidoglycan labeling enables signal-on imaging and effective photodynamic destruction of S. aureus , suggesting a protheranostic approch activatable to SrtA-positive bacteria engaged in myriad diseases. [ABSTRACT FROM AUTHOR]

We report senescence imaging with a fluorescence-quenched self-immolative sialoside probe (Sia-RQ) which gives a reactive quinone methide to allow in situ fluorescence labeling of sialidases upon desialylation. Dramatic upregulation of lysosome-associated sialidase was uncovered in cell senescence with Sia-RQ, suggesting the use of sialidase as a new biomarker for senescence. [ABSTRACT FROM AUTHOR]

Abstract: Selective and continuous tracking of dynamic organelles is crucial for modern biology. We herein report a ship‐in‐a‐bottle strategy for tagging lysosomes by a strain‐promoted azide–alkyne cycloaddition to couple a pH sensor (RC) with mannose‐6‐carboxylate (M6C) actively transported into lysosomes through cell sorting. In contrast to classical acidotropic sensors, which are prone to dissipate from lysosomes, M6C‐RC formed in situ is stably trapped in lysosomes without resort to lysosomal acidity and exhibits “always‐on” blue fluorescence to pinpoint lysosomes and red‐to‐blue fluorescence ratios indicative of the lysosomal pH value. These advantages enable tracking of stressed lysosomes, and necrosis to be differentiated from apoptosis on the basis of lysosomal pH changes. The cell‐sorting‐mediated bioorthogonal tagging strategy offers a new route to track stressed organelles with disrupted physiological organelle–probe affinity. [ABSTRACT FROM AUTHOR]

Abstract: Selective and continuous tracking of dynamic organelles is crucial for modern biology. We herein report a ship‐in‐a‐bottle strategy for tagging lysosomes by a strain‐promoted azide–alkyne cycloaddition to couple a pH sensor (RC) with mannose‐6‐carboxylate (M6C) actively transported into lysosomes through cell sorting. In contrast to classical acidotropic sensors, which are prone to dissipate from lysosomes, M6C‐RC formed in situ is stably trapped in lysosomes without resort to lysosomal acidity and exhibits “always‐on” blue fluorescence to pinpoint lysosomes and red‐to‐blue fluorescence ratios indicative of the lysosomal pH value. These advantages enable tracking of stressed lysosomes, and necrosis to be differentiated from apoptosis on the basis of lysosomal pH changes. The cell‐sorting‐mediated bioorthogonal tagging strategy offers a new route to track stressed organelles with disrupted physiological organelle–probe affinity. [ABSTRACT FROM AUTHOR]

Approaches to increase tumor immunogenicity are of therapeutic potentials. We herein reported the use of liposomes for covalent incorporation of neoantigen on tumor surfaces with DNP-conjugated sialic acid ( DNP Sia). Relative to free DNP Sia, sugar-encapsulated biotinylated liposomes ( DNP Sia@LP@biotin) enables effective cell surface expression of DNP Sia on biotin receptor (BR)-expressing cells over BR-free cells in vitro, and on tumor cell surfaces with high tumor-to-normal tissue contrast in a mice model. These findings suggest the potentials of targetable liposomes for modulating tumor surface immunity via metabolic oligosaccharide engineering. [ABSTRACT FROM AUTHOR]

Rhodamine–silica nanocomposite bridged by a cleavable linker was used for highly sensitive nitrite detection via analyte triggered release of rhodamine from silica particles. Centrifugal removal of pristine nanoconjugate from the assay medium effectively decreased background signals in the supernatant whereas rhodamine unleashed from silica platform is retained in the supernatant, enabling facile detection of nitrite with an assay limit of 50 nM which is 400 folds lower than legislated maximum contaminant levels of nitrite in drinking water. Assays based on small molecular chemosensors are often compromised by their intrinsic fluorescence signals and low aqueous compatibility. The performance of water compatible rhodamine–silica nanocomposite suggests broad analytical potentials of centrifugal nanoparticulate systems with dyes conjugated via appropriate cleavable linkers. [ABSTRACT FROM AUTHOR]

Abstract: Flow cytometric detection of mitochondrial H2S was achieved with propargylic esters of rhodamine B which selectively react with H2S via cationic rhodamine-moiety directed thiolysis of the propargylic esters to give nonfluorescent rhodamine thio-spirolactone. [Copyright &y& Elsevier]

Abstract: Intracellular acidic vesicles, constituted mostly by lysosomes, mediated a variety of biological events ranging from endocytosis, apoptosis, to cancer metastasis, etc. A chimeric molecular pH-meter (Lyso-DR), comprised of a dansyl fluorophore and proton activatable rhodamine-lactam, was prepared for ratiometric reporting of intralysosomal acidity. Exclusively confined in lysosomes, Lyso-DR exhibited pH dependent dual fluorescence emission bands which enable resolution of individual lysosomes in terms of acidity and quantitation of the overall intracellular lysosomal acidity, e.g. the lysosomal pH of HeLa cells is around pH 5.0 whereas that of L929 cells is around pH 6.2. Lyso-DR effectively differentiated the lysosomal pH changes of cells undergoing apoptosis vs necrosis, suggesting its utility in investigations on lysosome involved biomedical processes. [Copyright &y& Elsevier]

Abstract: Two nonfluorescent and colorless chemodosimeters featuring benzothiazoline moiety were developed for chromo-fluorogenic detection of HOCl. [Copyright &y& Elsevier]

Abstract: N-(rhodamine B)-deoxylactam-5-amino-1-pentanol (dRB-APOH) was designed and prepared as the chromo-fluorogenic sensor for detection of a nerve agent simulant via analyte triggered tandem phosphorylation and opening of the intramolecular deoxylactam. The successful detection of diethyl chlorophosphate suggests the utility of rhodamine-deoxylactams as the chromo-fluorogenic signal reporting platform for design of sensors targeting reactive chemical species via various chemistries. [Copyright &y& Elsevier]

Sialoadhesin (Sn, Siglec-1, CD169) is a member of the sialic acid binding Ig-like lectin (siglec) family expressed on macrophages. Its macrophage specific expression makes it an attractive target for delivering antigens to tissue macrophages via Sn-mediated endocytosis. Here we describe a novel approach for delivering antigens to macrophages using liposomal nanoparticles displaying high affinity glycan ligands of Sn. The Sn-targeted liposomes selectively bind to and are internalized by Sn-expressing cells, and accumulate intracellularly over time. Our results show that ligand decorated liposomes are specific for Sn, since they are taken up by bone marrow derived macrophages that are derived from wild type but not Sn-/-mice. Importantly, the Sn-targeted liposomes dramatically enhance the delivery of antigens to macrophages for presentation to and proliferation of antigen-specific T cells. Together, these data provide insights into the potential of cell-specific targeting and delivery of antigens to intracellular organelles of macrophages using Sn-ligand decorated liposomal nanoparticles. [ABSTRACT FROM AUTHOR]

Abstract: Topical microbicides offer women the opportunity to protect themselves from sexual HIV transmission under their own control. A series of poly[styrene-alt-(maleic anhydride)] derivatives were prepared by amidation or hydrolysis of the anhydride moiety. The derivatives were shown to be of low cell toxicity and effectively inhibited HIV-1 infections in an in vitro cellular model. Poly[styrene-alt-(maleic acid, sodium salt)] was the most potent inhibitor, being 100-fold more potent than dextran sulfate suggesting its potential application as a new class of polyanionic microbicides. [Copyright &y& Elsevier]

[Display omitted] Siglecs that binds cell surface sialoglycans are a family of immunomodulatory receptors, of which, Siglec-7 expressed on natural killer (NK) cells promotes tumor immunoevation while the role of Siglec-1 expressed on macrophages on tumor development remains largely unexplored. Herein, we selectively introduced high affinity sialoside ligands of Siglec-1 and Siglec-7 to tumor cell surface via in vivo Strain-promoted Azide-Alkyne cyclization of TCCSiaα2,3-Lactose or FITCSiaα2,6-Lactose with 9-azido sialic acid (AzSia) metabolically installed on tumor cell surface. We found that TCCSiaα2,3-Lactose conjugated on tumor surface moderately inhibited tumor growth while FITCSiaα2,6-Lactose promote tumor growth. These results suggest high-affinity ligand of Siglec-1 dispalyed on tumors surface provide a new perspective for tumor immunotherapy. [ABSTRACT FROM AUTHOR]

Abstract: Rat liver arginase (arginase I) is potently inactivated by diethyl pyrocarbonate, with a second-order rate constant of 113M−1s−1 for the inactivation process at pH 7.0, 25°C. Partial protection from inactivation is provided by the product of the reaction, l-ornithine, while nearly complete protection is afforded by the inhibitor pair, l-ornithine and borate. The role of H141 has been probed by mutagenesis, chemical modulation, and X-ray diffraction. The hyper-reactivity of H141 towards diethyl pyrocarbonate can be explained by its proximity to E277. A proton shuttling role for H141 is supported by its conformational mobility observed among the known arginase structures. H141 is proposed to serve as an acid/base catalyst, deprotonating the metal-bridging water molecule to generate the metal-bridging hydroxide nucleophile, and by protonating the amino group of the product to facilitate its departure. [Copyright &y& Elsevier]

Arginase is a manganese metalloenzyme that catalyzes the hydrolysis of L-arginine to form L-ornithine and urea. The structure and stability of the binuclear manganese cluster are critical for catalytic activity as it activates the catalytic nucleophile, metal-bridging hydroxide ion, and stabilizes the tetrahedral intermediate and its flanking states. Here, we report X-ray structures of a series of inhibitors bound to the active site of arginase, and each inhibitor exploits a different mode of coordination with the Mn2+2 cluster. Specifically, we have studied the binding of fluoride ion (F-; an uncompetitive inhibitor) and L-arginine, L-valine, dinor-Nω descarboxy-nor-Nω-hydroxy-L-arginine, and dehydro-2(S)-amino- 6-boronohexanoic acid. Some inhibitors, such as fluoride ion, dinor-Nω-hydroxy-L-arginine, and dehydro- 2(S).-amino-6-boronohexanoic acid, cause the net addition of one ligand to the Mn2+2 cluster. Other inhibitors, such as descarboxy-nor-Nω-hydroxy-L-arginine, simply displace the metal-bridging hydroxide ion of the native enzyme and do not cause any net change in the metal coordination polyhedra. The highest affinity inhibitors displace the metal-bridging hydroxide ion (and sometimes occupy a Mn2+A site found vacant in the native enzyme) and maintain a conserved array of hydrogen bonds with their a-amino and -carboxylate groups. [ABSTRACT FROM AUTHOR]

Abstract: Cy-Cl, a cationic near-infrared cyanine dye, readily reacts with hydrogen sulfide (H2S) via nucleophilic thiolation to give dose-dependent ‘turn-off’ fluorescence and colorimetric read-out, allowing selective detection of low levels of H2S in serum and imaging of mitochondrial H2S in living cells. [Copyright &y& Elsevier]

Alteration of lysosome acidity has been implicated in many biological events ranging from apoptosis to cancer metastasis, etc.Mesoporous silica nanoparticles doped with acid activable rhodamine-lactam and fluorescein isothiocyanate (FITC) were developed for ratiometric sensing of lysosomal pH changes in live cells with flow cytometry. [ABSTRACT FROM AUTHOR]

Sialic acid (Sia) residues on cell surface are critical for myriad cellular events such as immunity and inflammation. We herein reported the use of abiotic Sia to raise the thresholds of inflammatory cell responses. Identified from a panel of structurally diversified Sia analogs via a cell inflammation assay, Sia-2, with N-butyryl moiety at C-5, markedly lowered LPS-stimulated NF-κB activity in macrophages. Further analysis shows that Sia-2 attenuates phosphorylation of IκB and Erk1/2/p38/JNK, critical for NF-κB signaling and MAPK signaling, and lowers gene transcription of proinflammatory interleukin-6. These results support the use of abiotic Sia as promising agents to modulate cell surface Sia-pertinent cell signaling. [ABSTRACT FROM AUTHOR]