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      Supramolecular Assemblies of a Conjugate of Nucleobase, Amino Acids, and Saccharide Act as Agonists for Proliferation of Embryonic Stem Cells and Development of Zygotes

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          Abstract

          The synthetic challenges in glycobiology and glycochemistry hamper the development of glycobiomaterials for biomedicine. Here we report the use of molecular self-assembly to sidestep the laborious synthesis of complex glycans for promoting the proliferation of murine embryonic stem (mES) cells. Our study shows that the supramolecular assemblies of a small molecule conjugate of nucleobase, amino acids, and saccharide, as a de novo glycoconjugate, promote the proliferation of mES cells and the development of zygotes into blastocysts of mouse. Molecular engineering confirms that each motif (i.e., adenine, Arg-Gly-Asp (RGD) domain, and glucosamine) is indispensable for the observed activity of the conjugate. As the first example of using assemblies of the molecular conjugates of multiple fundamental biological building blocks to control cell behaviors, this work illustrates an unprecedented approach to use supramolecular assemblies as multifunctional mimics of glycoconjugates.

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          Rapid planetesimal formation in turbulent circumstellar discs

          The initial stages of planet formation in circumstellar gas discs proceed via dust grains that collide and build up larger and larger bodies (Safronov 1969). How this process continues from metre-sized boulders to kilometre-scale planetesimals is a major unsolved problem (Dominik et al. 2007): boulders stick together poorly (Benz 2000), and spiral into the protostar in a few hundred orbits due to a head wind from the slower rotating gas (Weidenschilling 1977). Gravitational collapse of the solid component has been suggested to overcome this barrier (Safronov 1969, Goldreich & Ward 1973, Youdin & Shu 2002). Even low levels of turbulence, however, inhibit sedimentation of solids to a sufficiently dense midplane layer (Weidenschilling & Cuzzi 1993, Dominik et al. 2007), but turbulence must be present to explain observed gas accretion in protostellar discs (Hartmann 1998). Here we report the discovery of efficient gravitational collapse of boulders in locally overdense regions in the midplane. The boulders concentrate initially in transient high pressures in the turbulent gas (Johansen, Klahr, & Henning 2006), and these concentrations are augmented a further order of magnitude by a streaming instability (Youdin & Goodman 2005, Johansen, Henning, & Klahr 2006, Johansen & Youdin 2007) driven by the relative flow of gas and solids. We find that gravitationally bound clusters form with masses comparable to dwarf planets and containing a distribution of boulder sizes. Gravitational collapse happens much faster than radial drift, offering a possible path to planetesimal formation in accreting circumstellar discs.
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            RGD and other recognition sequences for integrins.

            Proteins that contain the Arg-Gly-Asp (RGD) attachment site, together with the integrins that serve as receptors for them, constitute a major recognition system for cell adhesion. The RGD sequence is the cell attachment site of a large number of adhesive extracellular matrix, blood, and cell surface proteins, and nearly half of the over 20 known integrins recognize this sequence in their adhesion protein ligands. Some other integrins bind to related sequences in their ligands. The integrin-binding activity of adhesion proteins can be reproduced by short synthetic peptides containing the RGD sequence. Such peptides promote cell adhesion when insolubilized onto a surface, and inhibit it when presented to cells in solution. Reagents that bind selectively to only one or a few of the RGD-directed integrins can be designed by cyclizing peptides with selected sequences around the RGD and by synthesizing RGD mimics. As the integrin-mediated cell attachment influences and regulates cell migration, growth, differentiation, and apoptosis, the RGD peptides and mimics can be used to probe integrin functions in various biological systems. Drug design based on the RGD structure may provide new treatments for diseases such as thrombosis, osteoporosis, and cancer.
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              Versatile Photocatalytic Systems for H2 Generation in Water Based on an Efficient DuBois-Type Nickel Catalyst

              The generation of renewable H2 through an efficient photochemical route requires photoinduced electron transfer (ET) from a light harvester to an efficient electrocatalyst in water. Here, we report on a molecular H2 evolution catalyst (NiP) with a DuBois-type [Ni(P2 R′N2 R″)2]2+ core (P2 R′N2 R″ = bis(1,5-R′-diphospha-3,7-R″-diazacyclooctane), which contains an outer coordination sphere with phosphonic acid groups. The latter functionality allows for good solubility in water and immobilization on metal oxide semiconductors. Electrochemical studies confirm that NiP is a highly active electrocatalyst in aqueous electrolyte solution (overpotential of approximately 200 mV at pH 4.5 with a Faradaic yield of 85 ± 4%). Photocatalytic experiments and investigations on the ET kinetics were carried out in combination with a phosphonated Ru(II) tris(bipyridine) dye (RuP) in homogeneous and heterogeneous environments. Time-resolved luminescence and transient absorption spectroscopy studies confirmed that directed ET from RuP to NiP occurs efficiently in all systems on the nano- to microsecond time scale, through three distinct routes: reductive quenching of RuP in solution or on the surface of ZrO2 (“on particle” system) or oxidative quenching of RuP when the compounds were immobilized on TiO2 (“through particle” system). Our studies show that NiP can be used in a purely aqueous solution and on a semiconductor surface with a high degree of versatility. A high TOF of 460 ± 60 h–1 with a TON of 723 ± 171 for photocatalytic H2 generation with a molecular Ni catalyst in water and a photon-to-H2 quantum yield of approximately 10% were achieved for the homogeneous system.
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                Author and article information

                Journal
                Bioconjug Chem
                Bioconjug. Chem
                bc
                bcches
                Bioconjugate Chemistry
                American Chemical Society
                1043-1802
                1520-4812
                05 May 2014
                18 June 2014
                : 25
                : 6
                : 1031-1035
                Affiliations
                [1]Department of Chemistry, Brandeis University , 415 South Street, Waltham, Massachusetts 02454, United States
                [2]Department of Pharmaceutical Sciences, University of New England College of Pharmacy , 716 Stevens Avenue, Portland, Maine 04102, United States
                Author notes
                Article
                10.1021/bc500187m
                4068792
                24798034
                9127c80d-61e7-4326-bb83-798c27a7c8af
                Copyright © 2014 American Chemical Society

                Terms of Use

                History
                : 25 April 2014
                Funding
                National Institutes of Health, United States
                Categories
                Communication
                Custom metadata
                bc500187m
                bc-2014-00187m

                Biochemistry
                Biochemistry

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