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Fujiwara T, Mano E, Nango E. Structural basis for the minimal bifunctional alginate epimerase AlgE3 from Azotobacter chroococcum. FEBS Lett 2024; 598:1422-1437. [PMID: 38649293 DOI: 10.1002/1873-3468.14886] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/23/2024] [Revised: 03/15/2024] [Accepted: 03/23/2024] [Indexed: 04/25/2024]
Abstract
Among the epimerases specific to alginate, some of them in Azotobacter genera convert β-d-mannuronic acid to α-l-guluronic acid but also have lyase activity to degrade alginate. The remarkable characteristics of these epimerases make it a promising enzyme for tailoring alginates to meet specific demands. Here, we determined the structure of the bifunctional mannuronan C-5 epimerase AlgE3 from Azotobacter chroococcum (AcAlgE3) in complex with several mannuronic acid oligomers as well as in apo form, which allowed us to elucidate the binding manner of each mannuronic acid oligomer, and the structural plasticity, which is dependent on calcium ions. Moreover, a comprehensive analysis of the lyase activity profiles of AcAlgE3 combined with structural characteristics explained the preference for different chain length oligomers.
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Affiliation(s)
- Takaaki Fujiwara
- Institute of Multidisciplinary Research for Advanced Materials, Tohoku University, Sendai, Japan
| | - Eriko Mano
- Institute of Multidisciplinary Research for Advanced Materials, Tohoku University, Sendai, Japan
| | - Eriko Nango
- Institute of Multidisciplinary Research for Advanced Materials, Tohoku University, Sendai, Japan
- RIKEN SPring-8 Center, Sayo-gun, Japan
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Gaardløs M, Samsonov SA, Sletmoen M, Hjørnevik M, Sætrom GI, Tøndervik A, Aachmann FL. Insights into the roles of charged residues in substrate binding and mode of action of mannuronan C-5 epimerase AlgE4. Glycobiology 2021; 31:1616-1635. [PMID: 33822050 DOI: 10.1093/glycob/cwab025] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/23/2020] [Revised: 03/10/2021] [Indexed: 01/18/2023] Open
Abstract
Mannuronan C-5 epimerases catalyse the epimerization of monomer residues in the polysaccharide alginate, changing the physical properties of the biopolymer. The enzymes are utilized to tailor alginate to numerous biological functions by alginate-producing organisms. The underlying molecular mechanisms that control the processive movement of the epimerase along the substrate chain is still elusive. To study this, we have used an interdisciplinary approach combining molecular dynamics simulations with experimental methods from mutant studies of AlgE4, where initial epimerase activity and product formation were addressed with NMR spectroscopy, and characteristics of enzyme-substrate interactions were obtained with isothermal titration calorimetry and optical tweezers. Positive charges lining the substrate-binding groove of AlgE4 appear to control the initial binding of poly-mannuronate, and binding also seems to be mediated by both electrostatic and hydrophobic interactions. After the catalytic reaction, negatively charged enzyme residues might facilitate dissociation of alginate from the positive residues, working like electrostatic switches, allowing the substrate to translocate in the binding groove. Molecular simulations show translocation increments of two monosaccharide units before the next productive binding event resulting in MG-block formation, with the epimerase moving with its N-terminus towards the reducing end of the alginate chain. Our results indicate that the charge pair R343-D345 might be directly involved in conformational changes of a loop that can be important for binding and dissociation. The computational and experimental approaches used in this study complement each other, allowing for a better understanding of individual residues' roles in binding and movement along the alginate chains.
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Affiliation(s)
- Margrethe Gaardløs
- Norwegian Biopolymer Laboratory (NOBIPOL), Department of Biotechnology and Food Science, NTNU Norwegian University of Science and Technology, Sem Sælands vei 6/8, N-7491 Trondheim, Norway
| | | | - Marit Sletmoen
- Norwegian Biopolymer Laboratory (NOBIPOL), Department of Biotechnology and Food Science, NTNU Norwegian University of Science and Technology, Sem Sælands vei 6/8, N-7491 Trondheim, Norway
| | - Maya Hjørnevik
- Norwegian Biopolymer Laboratory (NOBIPOL), Department of Biotechnology and Food Science, NTNU Norwegian University of Science and Technology, Sem Sælands vei 6/8, N-7491 Trondheim, Norway
| | - Gerd Inger Sætrom
- Norwegian Biopolymer Laboratory (NOBIPOL), Department of Biotechnology and Food Science, NTNU Norwegian University of Science and Technology, Sem Sælands vei 6/8, N-7491 Trondheim, Norway
| | - Anne Tøndervik
- Department of Biotechnology and Nanomedicine, SINTEF Industry, Richard Birkelands veg 3 B, N-7491 Trondheim, Norway
| | - Finn Lillelund Aachmann
- Norwegian Biopolymer Laboratory (NOBIPOL), Department of Biotechnology and Food Science, NTNU Norwegian University of Science and Technology, Sem Sælands vei 6/8, N-7491 Trondheim, Norway
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Håti AG, Aachmann FL, Stokke BT, Skjåk-Bræk G, Sletmoen M. Energy Landscape of Alginate-Epimerase Interactions Assessed by Optical Tweezers and Atomic Force Microscopy. PLoS One 2015; 10:e0141237. [PMID: 26496653 PMCID: PMC4619708 DOI: 10.1371/journal.pone.0141237] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/24/2015] [Accepted: 10/05/2015] [Indexed: 11/28/2022] Open
Abstract
Mannuronan C-5 epimerases are a family of enzymes that catalyze epimerization of alginates at the polymer level. This group of enzymes thus enables the tailor-making of various alginate residue sequences to attain various functional properties, e.g. viscosity, gelation and ion binding. Here, the interactions between epimerases AlgE4 and AlgE6 and alginate substrates as well as epimerization products were determined. The interactions of the various epimerase–polysaccharide pairs were determined over an extended range of force loading rates by the combined use of optical tweezers and atomic force microscopy. When studying systems that in nature are not subjected to external forces the access to observations obtained at low loading rates, as provided by optical tweezers, is a great advantage since the low loading rate region for these systems reflect the properties of the rate limiting energy barrier. The AlgE epimerases have a modular structure comprising both A and R modules, and the role of each of these modules in the epimerization process were examined through studies of the A- module of AlgE6, AlgE6A. Dynamic strength spectra obtained through combination of atomic force microscopy and the optical tweezers revealed the existence of two energy barriers in the alginate-epimerase complexes, of which one was not revealed in previous AFM based studies of these complexes. Furthermore, based on these spectra estimates of the locations of energy transition states (xβ), lifetimes in the absence of external perturbation (τ0) and free energies (ΔG#) were determined for the different epimerase–alginate complexes. This is the first determination of ΔG# for these complexes. The values determined were up to 8 kBT for the outer barrier, and smaller values for the inner barriers. The size of the free energies determined are consistent with the interpretation that the enzyme and substrate are thus not tightly locked at all times but are able to relocate. Together with the observed different affinities determined for AlgE4-polymannuronic acid (poly-M) and AlgE4-polyalternating alginate (poly-MG) macromolecular pairs these data give important contribution to the growing understanding of the mechanisms underlying the processive mode of these enzymes.
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Affiliation(s)
- Armend Gazmeno Håti
- Biophysics and Medical Technology, Dept. of Physics, Norwegian University of Science and Technology, NO-7491, Trondheim, Norway
| | - Finn Lillelund Aachmann
- NOBIPOL, Dept. of Biotechnology, Norwegian University of Science and Technology, NO-7491, Trondheim, Norway
| | - Bjørn Torger Stokke
- Biophysics and Medical Technology, Dept. of Physics, Norwegian University of Science and Technology, NO-7491, Trondheim, Norway
| | - Gudmund Skjåk-Bræk
- NOBIPOL, Dept. of Biotechnology, Norwegian University of Science and Technology, NO-7491, Trondheim, Norway
| | - Marit Sletmoen
- NOBIPOL, Dept. of Biotechnology, Norwegian University of Science and Technology, NO-7491, Trondheim, Norway
- * E-mail:
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Beatson R, Maurstad G, Picco G, Arulappu A, Coleman J, Wandell HH, Clausen H, Mandel U, Taylor-Papadimitriou J, Sletmoen M, Burchell JM. The Breast Cancer-Associated Glycoforms of MUC1, MUC1-Tn and sialyl-Tn, Are Expressed in COSMC Wild-Type Cells and Bind the C-Type Lectin MGL. PLoS One 2015; 10:e0125994. [PMID: 25951175 PMCID: PMC4423978 DOI: 10.1371/journal.pone.0125994] [Citation(s) in RCA: 66] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/06/2015] [Accepted: 03/27/2015] [Indexed: 11/19/2022] Open
Abstract
Aberrant glycosylation occurs in the majority of human cancers and changes in mucin-type O-glycosylation are key events that play a role in the induction of invasion and metastases. These changes generate novel cancer-specific glyco-antigens that can interact with cells of the immune system through carbohydrate binding lectins. Two glyco-epitopes that are found expressed by many carcinomas are Tn (GalNAc-Ser/Thr) and STn (NeuAcα2,6GalNAc-Ser/Thr). These glycans can be carried on many mucin-type glycoproteins including MUC1. We show that the majority of breast cancers carry Tn within the same cell and in close proximity to extended glycan T (Galβ1,3GalNAc) the addition of Gal to the GalNAc being catalysed by the T synthase. The presence of active T synthase suggests that loss of the private chaperone for T synthase, COSMC, does not explain the expression of Tn and STn in breast cancer cells. We show that MUC1 carrying both Tn or STn can bind to the C-type lectin MGL and using atomic force microscopy show that they bind to MGL with a similar dead adhesion force. Tumour associated STn is associated with poor prognosis and resistance to chemotherapy in breast carcinomas, inhibition of DC maturation, DC apoptosis and inhibition of NK activity. As engagement of MGL in the absence of TLR triggering may lead to anergy, the binding of MUC1-STn to MGL may be in part responsible for some of the characteristics of STn expressing tumours.
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Affiliation(s)
- Richard Beatson
- Breast Cancer Biology, King’s College London, Guy’s Hospital, London, SE1 9RT, United Kingdom
| | - Gjertrud Maurstad
- Department of Physics, Norwegian University of Science and Technology, 7491, Trondheim, Norway
| | - Gianfranco Picco
- Breast Cancer Biology, King’s College London, Guy’s Hospital, London, SE1 9RT, United Kingdom
| | - Appitha Arulappu
- Breast Cancer Biology, King’s College London, Guy’s Hospital, London, SE1 9RT, United Kingdom
| | - Julia Coleman
- Breast Cancer Biology, King’s College London, Guy’s Hospital, London, SE1 9RT, United Kingdom
| | - Hans H. Wandell
- Copenhagen Center for Glycomics, University of Copenhagen, Copenhagen, DK-2200, Denmark
| | - Henrik Clausen
- Copenhagen Center for Glycomics, University of Copenhagen, Copenhagen, DK-2200, Denmark
| | - Ulla Mandel
- Copenhagen Center for Glycomics, University of Copenhagen, Copenhagen, DK-2200, Denmark
| | | | - Marit Sletmoen
- Department of Physics, Norwegian University of Science and Technology, 7491, Trondheim, Norway
| | - Joy M. Burchell
- Breast Cancer Biology, King’s College London, Guy’s Hospital, London, SE1 9RT, United Kingdom
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Buchinger E, Knudsen DH, Behrens MA, Pedersen JS, Aarstad OA, Tøndervik A, Valla S, Skjåk-Bræk G, Wimmer R, Aachmann FL. Structural and functional characterization of the R-modules in alginate C-5 epimerases AlgE4 and AlgE6 from Azotobacter vinelandii. J Biol Chem 2014; 289:31382-96. [PMID: 25266718 DOI: 10.1074/jbc.m114.567008] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023] Open
Abstract
The bacterium Azotobacter vinelandii produces a family of seven secreted and calcium-dependent mannuronan C-5 epimerases (AlgE1-7). These epimerases are responsible for the epimerization of β-D-mannuronic acid (M) to α-L-guluronic acid (G) in alginate polymers. The epimerases display a modular structure composed of one or two catalytic A-modules and from one to seven R-modules having an activating effect on the A-module. In this study, we have determined the NMR structure of the three individual R-modules from AlgE6 (AR1R2R3) and the overall structure of both AlgE4 (AR) and AlgE6 using small angle x-ray scattering. Furthermore, the alginate binding ability of the R-modules of AlgE4 and AlgE6 has been studied with NMR and isothermal titration calorimetry. The AlgE6 R-modules fold into an elongated parallel β-roll with a shallow, positively charged groove across the module. Small angle x-ray scattering analyses of AlgE4 and AlgE6 show an overall elongated shape with some degree of flexibility between the modules for both enzymes. Titration of the R-modules with defined alginate oligomers shows strong interaction between AlgE4R and both oligo-M and MG, whereas no interaction was detected between these oligomers and the individual R-modules from AlgE6. A combination of all three R-modules from AlgE6 shows weak interaction with long M-oligomers. Exchanging the R-modules between AlgE4 and AlgE6 resulted in a novel epimerase called AlgE64 with increased G-block forming ability compared with AlgE6.
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Affiliation(s)
- Edith Buchinger
- From the Department of Biotechnology, Chemistry and Environmental Engineering, Aalborg University, Frederik Bajers vej 7H, DK-9220 Aalborg, Denmark, the Department of Biotechnology, Norwegian Biopolymer Laboratory (NOBIPOL), Norwegian University of Science and Technology, Sem Sælands vei 6/8, 7491 Trondheim, Norway
| | - Daniel H Knudsen
- From the Department of Biotechnology, Chemistry and Environmental Engineering, Aalborg University, Frederik Bajers vej 7H, DK-9220 Aalborg, Denmark
| | - Manja A Behrens
- the Interdisciplinary Nanoscience Center and Department of Chemistry, Aarhus University, Gustav Wieds Vej 14, DK-8000, Denmark, and
| | - Jan Skov Pedersen
- the Interdisciplinary Nanoscience Center and Department of Chemistry, Aarhus University, Gustav Wieds Vej 14, DK-8000, Denmark, and
| | - Olav A Aarstad
- the Department of Biotechnology, Norwegian Biopolymer Laboratory (NOBIPOL), Norwegian University of Science and Technology, Sem Sælands vei 6/8, 7491 Trondheim, Norway
| | - Anne Tøndervik
- the Department of Bioprocess Technology, SINTEF Materials and Chemistry, N-7465 Trondheim, Norway
| | - Svein Valla
- the Interdisciplinary Nanoscience Center and Department of Chemistry, Aarhus University, Gustav Wieds Vej 14, DK-8000, Denmark, and
| | - Gudmund Skjåk-Bræk
- the Department of Biotechnology, Norwegian Biopolymer Laboratory (NOBIPOL), Norwegian University of Science and Technology, Sem Sælands vei 6/8, 7491 Trondheim, Norway
| | - Reinhard Wimmer
- From the Department of Biotechnology, Chemistry and Environmental Engineering, Aalborg University, Frederik Bajers vej 7H, DK-9220 Aalborg, Denmark
| | - Finn L Aachmann
- the Department of Biotechnology, Norwegian Biopolymer Laboratory (NOBIPOL), Norwegian University of Science and Technology, Sem Sælands vei 6/8, 7491 Trondheim, Norway,
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Sletmoen M, Stokke BT. Structure-Function Relationships in Glycopolymers: Effects of Residue Sequences, Duplex, and Triplex Organization. Biopolymers 2013; 99:757-71. [DOI: 10.1002/bip.22320] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/07/2013] [Accepted: 06/07/2013] [Indexed: 12/18/2022]
Affiliation(s)
- Marit Sletmoen
- Biophysics and Medical Technology, Department of Physics, The Norwegian University of Science and Technology; Trondheim; Norway
| | - Bjørn Torger Stokke
- Biophysics and Medical Technology, Department of Physics, The Norwegian University of Science and Technology; Trondheim; Norway
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7
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Molecular recognition force spectroscopy of a specific lectin–carbohydrate interaction at single-molecule level. J Struct Biol 2011; 176:46-51. [DOI: 10.1016/j.jsb.2011.05.018] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/02/2011] [Revised: 05/18/2011] [Accepted: 05/19/2011] [Indexed: 11/19/2022]
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8
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Li Y, Wang J, Xing C, Wang Z, Wang H, Zhang B, Tang J. Molecular Recognition Force Spectroscopy Study of the Specific Lectin and Carbohydrate Interaction in a Living Cell. Chemphyschem 2011; 12:909-12. [DOI: 10.1002/cphc.201001008] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/06/2010] [Revised: 01/29/2011] [Indexed: 01/06/2023]
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9
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Sisquella X, de Pourcq K, Alguacil J, Robles J, Sanz F, Anselmetti D, Imperial S, Fernàndez-Busquets X. A single-molecule force spectroscopy nanosensor for the identification of new antibiotics and antimalarials. FASEB J 2010; 24:4203-17. [PMID: 20634351 DOI: 10.1096/fj.10-155507] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/19/2023]
Abstract
An important goal of nanotechnology is the application of individual molecule handling techniques to the discovery of potential new therapeutic agents. Of particular interest is the search for new inhibitors of metabolic routes exclusive of human pathogens, such as the 2-C-methyl-D-erythritol-4-phosphate (MEP) pathway essential for the viability of most human pathogenic bacteria and of the malaria parasite. Using atomic force microscopy single-molecule force spectroscopy (SMFS), we have probed at the single-molecule level the interaction of 1-deoxy-D-xylulose 5-phosphate synthase (DXS), which catalyzes the first step of the MEP pathway, with its two substrates, pyruvate and glyceraldehyde-3-phosphate. The data obtained in this pioneering SMFS analysis of a bisubstrate enzymatic reaction illustrate the substrate sequentiality in DXS activity and allow for the calculation of catalytic parameters with single-molecule resolution. The DXS inhibitor fluoropyruvate has been detected in our SMFS competition experiments at a concentration of 10 μM, improving by 2 orders of magnitude the sensitivity of conventional enzyme activity assays. The binding of DXS to pyruvate is a 2-step process with dissociation constants of k(off) = 6.1 × 10(-4) ± 7.5 × 10(-3) and 1.3 × 10(-2) ± 1.0 × 10(-2) s(-1), and reaction lengths of x(β) = 3.98 ± 0.33 and 0.52 ± 0.23 Å. These results constitute the first quantitative report on the use of nanotechnology for the biodiscovery of new antimalarial enzyme inhibitors and open the field for the identification of compounds represented only by a few dozens of molecules in the sensor chamber.
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Affiliation(s)
- Xavier Sisquella
- Nanotechnology Platform, Barcelona Science Park, Barcelona, Spain
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Takemasa M, Sletmoen M, Stokke BT. Single molecular pair interactions between hydrophobically modified hydroxyethyl cellulose and amylose determined by dynamic force spectroscopy. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2009; 25:10174-10182. [PMID: 19496550 DOI: 10.1021/la9009515] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/27/2023]
Abstract
Interactions among HMHEC (hydrophobically modified hydroxyethyl cellulose) and between HMHEC and amylose were investigated by means of dynamic force spectroscopy of single molecular pairs. The technique was realized using a scanning probe based platform, and the molecular pair interactions were investigated in aqueous solutions over a range of force loading rates. Both hydrophobic interactions among hydrophobe C(16) alkyl side chains in HMHEC and association between these hydrophobes in HMHEC and amylose showed a stretching type peak. The distribution analysis of rupture force based on Bell-Evans's model revealed that the peaks had a most probable rupture force ranging from 27 pN at a force loading rate r(f) = 0.43 nN/s to 125 pN at r(f) = 170 nN/s for HMHEC-HMHEC, and from 13 pN at r(f) = 0.20 nN/s to 34 pN at r(f) = 33.7 nN/s for HMHEC-amylose interactions. The distance of the energy barrier relative to the minimum, x(beta), and the apparent lifetime in the absence of external force, tau, were found to depend on the force loading rate, and the average values are estimated to be 0.99 nm and 0.89s for HMHEC-HMHEC and 0.31 nm and 0.075s for HMHEC-amylose interactions. The obtained data for these pairwise molecular interactions are underpinning the associative behavior of the macroscopic properties of aqueous solutions of these polysaccharides.
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Affiliation(s)
- Makoto Takemasa
- Biophysics and Medical Technology, Department of Physics, The Norwegian University of Science and Technology, NTNU, NO-7491 Trondheim, Norway
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11
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Wilner O, Guidotti C, Wieckowska A, Gill R, Willner I. Probing Kinase Activities by Electrochemistry, Contact-Angle Measurements, and Molecular-Force Interactions. Chemistry 2008; 14:7774-81. [DOI: 10.1002/chem.200800765] [Citation(s) in RCA: 45] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
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12
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Gil R, Guillerez MG, Poulin JC, Schulz E. Charge-transfer complex study by chemical force spectroscopy: a dynamic force spectroscopic approach. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2007; 23:542-8. [PMID: 17209605 DOI: 10.1021/la062169h] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/13/2023]
Abstract
Charge-transfer interaction, as a reversible and rapid phenomenon, was evidenced by force microscopy. Pull-off forces were measured between a tip grafted with a trinitrofluorenone derivative and a surface functionalized with an electron-rich aromatic anthracene compound in a dodecane environment. The effect of the sweep time on the measured interaction forces is described, together with an extensive study of a competitive influence of free aromatic molecules in dodecane diluted solutions. These forces depend on the nature of the competitor and its concentration as well as on the velocity of tip/sample separation.
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Affiliation(s)
- Richard Gil
- Equipe Catalyse Moléculaire, Institut de Chimie Moléculaire et des Matériaux d'Orsay, UMR 8182, Université Paris-Sud, Bât 420, 91405 Orsay Cedex, France
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Holtan S, Bruheim P, Skjåk-Bræk G. Mode of action and subsite studies of the guluronan block-forming mannuronan C-5 epimerases AlgE1 and AlgE6. Biochem J 2006; 395:319-29. [PMID: 16390328 PMCID: PMC1422759 DOI: 10.1042/bj20051804] [Citation(s) in RCA: 35] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
AlgE1, AlgE5 and AlgE6 are members of a family of mannuronan C-5 epimerases encoded by the bacterium Azotobacter vinelandii, and are active in the biosynthesis of alginate, where they catalyse the post-polymerization conversion of beta-D-mannuronic acid (M) residues into alpha-L-guluronic acid residues (G). All enzymes show preference for introducing G-residues neighbouring a pre-existing G. They also have the capacity to convert single M residues flanked by G, thus 'condensing' G-blocks to form almost homopolymeric guluronan. Analysis of the length and distribution of G-blocks based on specific enzyme degradation combined with size-exclusion chromatography, electrospray ionization MS, HPAEC-PAD (high-performance anion-exchange chromatography and pulsed amperometric detection), MALDI (matrix-assisted laser-desorption ionization)-MS and NMR revealed large differences in block length and distribution generated by AlgE1 and AlgE6, probably reflecting their different degree of processivity. When acting on polyMG as substrates, AlgE1 initially forms only long homopolymeric G-blocks >50, while AlgE6 gives shorter blocks with a broader block size distribution. Analyses of the AlgE1 and AlgE6 subsite specificities by the same methodology showed that a mannuronan octamer and heptamer respectively were the minimum substrate chain lengths needed to accommodate enzyme activities. The fourth M residue from the non-reducing end is epimerized first by both enzymes. When acting on MG-oligomers, AlgE1 needed a decamer while AlgE6 an octamer to accommodate activity. By performing FIA (flow injection analysis)-MS on the lyase digests of epimerized and standard MG-oligomers, the M residue in position 5 from the non-reducing end was preferentially attacked by both enzymes, creating an MGMGGG-sequence (underlined and boldface indicate the epimerized residue).
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Affiliation(s)
- Synnøve Holtan
- *Norwegian Biopolymer Laboratory, Department of Biotechnology, The Norwegian University of Science and Technology (NTNU), Trondheim, Norway
| | - Per Bruheim
- †SINTEF Materials and Chemistry, Sem Sælands vei 6/8, N-7491 Trondheim, Norway
| | - Gudmund Skjåk-Bræk
- *Norwegian Biopolymer Laboratory, Department of Biotechnology, The Norwegian University of Science and Technology (NTNU), Trondheim, Norway
- To whom correspondence should be addressed (email )
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