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Abstract: SNi-like mechanisms, which involve front-face leaving group departure and nucleophile approach, have been observed experimentally and computationally in chemical and enzymatic substitution at α-glycosyl electrophiles. Since SNi-like, SN1 and SN2 substitution pathways can be energetically comparable, engineered switching could be feasible. Here, engineering of Sulfolobus solfataricus β-glycosidase, which originally catalyzed double SN2 substitution, changed its mode to SNi-like. Destruction of the first SN2 nucleophile through E387Y mutation created a β-stereoselective catalyst for glycoside synthesis from activated substrates, despite lacking a nucleophile. The pH profile, kinetic and mutational analyses, mechanism-based inactivators, X-ray structure and subsequent metadynamics simulations together suggest recruitment of substrates by π–sugar interaction and reveal a quantum mechanics–molecular mechanics (QM/MM) free-energy landscape for the substitution reaction that is similar to those of natural, SNi-like glycosyltransferases. This observation of a front-face mechanism in a β-glycosyltransfer enzyme highlights that SNi-like pathways may be engineered in catalysts with suitable environments and suggests that 'β-SNi' mechanisms may be feasible for natural glycosyltransfer enzymes.
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Jun 2017
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I02-Macromolecular Crystallography
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Yi
Jin
,
Marija
Petricevic
,
Alan
John
,
Lluís
Raich
,
Huw
Jenkins
,
Leticia
Portela De Souza
,
Fiona
Cuskin
,
Harry J.
Gilbert
,
Carme
Rovira
,
Ethan D.
Goddard-borger
,
Spencer J.
Williams
,
Gideon J.
Davies
Diamond Proposal Number(s):
[9948]
Abstract: The enzymatic cleavage of β-1,4-mannans is achieved by endo-β-1,4-mannanases, enzymes involved in germination of seeds and microbial hemicellulose degradation, and which have increasing industrial and consumer product applications. β-Mannanases occur in a range of families of the CAZy sequence-based glycoside hydrolase (GH) classification scheme including families 5, 26, and 113. In this work we reveal that β-mannanases of the newly described GH family 134 differ from other mannanase families in both their mechanism and tertiary structure. A representative GH family 134 endo-β-1,4-mannanase from a Streptomyces sp. displays a fold closely related to that of hen egg white lysozyme but acts with inversion of stereochemistry. A Michaelis complex with mannopentaose, and a product complex with mannotriose, reveal ligands with pyranose rings distorted in an unusual inverted chair conformation. Ab initio quantum mechanics/molecular mechanics metadynamics quantified the energetically accessible ring conformations and provided evidence in support of a 1C4 → 3H4‡ → 3S1 conformational itinerary along the reaction coordinate. This work, in concert with that on GH family 124 cellulases, reveals how the lysozyme fold can be co-opted to catalyze the hydrolysis of different polysaccharides in a mechanistically distinct manner.
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Nov 2016
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I02-Macromolecular Crystallography
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Thomas J. M.
Beenakker
,
Dennis P. A.
Wander
,
Wendy
Offen
,
Marta
Artola
,
Lluís
Raich
,
Maria J.
Ferraz
,
Kah-yee
Li
,
Judith H. P. M.
Houben
,
Erwin R.
Van Rijssel
,
Thomas
Hansen
,
Gijsbert A.
Van Der Marel
,
Jeroen D. C.
Codée
,
Johannes M. F. G.
Aerts
,
Carme
Rovira
,
Gideon J.
Davies
,
Herman S.
Overkleeft
Diamond Proposal Number(s):
[13587]
Abstract: The conformational analysis of glycosidases affords a route to their specific inhibition through transition-state mimicry. Inspired by the rapid reaction rates of cyclophellitol and cyclophellitol aziridine—both covalent retaining β-glucosidase inhibitors—we postulated that the corresponding carba “cyclopropyl” analogue would be a potent retaining β-glucosidase inhibitor for those enzymes reacting through the 4H3 transition-state conformation. Ab initio metadynamics simulations of the conformational free energy landscape for the cyclopropyl inhibitors show a strong bias for the 4H3 conformation, and carba-cyclophellitol, with an N-(4-azidobutyl)carboxamide moiety, proved to be a potent inhibitor (Ki = 8.2 nM) of the Thermotoga maritima TmGH1 β-glucosidase. 3-D structural analysis and comparison with unreacted epoxides show that this compound indeed binds in the 4H3 conformation, suggesting that conformational strain induced through a cyclopropyl unit may add to the armory of tight-binding inhibitor designs.
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May 2017
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I02-Macromolecular Crystallography
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Open Access
Abstract: The enzymatic hydrolysis of α-l-fucosides is of importance in cancer, bacterial infections, and fucosidosis, a neurodegenerative lysosomal storage disorder. Here we show a series of snapshots along the reaction coordinate of a glycoside hydrolase family GH29 α-l-fucosidase unveiling a Michaelis (ES) complex in a 1C4 (chair) conformation and a covalent glycosyl-enzyme intermediate in 3S1 (skew-boat). First principles metadynamics simulations on isolated α-l-fucose strongly support a 1C4↔3H4↔3S1 conformational itinerary for the glycosylation step of the reaction mechanism and indicate a strong “preactivation” of the 1C4 complex to nucleophilic attack as reflected by free energy, C1−O1/O5−C1 bond length elongation/reduction, C1−O1 bond orientation, and positive charge development around the anomeric carbon. Analysis of an imino sugar inhibitor is consistent with tight binding of a chair-conformed charged species.
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Feb 2010
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I02-Macromolecular Crystallography
I03-Macromolecular Crystallography
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Rohan J.
Williams
,
Javier
Iglesias-fernández
,
Judith
Stepper
,
Adam
Jackson
,
Andrew
Thompson
,
Elisabeth C.
Lowe
,
John
White
,
Harry J.
Gilbert
,
Carme
Rovira
,
Gideon J.
Davies
,
Spencer J.
Williams
Diamond Proposal Number(s):
[7864]
Abstract: Mannosidases catalyze the hydrolysis of a diverse range of polysaccharides and glycoconjugates, and the various sequence-based mannosidase families have evolved ingenious strategies to overcome the stereoelectronic challenges of mannoside chemistry. Using a combination of computational chemistry, inhibitor design and synthesis, and X-ray crystallography of inhibitor/enzyme complexes, it is demonstrated that mannoimidazole-type inhibitors are energetically poised to report faithfully on mannosidase transition-state conformation, and provide direct evidence for the conformational itinerary used by diverse mannosidases, including β-mannanases from families GH26 and GH113. Isofagomine-type inhibitors are poor mimics of transition-state conformation, owing to the high energy barriers that must be crossed to attain mechanistically relevant conformations, however, these sugar-shaped heterocycles allow the acquisition of ternary complexes that span the active site, thus providing valuable insight into active-site residues involved in substrate recognition.
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Jan 2014
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I02-Macromolecular Crystallography
I04-1-Macromolecular Crystallography (fixed wavelength)
I04-Macromolecular Crystallography
I24-Microfocus Macromolecular Crystallography
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Marija
Petricevic
,
Lukasz F.
Sobala
,
Pearl
Fernandes
,
Lluís
Raich
,
Andrew James
Thompson
,
Ganeko
Bernardo-seisdedos
,
Oscar
Millet
,
Sha
Zhu
,
Matthieu
Sollogoub
,
Jesús
Jimenez-barbero
,
Carme
Rovira
,
Gideon J.
Davies
,
Spencer J.
Williams
Diamond Proposal Number(s):
[9948]
Abstract: Inhibitor design incorporating features of the reaction coordinate and transition-state structure has emerged as a powerful approach for the development of enzyme inhibitors. Such inhibitors find use as mechanistic probes, chemical biology tools and therapeutics. Endo-α-1,2-mannosidases and endo-α-1,2-mannanases, members of glycoside hydrolase family 99 (GH99), are interesting targets for inhibitor development as they play key roles in N-glycan maturation and microbiotal yeast mannan degradation, respectively. These enzymes are proposed to act via an 1,2-anhydrosugar 'epoxide' mechanism that proceeds through a proposed unusual conformational itinerary. Here, we explore how charge and shape contribute to binding of diverse inhibitors of these enzymes. We report the synthesis of neutral dideoxy, glucal and cyclohexenyl disaccharide inhibitors, their binding to GH99 endo-α-1,2-mannanases, and their structural analysis by X-ray crystallography. Quantum mechanical calculations of the free energy landscapes reveal how the neutral inhibitors provide shape but not charge mimicry of the proposed intermediate and transition state structures. Building upon the knowledge of shape and charge contributions to inhibition of family GH99 enzymes, we design and synthesize α-Man-1,3-noeuromycin, which is revealed to be the most potent (KD 13 nM for Bacteroides xylanisolvens GH99 enzyme) inhibitor of these enzymes yet reported. This work reveals how shape and charge mimicry of transition state features can enable the rational design of potent inhibitors.
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Dec 2016
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I02-Macromolecular Crystallography
I04-Macromolecular Crystallography
|
Diamond Proposal Number(s):
[13587]
Abstract: Conformational analysis of enzyme-catalyzed mannoside hydrolysis has revealed two predominant conformational itineraries through B2,5 or 3H4 transition-state (TS) conformations. A prominent unassigned catalytic itinerary is that of exo-1,6-α-mannosidases belonging to CAZy family 125. A published complex of Clostridium perfringens GH125 enzyme with a nonhydrolyzable 1,6-α-thiomannoside substrate mimic bound across the active site revealed an undistorted 4C1 conformation and provided no insight into the catalytic pathway of this enzyme. We show through a purely computational approach (QM/MM metadynamics) that sulfur-for-oxygen substitution in the glycosidic linkage fundamentally alters the energetically accessible conformational space of a thiomannoside when bound within the GH125 active site. Modeling of the conformational free energy landscape (FEL) of a thioglycoside strongly favors a mechanistically uninformative 4C1 conformation within the GH125 enzyme active site, but the FEL of corresponding O-glycoside substrate reveals a preference for a Michaelis complex in an OS2 conformation (consistent with catalysis through a B2,5 TS). This prediction was tested experimentally by determination of the 3D X-ray structure of the pseudo-Michaelis complex of an inactive (D220N) variant of C. perfringens GH125 enzyme in complex with 1,6-α-mannobiose. This complex revealed unambiguous distortion of the −1 subsite mannoside to an OS2 conformation, matching that predicted by theory and supporting an OS2 → B2,5 → 1S5 conformational itinerary for GH125 α-mannosidases. This work highlights the power of the QM/MM approach and identified shortcomings in the use of nonhydrolyzable substrate analogues for conformational analysis of enzyme-bound species.
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Jan 2017
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I02-Macromolecular Crystallography
I04-Macromolecular Crystallography
|
Marta
Artola
,
Liang
Wu
,
Maria J.
Ferraz
,
Chi-lin
Kuo
,
Lluís
Raich
,
Imogen Z.
Breen
,
Wendy A.
Offen
,
Jeroen D. C.
Codée
,
Gijsbert A.
Van Der Marel
,
Carme
Rovira
,
Johannes M. F. G.
Aerts
,
Gideon J.
Davies
,
Herman S.
Overkleeft
Diamond Proposal Number(s):
[13587]
Open Access
Abstract: The essential biological roles played by glycosidases, coupled to the diverse therapeutic benefits of pharmacologically targeting these enzymes, provide considerable motivation for the development of new inhibitor classes. Cyclophellitol epoxides and aziridines are recently established covalent glycosidase inactivators. Inspired by the application of cyclic sulfates as electrophilic equivalents of epoxides in organic synthesis, we sought to test whether cyclophellitol cyclosulfates would similarly act as irreversible glycosidase inhibitors. Here we present the synthesis, conformational analysis, and application of novel 1,6-cyclophellitol cyclosulfates. We show that 1,6-epi-cyclophellitol cyclosulfate (α-cyclosulfate) is a rapidly reacting α-glucosidase inhibitor whose 4C1 chair conformation matches that adopted by α-glucosidase Michaelis complexes. The 1,6-cyclophellitol cyclosulfate (β-cyclosulfate) reacts more slowly, likely reflecting its conformational restrictions. Selective glycosidase inhibitors are invaluable as mechanistic probes and therapeutic agents, and we propose cyclophellitol cyclosulfates as a valuable new class of carbohydrate mimetics for application in these directions.
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Jul 2017
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|
I02-Macromolecular Crystallography
I04-Macromolecular Crystallography
|
Marta
Artola
,
Christinne
Hedberg
,
Rhianna J.
Rowland
,
Lluís
Raich
,
Kassiani
Kytidou
,
Liang
Wu
,
Amanda
Schaaf
,
Maria Joao
Ferraz
,
Gijsbert A.
Van Der Marel
,
Jeroen D. C.
Codée
,
Carme
Rovira
,
Johannes M. F. G.
Aerts
,
Gideon J.
Davies
,
Herman S.
Overkleeft
Diamond Proposal Number(s):
[13587]
Open Access
Abstract: Fabry disease is an inherited lysosomal storage disorder that is characterized by a deficiency in lysosomal α-D-galactosidase activity. One current therapeutic strategy involves enzyme replacement therapy, in which patients are treated with a recombinant enzyme. Co-treatment with enzyme active-site stabilizers is advocated to increase treatment efficacy, a strategy that requires effective and selective enzyme stabilizers. Here, we describe the design and development of an α-D-gal-cyclophellitol cyclosulfamidate as a new class of neutral, conformationally constrained competitive glycosidase inhibitors that act by mimicry of the Michaelis complex conformation. We found that D-galactose-configured α-cyclosulfamidate 4 effectively stabilizes recombinant human α-D-galactosidase (agalsidase beta, Fabrazyme®) both in vitro and in cellulo.
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Aug 2019
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I02-Macromolecular Crystallography
I04-Macromolecular Crystallography
|
Diamond Proposal Number(s):
[13587]
Abstract: The non-hydrolyzable S-linked azasugars, 1,6-α-mannosylthio- and 1,6-α-mannobiosylthioisofagomine, were synthesized and shown to bind with high affinity to a family 76 endo-1,6-α-mannanase from Bacillus circulans. X-ray crystallography showed an atypical interaction of the isofagomine nitrogen with the catalytic acid/base. Molecular dynamics simulations reveal that the atypical binding results from sulfur perturbing the most stable form away from the nucleophile interaction preferred for the O-linked congener.
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Jul 2017
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