Publications by authors named "Nicholas G S McGregor"

4 Publications

  • Page 1 of 1

Cysteine Nucleophiles in Glycosidase Catalysis: Application of a Covalent β-l-Arabinofuranosidase Inhibitor.

Angew Chem Int Ed Engl 2021 03 2;60(11):5754-5758. Epub 2021 Feb 2.

York Structural Biology Laboratory, Department of Chemistry, The University of York, Heslington, York, YO10 5DD, UK.

The recent discovery of zinc-dependent retaining glycoside hydrolases (GHs), with active sites built around a Zn(Cys) (Glu) coordination complex, has presented unresolved mechanistic questions. In particular, the proposed mechanism, depending on a Zn-coordinated cysteine nucleophile and passing through a thioglycosyl enzyme intermediate, remains controversial. This is primarily due to the expected stability of the intermediate C-S bond. To facilitate the study of this atypical mechanism, we report the synthesis of a cyclophellitol-derived β-l-arabinofuranosidase inhibitor, hypothesised to react with the catalytic nucleophile to form a non-hydrolysable adduct analogous to the mechanistic covalent intermediate. This β-l-arabinofuranosidase inhibitor reacts exclusively with the proposed cysteine thiol catalytic nucleophiles of representatives of GH families 127 and 146. X-ray crystal structures determined for the resulting adducts enable MD and QM/MM simulations, which provide insight into the mechanism of thioglycosyl enzyme intermediate breakdown. Leveraging the unique chemistry of cyclophellitol derivatives, the structures and simulations presented here support the assignment of a zinc-coordinated cysteine as the catalytic nucleophile and illuminate the finely tuned energetics of this remarkable metalloenzyme clan.
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http://dx.doi.org/10.1002/anie.202013920DOI Listing
March 2021

Structure of a GH51 α-L-arabinofuranosidase from Meripilus giganteus: conserved substrate recognition from bacteria to fungi.

Acta Crystallogr D Struct Biol 2020 Nov 16;76(Pt 11):1124-1133. Epub 2020 Oct 16.

York Structural Biology Laboratory, University of York, Heslington, York YO10 5DD, United Kingdom.

α-L-Arabinofuranosidases from glycoside hydrolase family 51 use a stereochemically retaining hydrolytic mechanism to liberate nonreducing terminal α-L-arabinofuranose residues from plant polysaccharides such as arabinoxylan and arabinan. To date, more than ten fungal GH51 α-L-arabinofuranosidases have been functionally characterized, yet no structure of a fungal GH51 enzyme has been solved. In contrast, seven bacterial GH51 enzyme structures, with low sequence similarity to the fungal GH51 enzymes, have been determined. Here, the crystallization and structural characterization of MgGH51, an industrially relevant GH51 α-L-arabinofuranosidase cloned from Meripilus giganteus, are reported. Three crystal forms were grown in different crystallization conditions. The unliganded structure was solved using sulfur SAD data collected from a single crystal using the I23 in vacuo diffraction beamline at Diamond Light Source. Crystal soaks with arabinose, 1,4-dideoxy-1,4-imino-L-arabinitol and two cyclophellitol-derived arabinose mimics reveal a conserved catalytic site and conformational itinerary between fungal and bacterial GH51 α-L-arabinofuranosidases.
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http://dx.doi.org/10.1107/S205979832001253XDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7604909PMC
November 2020

Rational Design of Mechanism-Based Inhibitors and Activity-Based Probes for the Identification of Retaining α-l-Arabinofuranosidases.

J Am Chem Soc 2020 03 26;142(10):4648-4662. Epub 2020 Feb 26.

York Structural Biology Laboratory, Department of Chemistry, The University of York, Heslington, York YO10 5DD, U.K.

Identifying and characterizing the enzymes responsible for an observed activity within a complex eukaryotic catabolic system remains one of the most significant challenges in the study of biomass-degrading systems. The debranching of both complex hemicellulosic and pectinaceous polysaccharides requires the production of α-l-arabinofuranosidases among a wide variety of coexpressed carbohydrate-active enzymes. To selectively detect and identify α-l-arabinofuranosidases produced by fungi grown on complex biomass, potential covalent inhibitors and probes which mimic α-l-arabinofuranosides were sought. The conformational free energy landscapes of free α-l-arabinofuranose and several rationally designed covalent α-l-arabinofuranosidase inhibitors were analyzed. A synthetic route to these inhibitors was subsequently developed based on a key Wittig-Still rearrangement. Through a combination of kinetic measurements, intact mass spectrometry, and structural experiments, the designed inhibitors were shown to efficiently label the catalytic nucleophiles of retaining GH51 and GH54 α-l-arabinofuranosidases. Activity-based probes elaborated from an inhibitor with an aziridine warhead were applied to the identification and characterization of α-l-arabinofuranosidases within the secretome of grown on arabinan. This method was extended to the detection and identification of α-l-arabinofuranosidases produced by eight biomass-degrading basidiomycete fungi grown on complex biomass. The broad applicability of the cyclophellitol-derived activity-based probes and inhibitors presented here make them a valuable new tool in the characterization of complex eukaryotic carbohydrate-degrading systems and in the high-throughput discovery of α-l-arabinofuranosidases.
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http://dx.doi.org/10.1021/jacs.9b11351DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7068720PMC
March 2020

Dynamic and Functional Profiling of Xylan-Degrading Enzymes in Secretomes Using Activity-Based Probes.

ACS Cent Sci 2019 Jun 24;5(6):1067-1078. Epub 2019 May 24.

Leiden Institute of Chemistry, Leiden University, Einsteinweg 55, 2300 RA Leiden, The Netherlands.

Plant polysaccharides represent a virtually unlimited feedstock for the generation of biofuels and other commodities. However, the extraordinary recalcitrance of plant polysaccharides toward breakdown necessitates a continued search for enzymes that degrade these materials efficiently under defined conditions. Activity-based protein profiling provides a route for the functional discovery of such enzymes in complex mixtures and under industrially relevant conditions. Here, we show the detection and identification of β-xylosidases and -β-1,4-xylanases in the secretomes of , by the use of chemical probes inspired by the β-glucosidase inhibitor cyclophellitol. Furthermore, we demonstrate the use of these activity-based probes (ABPs) to assess enzyme-substrate specificities, thermal stabilities, and other biotechnologically relevant parameters. Our experiments highlight the utility of ABPs as promising tools for the discovery of relevant enzymes useful for biomass breakdown.
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http://dx.doi.org/10.1021/acscentsci.9b00221DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6598175PMC
June 2019