1
|
Borg AJE, Esquivias O, Coines J, Rovira C, Nidetzky B. Enzymatische C4-Epimerisierung von UDP-Glucuronsäure: präzise gesteuerte Rotation eines transienten 4-Ketointermediats für eine invertierende Reaktion ohne Decarboxylierung. ANGEWANDTE CHEMIE (WEINHEIM AN DER BERGSTRASSE, GERMANY) 2023; 135:e202211937. [PMID: 38515538 PMCID: PMC10952283 DOI: 10.1002/ange.202211937] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 08/12/2022] [Indexed: 03/23/2024]
Abstract
AbstractUDP‐Glucuronsäure(UDP‐GlcA)‐4‐Epimerase repräsentiert eine wichtige Fragestellung in der Enzymkatalyse: die Balance zwischen konformativer Flexibilität und genauer Positionierung. Das Enzym koordiniert die C4‐Oxidation des Substrats durch NAD+ mit der Rotation eines leicht decarboxylierbaren β‐Ketosäure‐Intermediats im aktiven Zentrum zur Ermöglichung der stereoinvertierenden Reduktion der Ketogruppe durch NADH. Wir zeigen hier die nur schwer erfassbare Rotationskoordinate des 4‐Ketointermediats. Distorsion des Zuckerrings in eine Boot‐Konformation erzeugt torsionale Mobilität in der Bindungstasche des Enzyms. Die Endpunkte der Rotation zeigen den 4‐Ketozucker in einer unverformten 4C1‐Sesselkonformation. Die äquatorial positionierte Carboxylatgruppe ist ungünstig für die 4‐Ketozucker‐Decarboxylierung. Varianten der Epimerase zeigen Decarboxylierung, wenn sie die Bindung mit der Carboxylatgruppe im entgegengesetzten Rotationsisomer des Substrats entfernen. R185A/D‐Substitutionen wandeln die Epimerase in UDP‐Xylose‐Synthasen um, welche UDP‐GlcA in stereospezifischen, konfigurationserhaltenden Reaktionen decarboxylieren.
Collapse
Affiliation(s)
- Annika J. E. Borg
- Institut für Biotechnologie und BioprozesstechnikTechnische Universität GrazPetersgasse 12/18010GrazÖsterreich
| | - Oriol Esquivias
- Department of Inorganic and Organic Chemistry (Section of Organic Chemistry)Institute of Computational and Theoretical Chemistry (IQTCUB)Martí i Franquès 108028BarcelonaSpanien
| | - Joan Coines
- Department of Inorganic and Organic Chemistry (Section of Organic Chemistry)Institute of Computational and Theoretical Chemistry (IQTCUB)Martí i Franquès 108028BarcelonaSpanien
- Derzeitige Adresse: Nostrum BiodiscoveryAv. De Josep Tarradellas, 8–1008029BarcelonaSpanien
| | - Carme Rovira
- Department of Inorganic and Organic Chemistry (Section of Organic Chemistry)Institute of Computational and Theoretical Chemistry (IQTCUB)Martí i Franquès 108028BarcelonaSpanien
- Institució Catalana de Recerca i Estudis Avançats (ICREA)Passeig Lluís Companys, 2308010BarcelonaSpanien
| | - Bernd Nidetzky
- Institut für Biotechnologie und BioprozesstechnikTechnische Universität GrazPetersgasse 12/18010GrazÖsterreich
- Austrian Center of Industrial Biotechnology (acib)Krenngasse 378010GrazÖsterreich
| |
Collapse
|
2
|
Borg AJE, Esquivias O, Coines J, Rovira C, Nidetzky B. Enzymatic C4-Epimerization of UDP-Glucuronic Acid: Precisely Steered Rotation of a Transient 4-Keto Intermediate for an Inverted Reaction without Decarboxylation. Angew Chem Int Ed Engl 2023; 62:e202211937. [PMID: 36308301 PMCID: PMC10107529 DOI: 10.1002/anie.202211937] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/12/2022] [Revised: 10/03/2022] [Accepted: 10/26/2022] [Indexed: 11/06/2022]
Abstract
UDP-glucuronic acid (UDP-GlcA) 4-epimerase illustrates an important problem regarding enzyme catalysis: balancing conformational flexibility with precise positioning. The enzyme coordinates the C4-oxidation of the substrate by NAD+ and rotation of a decarboxylation-prone β-keto acid intermediate in the active site, enabling stereoinverting reduction of the keto group by NADH. We reveal the elusive rotational landscape of the 4-keto intermediate. Distortion of the sugar ring into boat conformations induces torsional mobility in the enzyme's binding pocket. The rotational endpoints show that the 4-keto sugar has an undistorted 4 C1 chair conformation. The equatorially placed carboxylate group disfavors decarboxylation of the 4-keto sugar. Epimerase variants lead to decarboxylation upon removal of the binding interactions with the carboxylate group in the opposite rotational isomer of the substrate. Substitutions R185A/D convert the epimerase into UDP-xylose synthases that decarboxylate UDP-GlcA in stereospecific, configuration-retaining reactions.
Collapse
Affiliation(s)
- Annika J E Borg
- Institute of Biotechnology and Biochemical Engineering, Graz University of Technology, Petersgasse 12/1, 8010, Graz, Austria
| | - Oriol Esquivias
- Department of Inorganic and Organic Chemistry (Section of Organic Chemistry), Institute of Computational and Theoretical Chemistry (IQTCUB), Martí i Franquès 1, 08028, Barcelona, Spain
| | - Joan Coines
- Department of Inorganic and Organic Chemistry (Section of Organic Chemistry), Institute of Computational and Theoretical Chemistry (IQTCUB), Martí i Franquès 1, 08028, Barcelona, Spain.,Present address: Nostrum Biodiscovery, Av. De Josep Tarradellas, 8-10, 08029, Barcelona, Spain
| | - Carme Rovira
- Department of Inorganic and Organic Chemistry (Section of Organic Chemistry), Institute of Computational and Theoretical Chemistry (IQTCUB), Martí i Franquès 1, 08028, Barcelona, Spain.,Institució Catalana de Recerca i Estudis Avançats (ICREA), Passeig Lluís Companys, 23, 08010, Barcelona, Spain
| | - Bernd Nidetzky
- Institute of Biotechnology and Biochemical Engineering, Graz University of Technology, Petersgasse 12/1, 8010, Graz, Austria.,Austrian Center of Industrial Biotechnology (acib), Krenngasse 37, 8010, Graz, Austria
| |
Collapse
|
3
|
Rapp C, Nidetzky B. Hydride Transfer Mechanism of Enzymatic Sugar Nucleotide C2 Epimerization Probed with a Loose-Fit CDP-Glucose Substrate. ACS Catal 2022; 12:6816-6830. [PMID: 35747200 PMCID: PMC9207888 DOI: 10.1021/acscatal.2c00257] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/14/2022] [Revised: 05/12/2022] [Indexed: 11/29/2022]
Abstract
![]()
Transient oxidation–reduction
through hydride transfer with
tightly bound NAD coenzyme is used by a large class of sugar nucleotide
epimerases to promote configurational inversion of carbon stereocenters
in carbohydrate substrates. A requirement for the epimerases to coordinate
hydride abstraction and re-addition with substrate rotation in the
binding pocket poses a challenge for dynamical protein conformational
selection linked to enzyme catalysis. Here, we studied the thermophilic
C2 epimerase from Thermodesulfatator atlanticus (TaCPa2E) in combination with a slow CDP-glucose
substrate (kcat ≈ 1.0 min–1; 60 °C) to explore the sensitivity of the enzymatic hydride
transfer toward environmental fluctuations affected by temperature
(20–80 °C). We determined noncompetitive primary kinetic
isotope effects (KIE) due to 2H at the glucose C2 and showed
that a normal KIE on the kcat (Dkcat) reflects isotope sensitivity of
the hydrogen abstraction to enzyme-NAD+ in a rate-limiting
transient oxidation. The Dkcat peaked at 40 °C was 6.1 and decreased to 2.1 at low (20 °C)
and 3.3 at high temperature (80 °C). The temperature profiles
for kcat with the 1H and 2H substrate showed a decrease in the rate below a dynamically
important breakpoint (∼40 °C), suggesting an equilibrium
shift to an impaired conformational landscape relevant for catalysis
in the low-temperature region. Full Marcus-like model fits of the
rate and KIE profiles provided evidence for a high-temperature reaction
via low-frequency conformational sampling associated with a broad
distribution of hydride donor–acceptor distances (long-distance
population centered at 3.31 ± 0.02 Å), only poorly suitable
for quantum mechanical tunneling. Collectively, dynamical characteristics
of TaCPa2E-catalyzed hydride transfer during transient
oxidation of CDP-glucose reveal important analogies to mechanistically
simpler enzymes such as alcohol dehydrogenase and dihydrofolate reductase.
A loose-fit substrate (in TaCPa2E) resembles structural
variants of these enzymes by extensive dynamical sampling to balance
conformational flexibility and catalytic efficiency.
Collapse
Affiliation(s)
- Christian Rapp
- Institute of Biotechnology and Biochemical Engineering, Graz University of Technology, Petersgasse 10-12/1, 8010 Graz, Austria
| | - Bernd Nidetzky
- Institute of Biotechnology and Biochemical Engineering, Graz University of Technology, Petersgasse 10-12/1, 8010 Graz, Austria
- Austrian Centre of Industrial Biotechnology (ACIB), Petersgasse 14, 8010 Graz, Austria
| |
Collapse
|
4
|
Wang Y, Li X, Wei J, Zhang X, Liu Y. Mechanism of Sugar Ring Contraction and Closure Catalyzed by UDP-d-apiose/UDP-d-xylose Synthase (UAXS). J Chem Inf Model 2022; 62:632-646. [PMID: 35043627 DOI: 10.1021/acs.jcim.1c01408] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Uridine diphosphate (UDP)-apiose/UDP-xylose synthase (UAXS) is a member of the short-chain dehydrogenase/reductase superfamily (SDR), which catalyzes the ring contraction and closure of UDP-d-glucuronic acid (UDP-GlcA), affording UDP-apiose and UDP-xylose. UAXS is a special enzyme that integrates ring-opening, decarboxylation, rearrangement, and ring closure/contraction in a single active site. Recently, the ternary complex structure of UAXS was crystallized from Arabidopsis thaliana. In this work, to gain insights into the detailed formation mechanism of UDP-apiose and UDP-xylose, an enzyme-substrate reactant model has been constructed and quantum mechanical/molecular mechanical (QM/MM) calculations have been performed. Our calculation results reveal that the reaction starts from the C4-OH oxidation, which is accompanied by the conformational transformation of the sugar ring from chair type to boat type. The sugar ring-opening is prior to decarboxylation, and the deprotonation of the C2-OH group is the prerequisite for sugar ring-opening. Moreover, the keto-enol tautomerization of the decarboxylated intermediate is a necessary step for ring closure/contraction. Based on our calculation results, more UDP-apiose product was expected, which is in line with the experimental observation. Three titratable residues, Tyr185, Cys100, and Cys140, steer the reaction by proton transfer from or to UDP-GlcA, and Arg182, Glu141, and D337 constitute a proton conduit for sugar C2-OH deprotonation. Although Thr139 and Tyr105 are not directly involved in the enzymatic reaction, they are responsible for promoting the catalysis by forming hydrogen-bonding interactions with GlcA. Our calculations may provide useful information for understanding the catalysis of the SDR family.
Collapse
Affiliation(s)
- Yijing Wang
- School of Chemistry and Chemical Engineering, Shandong University, Jinan, Shandong 250100, China
| | - Xinyi Li
- School of Chemistry and Chemical Engineering, Shandong University, Jinan, Shandong 250100, China
| | - Jingjing Wei
- School of Chemistry and Chemical Engineering, Shandong University, Jinan, Shandong 250100, China
| | - Xue Zhang
- School of Chemistry and Chemical Engineering, Shandong University, Jinan, Shandong 250100, China
| | - Yongjun Liu
- School of Chemistry and Chemical Engineering, Shandong University, Jinan, Shandong 250100, China
| |
Collapse
|
5
|
Fushinobu S. Molecular evolution and functional divergence of UDP-hexose 4-epimerases. Curr Opin Chem Biol 2020; 61:53-62. [PMID: 33171387 DOI: 10.1016/j.cbpa.2020.09.007] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/26/2020] [Revised: 09/23/2020] [Accepted: 09/25/2020] [Indexed: 01/08/2023]
Abstract
UDP-glucose 4-epimerase (GalE) catalyzes the interconversion of UDP-glucose (UDP-Glc) and UDP-galactose (UDP-Gal) and/or the interconversion of UDP-N-acetylglucosamine (UDP-GlcNAc) and UDP-N-acetylgalactosamine (UDP-GalNAc) in sugar metabolism. GalEs belong to the short-chain dehydrogenase/reductase superfamily, use a conserved 'transient keto intermediate' mechanism and have variable substrate specificity. GalEs have been classified into three groups based on substrate specificity: group 1 prefers UDP-Glc/Gal, group 3 prefers UDP-GlcNAc/GalNAc, and group 2 has comparable activities for both types of the substrates. The phylogenetic relationship and structural basis for the specificities of GalEs revealed possible molecular evolution of UDP-hexose 4-epimerases in various organisms. Based on the recent advances in studies on GalEs and related enzymes, an updated view of their evolutional diversification is presented.
Collapse
Affiliation(s)
- Shinya Fushinobu
- Department of Biotechnology, The University of Tokyo, Tokyo, 113-8657, Japan; Collaborative Research Institute for Innovative Microbiology, The University of Tokyo, Tokyo, 113-8657, Japan.
| |
Collapse
|
6
|
Borg AJE, Beerens K, Pfeiffer M, Desmet T, Nidetzky B. Stereo-electronic control of reaction selectivity in short-chain dehydrogenases: Decarboxylation, epimerization, and dehydration. Curr Opin Chem Biol 2020; 61:43-52. [PMID: 33166830 DOI: 10.1016/j.cbpa.2020.09.010] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/15/2020] [Revised: 09/18/2020] [Accepted: 09/27/2020] [Indexed: 12/20/2022]
Abstract
Sugar nucleotide-modifying enzymes of the short-chain dehydrogenase/reductase type use transient oxidation-reduction by a tightly bound nicotinamide cofactor as a common strategy of catalysis to promote a diverse set of reactions, including decarboxylation, single- or double-site epimerization, and dehydration. Although the basic mechanistic principles have been worked out decades ago, the finely tuned control of reactivity and selectivity in several of these enzymes remains enigmatic. Recent evidence on uridine 5'-diphosphate (UDP)-glucuronic acid decarboxylases (UDP-xylose synthase, UDP-apiose/UDP-xylose synthase) and UDP-glucuronic acid-4-epimerase suggests that stereo-electronic constraints established at the enzyme's active site control the selectivity, and the timing of the catalytic reaction steps, in the conversion of the common substrate toward different products. The mechanistic idea of stereo-electronic control is extended to epimerases and dehydratases that deprotonate the Cα of the transient keto-hexose intermediate. The human guanosine 5'-diphosphate (GDP)-mannose 4,6-dehydratase was recently shown to use a minimal catalytic machinery, exactly as predicted earlier from theoretical considerations, for the β-elimination of water from the keto-hexose species.
Collapse
Affiliation(s)
- Annika J E Borg
- Institute of Biotechnology and Biochemical Engineering, Graz University of Technology, NAWI Graz, 8010, Graz, Austria
| | - Koen Beerens
- Centre for Synthetic Biology, Department of Biotechnology, Ghent University, 9000, Ghent, Belgium
| | - Martin Pfeiffer
- Institute of Biotechnology and Biochemical Engineering, Graz University of Technology, NAWI Graz, 8010, Graz, Austria; Austrian Centre of Industrial Biotechnology (acib), 8010, Graz, Austria
| | - Tom Desmet
- Centre for Synthetic Biology, Department of Biotechnology, Ghent University, 9000, Ghent, Belgium; Austrian Centre of Industrial Biotechnology (acib), 8010, Graz, Austria
| | - Bernd Nidetzky
- Institute of Biotechnology and Biochemical Engineering, Graz University of Technology, NAWI Graz, 8010, Graz, Austria; Austrian Centre of Industrial Biotechnology (acib), 8010, Graz, Austria.
| |
Collapse
|
7
|
Borg AJE, Dennig A, Weber H, Nidetzky B. Mechanistic characterization of UDP-glucuronic acid 4-epimerase. FEBS J 2020; 288:1163-1178. [PMID: 32645249 PMCID: PMC7984243 DOI: 10.1111/febs.15478] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/06/2020] [Revised: 06/22/2020] [Accepted: 07/06/2020] [Indexed: 12/27/2022]
Abstract
UDP-glucuronic acid (UDP-GlcA) is a central precursor in sugar nucleotide biosynthesis and common substrate for C4-epimerases and decarboxylases releasing UDP-galacturonic acid (UDP-GalA) and UDP-pentose products, respectively. Despite the different reactions catalyzed, the enzymes are believed to share mechanistic analogy rooted in their joint membership to the short-chain dehydrogenase/reductase (SDR) protein superfamily: Oxidation at the substrate C4 by enzyme-bound NAD+ initiates the catalytic pathway. Here, we present mechanistic characterization of the C4-epimerization of UDP-GlcA, which in comparison with the corresponding decarboxylation has been largely unexplored. The UDP-GlcA 4-epimerase from Bacillus cereus functions as a homodimer and contains one NAD+ /subunit (kcat = 0.25 ± 0.01 s-1 ). The epimerization of UDP-GlcA proceeds via hydride transfer from and to the substrate's C4 while retaining the enzyme-bound cofactor in its oxidized form (≥ 97%) at steady state and without trace of decarboxylation. The kcat for UDP-GlcA conversion shows a kinetic isotope effect of 2.0 (±0.1) derived from substrate deuteration at C4. The proposed enzymatic mechanism involves a transient UDP-4-keto-hexose-uronic acid intermediate whose formation is rate-limiting overall, and is governed by a conformational step before hydride abstraction from UDP-GlcA. Precise positioning of the substrate in a kinetically slow binding step may be important for the epimerase to establish stereo-electronic constraints in which decarboxylation of the labile β-keto acid species is prevented effectively. Mutagenesis and pH studies implicate the conserved Tyr149 as the catalytic base for substrate oxidation and show its involvement in the substrate positioning step. Collectively, this study suggests that based on overall mechanistic analogy, stereo-electronic control may be a distinguishing feature of catalysis by SDR-type epimerases and decarboxylases active on UDP-GlcA.
Collapse
Affiliation(s)
- Annika J E Borg
- Institute of Biotechnology and Biochemical Engineering, Graz University of Technology, NAWI Graz, Austria
| | - Alexander Dennig
- Institute of Biotechnology and Biochemical Engineering, Graz University of Technology, NAWI Graz, Austria.,Austrian Centre of Industrial Biotechnology, Graz, Austria
| | - Hansjörg Weber
- Institute of Organic Chemistry, Graz University of Technology, NAWI Graz, Austria
| | - Bernd Nidetzky
- Institute of Biotechnology and Biochemical Engineering, Graz University of Technology, NAWI Graz, Austria.,Austrian Centre of Industrial Biotechnology, Graz, Austria
| |
Collapse
|
8
|
Iacovino LG, Savino S, Borg AJE, Binda C, Nidetzky B, Mattevi A. Crystallographic snapshots of UDP-glucuronic acid 4-epimerase ligand binding, rotation, and reduction. J Biol Chem 2020; 295:12461-12473. [PMID: 32661196 DOI: 10.1074/jbc.ra120.014692] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/08/2020] [Revised: 07/10/2020] [Indexed: 11/06/2022] Open
Abstract
UDP-glucuronic acid is converted to UDP-galacturonic acid en route to a variety of sugar-containing metabolites. This reaction is performed by a NAD+-dependent epimerase belonging to the short-chain dehydrogenase/reductase family. We present several high-resolution crystal structures of the UDP-glucuronic acid epimerase from Bacillus cereus The geometry of the substrate-NAD+ interactions is finely arranged to promote hydride transfer. The exquisite complementarity between glucuronic acid and its binding site is highlighted by the observation that the unligated cavity is occupied by a cluster of ordered waters whose positions overlap the polar groups of the sugar substrate. Co-crystallization experiments led to a structure where substrate- and product-bound enzymes coexist within the same crystal. This equilibrium structure reveals the basis for a "swing and flip" rotation of the pro-chiral 4-keto-hexose-uronic acid intermediate that results from glucuronic acid oxidation, placing the C4' atom in position for receiving a hydride ion on the opposite side of the sugar ring. The product-bound active site is almost identical to that of the substrate-bound structure and satisfies all hydrogen-bonding requirements of the ligand. The structure of the apoenzyme together with the kinetic isotope effect and mutagenesis experiments further outlines a few flexible loops that exist in discrete conformations, imparting structural malleability required for ligand rotation while avoiding leakage of the catalytic intermediate and/or side reactions. These data highlight the double nature of the enzymatic mechanism: the active site features a high degree of precision in substrate recognition combined with the flexibility required for intermediate rotation.
Collapse
Affiliation(s)
- Luca Giacinto Iacovino
- Department of Biology and Biotechnology "Lazzaro Spallanzani", University of Pavia, Pavia, Italy
| | - Simone Savino
- Institute of Biotechnology and Biochemical Engineering, Graz University of Technology, NAWI Graz, Graz, Austria
| | - Annika J E Borg
- Institute of Biotechnology and Biochemical Engineering, Graz University of Technology, NAWI Graz, Graz, Austria
| | - Claudia Binda
- Department of Biology and Biotechnology "Lazzaro Spallanzani", University of Pavia, Pavia, Italy
| | - Bernd Nidetzky
- Institute of Biotechnology and Biochemical Engineering, Graz University of Technology, NAWI Graz, Graz, Austria .,Austrian Centre of Industrial Biotechnology, Graz, Austria
| | - Andrea Mattevi
- Department of Biology and Biotechnology "Lazzaro Spallanzani", University of Pavia, Pavia, Italy
| |
Collapse
|
9
|
Savino S, Borg AJE, Dennig A, Pfeiffer M, de Giorgi F, Weber H, Dubey KD, Rovira C, Mattevi A, Nidetzky B. Deciphering the enzymatic mechanism of sugar ring contraction in UDP-apiose biosynthesis. Nat Catal 2019; 2:1115-1123. [PMID: 31844840 PMCID: PMC6914363 DOI: 10.1038/s41929-019-0382-8] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022]
Abstract
D-Apiose is a C-branched pentose sugar important for plant cell wall development. Its biosynthesis as UDP-D-apiose involves decarboxylation of the UDP-D-glucuronic acid precursor coupled to pyranosyl-to-furanosyl sugar ring contraction. This unusual multistep reaction is catalyzed within a single active site by UDP-D-apiose/UDP-D-xylose synthase (UAXS). Here, we decipher the UAXS catalytic mechanism based on crystal structures of the enzyme from Arabidopsis thaliana, molecular dynamics simulations expanded by QM/MM calculations, and mutational-mechanistic analyses. Our studies show how UAXS uniquely integrates a classical catalytic cycle of oxidation and reduction by a tightly bound nicotinamide coenzyme with retro-aldol/aldol chemistry for the sugar ring contraction. They further demonstrate that decarboxylation occurs only after the sugar ring opening and identify the thiol group of Cys100 in steering the sugar skeleton rearrangement by proton transfer to and from the C3’. The mechanistic features of UAXS highlight the evolutionary expansion of the basic catalytic apparatus of short-chain dehydrogenases/reductases for functional versatility in sugar biosynthesis.
Collapse
Affiliation(s)
- Simone Savino
- Department of Biology and Biotechnology, University of Pavia, Via Ferrata 1, 27100, Pavia, Italy.,Austrian Centre of Industrial Biotechnology, Petersgasse 14, 8010 Graz, Austria
| | - Annika J E Borg
- Institute of Biotechnology and Biochemical Engineering, Graz University of Technology, NAWI Graz, Petersgasse 12, 8010 Graz, Austria
| | - Alexander Dennig
- Austrian Centre of Industrial Biotechnology, Petersgasse 14, 8010 Graz, Austria.,Institute of Biotechnology and Biochemical Engineering, Graz University of Technology, NAWI Graz, Petersgasse 12, 8010 Graz, Austria
| | - Martin Pfeiffer
- Institute of Biotechnology and Biochemical Engineering, Graz University of Technology, NAWI Graz, Petersgasse 12, 8010 Graz, Austria
| | - Francesca de Giorgi
- Department of Biology and Biotechnology, University of Pavia, Via Ferrata 1, 27100, Pavia, Italy.,Institute of Biotechnology and Biochemical Engineering, Graz University of Technology, NAWI Graz, Petersgasse 12, 8010 Graz, Austria
| | - Hansjörg Weber
- Institute of Organic Chemistry, Graz University of Technology, NAWI Graz, Stremayrgasse 9, 8010 Graz, Austria
| | - Kshatresh Dutta Dubey
- Department of Inorganic and Organic Chemistry (Organic Chemistry Section) & Institute of Computational and Theoretical Chemistry (IQTCUB), University of Barcelona, Martí i Franquès 1, 08028 Barcelona, Spain
| | - Carme Rovira
- Department of Inorganic and Organic Chemistry (Organic Chemistry Section) & Institute of Computational and Theoretical Chemistry (IQTCUB), University of Barcelona, Martí i Franquès 1, 08028 Barcelona, Spain.,Catalan Institution for Advanced Studies (ICREA), Passeig Lluís Companys 23, 08010 Barcelona
| | - Andrea Mattevi
- Department of Biology and Biotechnology, University of Pavia, Via Ferrata 1, 27100, Pavia, Italy
| | - Bernd Nidetzky
- Austrian Centre of Industrial Biotechnology, Petersgasse 14, 8010 Graz, Austria.,Institute of Biotechnology and Biochemical Engineering, Graz University of Technology, NAWI Graz, Petersgasse 12, 8010 Graz, Austria
| |
Collapse
|
10
|
Tuckey RC, Tang EKY, Maresse SR, Delaney DS. Catalytic properties of 25-hydroxyvitamin D3 3-epimerase in rat and human liver microsomes. Arch Biochem Biophys 2019; 666:16-21. [PMID: 30926433 DOI: 10.1016/j.abb.2019.03.010] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/03/2018] [Revised: 02/26/2019] [Accepted: 03/25/2019] [Indexed: 10/27/2022]
Abstract
25-Hydroxyvitamin D3 3-epimerase catalyzes the 3β → 3α epimerization of 25-hydroxyvitamin D3 (25(OH)D3) producing 3-epi-25-hydroxyvitamin D3 (3-epi-25(OH)D3). 3-Epi-25(OH)D3 is one of the most abundant forms of vitamin D present in the serum. It can be converted to 3-epi-1α,25-dihydroxyvitamin D3 by CYP27B1 which generally displays lower biological activity than 1α,25-dihydroxyvitamin D3 (1,25(OH)2D3). The 25(OH)D3 3-epimerase has been poorly characterized to date and the gene encoding it has not been identified. The 3-epimerase has been reported to be present in the microsomal fraction of cells, including liver cells, and to use NADPH as cofactor. It can also act on 1,25(OH)2D3 and 24,25(OH)2D3 forming the 3α-epimers. In this study we have characterized the activity of the 25(OH)D3 3-epimerase in rat and human liver microsomes, using 25(OH)D3 as substrate and HPLC to analyze product formation. For both rat and human liver microsomes the preferred cofactor was NADH, with the rat enzyme displaying a 6-fold greater catalytic efficiency (Vmax/Km) for NADH over that for NADPH. No activity was observed with oxidized cofactor, either NAD+ or NADP+. This was unexpected since the initial step in the epimerization, predicted to be the oxidation of the 3β-OH to a ketone, would require oxidized cofactor. The rat 3-epimerase in microsomes gave a Km for 25(OH)D3 of 14 μM. The reverse reaction, conversion of 3-epi-25(OH)D3 to 25(OH)D3, was catalyzed by both rat and human liver microsomes but at lower rates than the forward reaction. In conclusion, both rat and human 25-hydroxyvitamin D3 3-epimerase catalyze the reversible interconversion of 25(OH)D3 and 3-epi-25(OH)D3, and use NADH as the preferred cofactor. The lack of requirement for exogenous NAD+ suggests that the enzyme has a tightly bound NAD+ in its active site that is released only upon its reduction.
Collapse
Affiliation(s)
- Robert C Tuckey
- School of Molecular Sciences, The University of Western Australia, Perth, WA, 6009, Australia.
| | - Edith K Y Tang
- School of Molecular Sciences, The University of Western Australia, Perth, WA, 6009, Australia
| | - Stephanie R Maresse
- School of Molecular Sciences, The University of Western Australia, Perth, WA, 6009, Australia
| | - Derek S Delaney
- School of Molecular Sciences, The University of Western Australia, Perth, WA, 6009, Australia
| |
Collapse
|
11
|
Beerens K, Soetaert W, Desmet T. UDP-hexose 4-epimerases: a view on structure, mechanism and substrate specificity. Carbohydr Res 2015; 414:8-14. [PMID: 26162744 DOI: 10.1016/j.carres.2015.06.006] [Citation(s) in RCA: 43] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/02/2015] [Revised: 06/09/2015] [Accepted: 06/13/2015] [Indexed: 12/19/2022]
Abstract
UDP-sugar 4-epimerase (GalE) belongs to the short-chain dehydrogenase/reductase (SDR) superfamily of proteins and is one of enzymes in the Leloir pathway. They have been shown to be important virulence factors in a number of Gram-negative pathogens and to be involved in the biosynthesis of different polysaccharide structures. The metabolic disease type III galactosemia is caused by detrimental mutations in the human GalE. GalE and related enzymes display unusual enzymologic, chemical, and stereochemical properties; including irreversible binding of the cofactor NAD and uridine nucleotide-induced activation of this cofactor. These epimerases have been found active on UDP-hexoses, the N-acetylated and uronic acid forms thereof as well as UDP-pentoses. As they are involved in different pathways and functions, a deeper understanding of the enzymes, and their substrate promiscuity and/or selectivity, could lead to drug and vaccine design as well as antibiotic and probiotic development. This review summarizes the research performed on UDP-sugar 4-epimerases' structure, mechanism and substrate promiscuity.
Collapse
Affiliation(s)
- Koen Beerens
- Centre for Industrial Biotechnology and Biocatalysis, Faculty of Bioscience Engineering, Ghent University, Coupure links 653, 9000 Gent, Belgium.
| | - Wim Soetaert
- Centre for Industrial Biotechnology and Biocatalysis, Faculty of Bioscience Engineering, Ghent University, Coupure links 653, 9000 Gent, Belgium
| | - Tom Desmet
- Centre for Industrial Biotechnology and Biocatalysis, Faculty of Bioscience Engineering, Ghent University, Coupure links 653, 9000 Gent, Belgium
| |
Collapse
|
12
|
Frey PA, Hegeman AD. Chemical and stereochemical actions of UDP-galactose 4-epimerase. Acc Chem Res 2013; 46:1417-26. [PMID: 23339688 DOI: 10.1021/ar300246k] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Uridine(5')diphospho(1)α-D-galactose (UDP-gal) provides all galactosyl units in biologically synthesized carbohydrates. All healthy cells produce UDP-gal from uridine(5')diphospho(1)α-D-glucose (UDP-glc) by the action of UDP-galactose 4-epimerase (GalE). This Account provides our recent results describing unusual mechanistic features of this enzyme. Fully active GalE is dimeric and contains one tightly bound nicotinamide adenine dinucleotide (NAD) per subunit. The NAD undergoes reversible reduction to NADH in the chemical mechanism. GalE displays unusual enzymological, chemical, and stereochemical properties. These include practically irreversible binding of NAD, nonstereospecific hydride transfer, uridine nucleotide-induced activation of NAD, Tyr149 as a base catalyst, and [GalE-NADH]-oxidation in one-electron steps by one-electron acceptors. Early studies revealed that uridine(5')diphospho(1)α-D-4-ketopyranose (UDP-4-ketopyranose) and NADH are reaction intermediates. Weak binding of the 4-ketopyranosyl moiety and strong binding of the UDP-moiety allowed either face of the 4-ketopyranosyl moiety to accept hydride from NADH. In crystal structures of GalE, NAD bound within a Rossmann-type fold and uridine nucleotides within a substrate domain. Structures of [GalE-NADH] in complex with UDP-glc show Lys153, Tyr149, and Ser124 in contact with NAD or glucosyl-C4(OH). Lys153 forms hydrogen bonds to the ribosyl-OH groups of NAD. The phenolate of Tyr149 is associated with both the nicotinamide ring of NAD and glucosyl-C4(OH). Ser124 is hydrogen-bonded to glucosyl-C4(OH). Spectrophotometry studies show a pH-dependent charge transfer (CT) complex between Tyr149 and NAD. The CT-complex has a pKa of 6.1, which results in bleaching of the CT-band. The CT-band also bleaches upon binding of a uridine nucleotide. Kinetic experiments with wild-type GalE and Ser124Ala-GalE show the same kinetic pKa values as the corresponding CT-band pKa, which point to Tyr149 as the base catalyst for hydride transfer. We used NMR studies to verify that uridine nucleotide binding polarizes nicotinamide π-electrons. The binding of uridine(5')-diphosphate (UDP) to GalE-[nicotinamide-1-¹⁵N]NAD shifts the ¹⁵N-signal upfield 3 ppm, whereas UDP-binding to GalE-[nicotinamide-4-¹³C]NAD shifts the ¹³C-signal downfield by 3.4 ppm. Electrochemical and ¹³C NMR data for a series of N-alkylnicotinamides show that the 3.4 ppm downfield ¹³C-perturbation in GalE corresponds to an elevation of the NAD reduction potential by 150 mV. These results account for the uridine nucleotide-dependence in the reduction of [GalE-NAD] by glucose or NaBH₃CN. Kinetics in the reduction of Tyr149Phe- and Lys153Met-GalE-NAD implicate Tyr149 and Lys153 in the nucleotide-dependent reduction of NAD. They further implicate electrostatic repulsion between N1 of NAD and the ε-aminium group of Lys153 in nucleotide-induced activation of NAD. In an O₂-dependent reaction, [GalE-NADH] reduces the stable radical UDP-TEMPO with production of superoxide radical. The reaction must proceed by way of a NAD-pyridinyl radical intermediate.
Collapse
Affiliation(s)
- Perry A. Frey
- Department of Biochemistry, University of Wisconsin—Madison, 1710 University Avenue, Madison, Wisconsin 53705, United States
| | - Adrian D. Hegeman
- Department of Biochemistry, University of Wisconsin—Madison, 1710 University Avenue, Madison, Wisconsin 53705, United States
| |
Collapse
|
13
|
Sims JW, Schmidt EW. Thioesterase-Like Role for Fungal PKS-NRPS Hybrid Reductive Domains. J Am Chem Soc 2008; 130:11149-55. [DOI: 10.1021/ja803078z] [Citation(s) in RCA: 91] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023]
Affiliation(s)
- James W. Sims
- Department of Medicinal Chemistry, University of Utah, 30 South 2000 East Rm 201, Salt Lake City, Utah, 84112
| | - Eric W. Schmidt
- Department of Medicinal Chemistry, University of Utah, 30 South 2000 East Rm 201, Salt Lake City, Utah, 84112
| |
Collapse
|
14
|
Chhay JS, Vargas CA, McCorvie TJ, Fridovich-Keil JL, Timson DJ. Analysis of UDP-galactose 4'-epimerase mutations associated with the intermediate form of type III galactosaemia. J Inherit Metab Dis 2008; 31:108-16. [PMID: 18188677 DOI: 10.1007/s10545-007-0790-9] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/10/2007] [Revised: 11/20/2007] [Accepted: 12/04/2007] [Indexed: 11/29/2022]
Abstract
Type III galactosaemia is a hereditary disease caused by reduced activity in the Leloir pathway enzyme, UDP-galactose 4'-epimerase (GALE). Traditionally, the condition has been divided into two forms-a mild, or peripheral, form and a severe, or generalized, form. Recently it has become apparent that there are disease states which are intermediate between these two extremes. Three mutations associated with this intermediate form (S81R, T150M and P293L) were analysed for their kinetic and structural properties in vitro and their effects on galactose-sensitivity of Saccharomyces cerevisiae cells that were deleted for the yeast GALE homologue Gal10p. All three mutations result in impairment of the kinetic parameters (principally the turnover number, k (cat)) compared with the wild-type enzyme. However, the degree of impairment was mild compared with that seen with the mutation (V94M) associated with the generalized form of epimerase deficiency galactosaemia. None of the three mutations tested affected the ability of the protein to dimerize in solution or its susceptibility to limited proteolysis in vitro. Finally, in the yeast model, each of the mutated patient alleles was able to complement the galactose-sensitivity of gal10Delta cells as fully as was the wild-type human allele. Furthermore, there was no difference from control in metabolite profile following galactose exposure for any of these strains. Thus we conclude that the subtle biochemical and metabolic abnormalities detected in patients expressing these GALE alleles likely reflect, at least in part, the reduced enzymatic activity of the encoded GALE proteins.
Collapse
Affiliation(s)
- J S Chhay
- Department of Human Genetics, Emory University School of Medicine, Emory University, Atlanta, Georgia, USA
| | | | | | | | | |
Collapse
|
15
|
Abstract
UDP-galactose 4-epimerase (GALE, EC 5.1.3.2) catalyses the interconversion of UDP-glucose and UDP-galactose. Point mutations in this enzyme are associated with the genetic disease, type III galactosemia, which exists in two forms - a milder, or peripheral, form and a more severe, or generalized, form. Recombinant wild-type GALE, and nine disease-causing mutations, have all been expressed in, and purified from, Escherichia coli in soluble, active forms. Two of the mutations (N34S and G319E) display essentially wild-type kinetics. The remainder (G90E, V94M, D103G, L183P, K257R, L313M and R335H) are all impaired in turnover number (k cat) and specificity constant (k cat/Km), with G90E and V94M (which is associated with the generalized form of galactosemia) being the most affected. None of the mutations results in a greater than threefold change in the Michaelis constant (Km). Protein-protein crosslinking suggests that none of the mutants are impaired in homodimer formation. The L183P mutation suffers from severe proteolytic degradation during expression and purification. N34S, G90E and D103G all show increased susceptibility to digestion in limited proteolysis experiments. Therefore, it is suggested that reduced catalytic efficiency and increased proteolytic susceptibility of GALE are causative factors in type III galactosemia. Furthermore, there is an approximate correlation between the severity of these defects in the protein structure and function, and the symptoms observed in patients.
Collapse
Affiliation(s)
- David J Timson
- School of Biology & Biochemistry, Queen's University Belfast, Medical Biology Centre, Belfast, UK.
| |
Collapse
|
16
|
Hwang CC, Chang YH, Hsu CN, Hsu HH, Li CW, Pon HI. Mechanistic Roles of Ser-114, Tyr-155, and Lys-159 in 3α-Hydroxysteroid Dehydrogenase/Carbonyl Reductase from Comamonas testosteroni. J Biol Chem 2005; 280:3522-8. [PMID: 15572373 DOI: 10.1074/jbc.m411751200] [Citation(s) in RCA: 34] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
3alpha-hydroxysteroid dehydrogenase/carbonyl reductase (3alpha-HSD/CR) from Comamonas testosteroni, a short chain dehydrogenase/reductase, catalyzes the oxidation of androsterone with NAD+ to form androstanedione and NADH. A catalytic triad of Ser-114, Tyr-155, and Lys-159 in 3alpha-HSD/CR has been proposed based on structural analysis and sequence alignment of the short chain dehydrogenase/reductase family. The 3alpha-HSD/CR-catalyzed reaction has not been kinetically analyzed in detail, however. In this study, we combined steady-state kinetics, site-directed mutagenesis, and pH profile to explore the function of Ser-114, Tyr-155, and Lys-159 in 3alpha-HSD/CR-catalyzed reaction. The catalytic efficiency of wild-type and mutants S114A, Y155F, K159A, and Y155F/K159A is 4.3 x 10(7), 7.3 x 10(4), 1.7 x 10(4), 2.4 x 10(5), and 71 m(-1)s(-1), respectively. The values of pKa on kcat/Km for the wild-type, S114A, Y155F, K159A, and Y155F/K159A are 7.2, 7.4, 8.4, 9.1, and 10.2, respectively. Mutant S114A/Y155F exhibits a pH-independent profile with 10(-5) times of wild-type activity at pH 10.5. The activity decreases as the pH lowers, which indicates that a functional group with an apparent pKa of 7.2 is involved in the general base catalysis for wild-type 3alpha-HSD/CR. The pKa shift to 9.1 for mutant K159A suggests the role of Lys-159 is to lower the pKa of the residues involved in the general base catalysis. Because pH dependence is observed for both S114A and Y155F mutants and pH independence is observed in S114A/Y155F, Tyr-155 may be important as a general base catalysis in the wild-type, whereas Ser-114 may act as a general base on mutant Y155F to catalyze the reaction.
Collapse
Affiliation(s)
- Chi-Ching Hwang
- Department of Biochemistry, Kaohsiung Medical University, Kaohsiung 807, Taiwan.
| | | | | | | | | | | |
Collapse
|
17
|
Bernatchez S, Szymanski CM, Ishiyama N, Li J, Jarrell HC, Lau PC, Berghuis AM, Young NM, Wakarchuk WW. A single bifunctional UDP-GlcNAc/Glc 4-epimerase supports the synthesis of three cell surface glycoconjugates in Campylobacter jejuni. J Biol Chem 2004; 280:4792-802. [PMID: 15509570 DOI: 10.1074/jbc.m407767200] [Citation(s) in RCA: 94] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The major cell-surface carbohydrates (lipooligosaccharide, capsule, and glycoprotein N-linked heptasaccharide) of Campylobacter jejuni NCTC 11168 contain Gal and/or GalNAc residues. GalE is the sole annotated UDP-glucose 4-epimerase in this bacterium. The presence of GalNAc residues in these carbohydrates suggested that GalE might be a UDP-GlcNAc 4-epimerase. GalE was shown to epimerize UDP-Glc and UDP-GlcNAc in coupled assays with C. jejuni glycosyltransferases and in sugar nucleotide epimerization equilibria studies. Thus, GalE possesses UDP-GlcNAc 4-epimerase activity and was renamed Gne. The Km(app) values of a purified MalE-Gne fusion protein for UDP-GlcNAc and UDP-GalNAc are 1087 and 1070 microm, whereas those for UDP-Glc and UDP-Gal are 780 and 784 microm. The kcat and kcat/Km(app) values were three to four times higher for UDP-GalNAc and UDP-Gal than for UDP-GlcNAc and UDP-Glc. The comparison of the kinetic parameters of MalE-Gne to those of other characterized bacterial UDP-GlcNAc 4-epimerases indicated that Gne is a bifunctional UDP-GlcNAc/Glc 4-epimerase. The UDP sugar-binding site of Gne was modeled by using the structure of the UDP-GlcNAc 4-epimerase WbpP from Pseudomonas aeruginosa. Small differences were noted, and these may explain the bifunctional character of the C. jejuni Gne. In a gne mutant of C. jejuni, the lipooligosaccharide was shown by capillary electrophoresis-mass spectrometry to be truncated by at least five sugars. Furthermore, both the glycoprotein N-linked heptasaccharide and capsule were no longer detectable by high resolution magic angle spinning NMR. These data indicate that Gne is the enzyme providing Gal and GalNAc residues with the synthesis of all three cell-surface carbohydrates in C. jejuni NCTC 11168.
Collapse
Affiliation(s)
- Stéphane Bernatchez
- Institute for Biological Sciences, National Research Council of Canada, Ottawa, Ontario K1A 0R6, Canada
| | | | | | | | | | | | | | | | | |
Collapse
|
18
|
Read JA, Ahmed RA, Morrison JP, Coleman WG, Tanner ME. The mechanism of the reaction catalyzed by ADP-beta-L-glycero-D-manno-heptose 6-epimerase. J Am Chem Soc 2004; 126:8878-9. [PMID: 15264802 DOI: 10.1021/ja0485659] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
ADP-l-glycero-d-manno-heptose 6-epimerase (AGME, RfaD) is a bacterial enzyme that is involved in lipopolysaccharide biosynthesis and interconverts ADP-beta-l-glycero-d-manno-heptose (ADP-l,d-Hep) with ADP-beta-d-glycero-d-manno-heptose (ADP-d,d-Hep). AGME is known to require a tightly bound NADP+ cofactor for activity and presumably employs a mechanism involving transient oxidation of the substrate. Four mechanistic possibilities are considered that involve transient oxidation at either C-7' ', C-6' ', or C-4' ' of the heptose nucleotide. In this contribution, the use of solvent isotope incorporation studies and alternate substrates provides strong evidence for a mechanism involving nonstereospecific oxidation/reduction directly at C-6' '. It was found that the epimerization proceeds without any detectable incorporation of solvent-derived deuterium or 18O-isotope into the product. This argues against mechanisms involving either proton transfers at carbon or dehydration/rehydration events. In addition, the deoxygenated analogues, 7' '-deoxy-ADP-l,d-Hep and 4' '-deoxy-ADP-l,d-Hep, were both found to serve as substrates for the enzyme, indicating that oxidation at either C-7' ' or C-4' ' is not required for catalysis.
Collapse
Affiliation(s)
- Jay A Read
- Department of Chemistry, University of British Columbia, Vancouver, British Columbia, Canada
| | | | | | | | | |
Collapse
|
19
|
Lindner AB, Kim SH, Schindler DG, Eshhar Z, Tawfik DS. Esterolytic antibodies as mechanistic and structural models of hydrolases-a quantitative analysis. J Mol Biol 2002; 320:559-72. [PMID: 12096909 DOI: 10.1016/s0022-2836(02)00418-7] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
Abstract
Understanding enzymes quantitatively and mimicking their remarkable catalytic efficiency is a paramount challenge. Here, we applied esterolytic antibodies (the D-Abs) to dissect and quantify individual elements of enzymatic catalysis such as transition state (TS) stabilization, nucleophilic reactivity and conformational changes. Kinetic and mutagenic analysis of the D-Abs were combined with existing structural evidence to show that catalysis by the D-Abs is driven primarily by stabilization of the tetrahedral oxyanionic intermediate of ester hydrolysis formed by the nucleophilic attack of an exogenous (solution) hydroxide anion. The side-chain of TyrH100d is shown to be the main H-bond donor of the D-Abs oxyanion hole. The pH-rate and pH-binding profiles indicate that the strength of this H-bond increases dramatically as the neutral substrate develops into the oxyanionic TS, resulting in TS stabilization of 5-7 kcal/mol, which is comparable to oxyanionic TS stabilization in serine hydrolases. We show that the rate of the exogenous (intermolecular) nucleophilic attack can be enhanced by 2000-fold by replacing the hydroxide nucleophile with peroxide, an alpha-nucleophile that is much more reactive than hydroxide. In the presence of peroxide, the rate saturates (k(cat)(max)) at 6 s(-1). This rate-ceiling appears to be dictated by the rate of the induced-fit conformational rearrangement leading to the active antibody-TS complex. The selective usage of negatively charged exogenous nucleophiles by the D-Abs led to the identification of a positively charged channel. Imprinted by the negatively-charged TS-analogue against which these antibodies were elicited, this channel presumably directs the nucleophile to the antibody-bound substrate. Our findings are discussed in comparison with serine esterases and, in particular, with cocaine esterase (cocE), which possesses a tyrosine based oxyanion hole.
Collapse
Affiliation(s)
- Ariel B Lindner
- Department of Immunology, Weizmann Institute of Science, Rehovot 76100, Israel
| | | | | | | | | |
Collapse
|
20
|
Allard STM, Beis K, Giraud MF, Hegeman AD, Gross JW, Wilmouth RC, Whitfield C, Graninger M, Messner P, Allen AG, Maskell DJ, Naismith JH. Toward a structural understanding of the dehydratase mechanism. Structure 2002; 10:81-92. [PMID: 11796113 DOI: 10.1016/s0969-2126(01)00694-3] [Citation(s) in RCA: 82] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
Abstract
dTDP-D-glucose 4,6-dehydratase (RmlB) was first identified in the L-rhamnose biosynthetic pathway, where it catalyzes the conversion of dTDP-D-glucose into dTDP-4-keto-6-deoxy-D-glucose. The structures of RmlB from Salmonella enterica serovar Typhimurium in complex with substrate deoxythymidine 5'-diphospho-D-glucose (dTDP-D-glucose) and deoxythymidine 5'-diphosphate (dTDP), and RmlB from Streptococcus suis serotype 2 in complex with dTDP-D-glucose, dTDP, and deoxythymidine 5'-diphospho-D-pyrano-xylose (dTDP-xylose) have all been solved at resolutions between 1.8 A and 2.4 A. The structures show that the active sites are highly conserved. Importantly, the structures show that the active site tyrosine functions directly as the active site base, and an aspartic and glutamic acid pairing accomplishes the dehydration step of the enzyme mechanism. We conclude that the substrate is required to move within the active site to complete the catalytic cycle and that this movement is driven by the elimination of water. The results provide insight into members of the SDR superfamily.
Collapse
Affiliation(s)
- Simon T M Allard
- Centre for Biomolecular Sciences, North Haugh, The University, St. Andrews, Fife KY16 9ST, Scotland, United Kingdom
| | | | | | | | | | | | | | | | | | | | | | | |
Collapse
|