1
|
Svegelj MB, Stojan J, Rižner TL. The role of Ala231 and Trp227 in the substrate specificities of fungal 17β-hydroxysteroid dehydrogenase and trihydroxynaphthalene reductase: Steroids versus smaller substrates. J Steroid Biochem Mol Biol 2012; 129:92-8. [PMID: 21439381 DOI: 10.1016/j.jsbmb.2011.03.019] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/03/2011] [Revised: 03/04/2011] [Accepted: 03/12/2011] [Indexed: 11/17/2022]
Abstract
17β-Hydroxysteroid dehydrogenase and trihydroxynaphthalene reductase from the fungus Curvularia lunata (teleomorph: Cochliobolus lunatus; 17β-HSDcl and 3HNR, respectively) are two homologous short-chain dehydrogenase/reductase proteins that are 58% identical and have 86% similar amino acids. The minor differences in their substrate-binding regions are believed to be crucial for their substrate specificities. 3HNR shows high affinity for substrates with two rings, like trihydroxynaphthalene and 2,3-dihydro-2,5-dihydroxy-4H-benzopyran-4-one (DDBO), while 17β-HSDcl can accommodate ligands with four rings, like steroids. In the present study, we examined the role of Ala231 in 17β-HSDcl and Trp227 in 3HNR, as the potential key amino acids in the determination of substrate recognition based on size. We constructed Ala231Trp 17β-HSDcl and Trp227Ala 3HNR mutant proteins and used spectrophotometric analyses to compare their catalytic activities with those of the wild-type enzymes, for oxidation of 4-estrene-17β-ol-3-one and DDBO and for reduction of 4-estrene-3,17-dione and 9,10-phenanthrenequinone (PQ). The Ala231Trp side-chain substitution in 17β-HSDcl abolished and decreased (by 14.6-fold) the initial rates for steroid oxidation and reduction, respectively, while the initial rate for PQ reduction was increased 5.6-fold. The bulky Trp227Ala side-chain substitution in 3HNR enabled oxidation of 4-estrene-17β-ol-3-one, increased the initial rates for reduction of 4-estrene-3,17-dione and PQ by 4.5-fold and 1.5-fold, respectively, while the initial rate for DDBO oxidation was decreased 4.1-fold. Our TLC analysis and docking simulations also support these findings. Our study thus confirms the important roles of Ala231 in 17β-HSDcl and Trp227 in 3HNR, for the selection between larger and smaller substrates. Article from a special issue on steroids and microorganisms.
Collapse
|
2
|
Frandsen RJN, Schütt C, Lund BW, Staerk D, Nielsen J, Olsson S, Giese H. Two novel classes of enzymes are required for the biosynthesis of aurofusarin in Fusarium graminearum. J Biol Chem 2011; 286:10419-28. [PMID: 21296881 DOI: 10.1074/jbc.m110.179853] [Citation(s) in RCA: 64] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Previous studies have reported the functional characterization of 9 out of 11 genes found in the gene cluster responsible for biosynthesis of the polyketide pigment aurofusarin in Fusarium graminearum. Here we reanalyze the function of a putative aurofusarin pump (AurT) and the two remaining orphan genes, aurZ and aurS. Targeted gene replacement of aurZ resulted in the discovery that the compound YWA1, rather than nor-rubrofusarin, is the primary product of F. graminearum polyketide synthase 12 (FgPKS12). AurZ is the first representative of a novel class of dehydratases that act on hydroxylated γ-pyrones. Replacement of the aurS gene resulted in accumulation of rubrofusarin, an intermediate that also accumulates when the GIP1, aurF, or aurO genes in the aurofusarin cluster are deleted. Based on the shared phenotype and predicted subcellular localization, we propose that AurS is a member of an extracellular enzyme complex (GIP1-AurF-AurO-AurS) responsible for converting rubrofusarin into aurofusarin. This implies that rubrofusarin, rather than aurofusarin, is pumped across the plasma membrane. Replacement of the putative aurofusarin pump aurT increased the rubrofusarin-to- aurofusarin ratio, supporting that rubrofusarin is normally pumped across the plasma membrane. These results provide functional information on two novel classes of proteins and their contribution to polyketide pigment biosynthesis.
Collapse
Affiliation(s)
- Rasmus J N Frandsen
- Department of Agriculture and Ecology, Faculty of Life Sciences, University of Copenhagen, DK-1870 Frederiksberg, Denmark.
| | | | | | | | | | | | | |
Collapse
|
3
|
Brunskole M, Zorko K, Kerbler V, Martens S, Stojan J, Gobec S, Lanišnik Rižner T. Trihydroxynaphthalene reductase of Curvularia lunata—A target for flavonoid action? Chem Biol Interact 2009; 178:259-67. [DOI: 10.1016/j.cbi.2008.10.023] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/06/2008] [Revised: 09/25/2008] [Accepted: 10/01/2008] [Indexed: 10/21/2022]
|
4
|
Brunskole M, Štefane B, Zorko K, Anderluh M, Stojan J, Lanišnik Rižner T, Gobec S. Towards the first inhibitors of trihydroxynaphthalene reductase from Curvularia lunata: Synthesis of artificial substrate, homology modelling and initial screening. Bioorg Med Chem 2008; 16:5881-9. [DOI: 10.1016/j.bmc.2008.04.066] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/11/2008] [Revised: 04/19/2008] [Accepted: 04/25/2008] [Indexed: 11/26/2022]
|
5
|
Cassetta A, Büdefeld T, Rizner TL, Kristan K, Stojan J, Lamba D. Crystallization, X-ray diffraction analysis and phasing of 17beta-hydroxysteroid dehydrogenase from the fungus Cochliobolus lunatus. Acta Crystallogr Sect F Struct Biol Cryst Commun 2005; 61:1032-4. [PMID: 16511227 PMCID: PMC1978160 DOI: 10.1107/s1744309105034949] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/07/2005] [Accepted: 10/26/2005] [Indexed: 11/11/2022]
Abstract
17beta-Hydroxysteroid dehydrogenase from the filamentous fungus Cochliobolus lunatus (17beta-HSDcl) is an NADP(H)-dependent enzyme that preferentially catalyses the oxidoreduction of oestrogens and androgens. The enzyme belongs to the short-chain dehydrogenase/reductase superfamily and is the only fungal hydroxysteroid dehydrogenase known to date. 17beta-HSDcl has recently been characterized and cloned and has been the subject of several functional studies. Although several hypotheses on the physiological role of 17beta-HSDcl in fungal metabolism have been formulated, its function is still unclear. An X-ray crystallographic study has been undertaken and the optimal conditions for crystallization of 17beta-HSDcl (apo form) were established, resulting in well shaped crystals that diffracted to 1.7 A resolution. The space group was identified as I4(1)22, with unit-cell parameters a = b = 67.14, c = 266.77 A. Phasing was successfully performed by Patterson search techniques. A catalytic inactive mutant Tyr167Phe was also engineered, expressed, purified and crystallized for functional and structural studies.
Collapse
Affiliation(s)
- Alberto Cassetta
- Institute of Crystallography, CNR, Trieste Outstation, Area Science Park-Basovizza, S.S.14, I-34012 Trieste, Italy.
| | | | | | | | | | | |
Collapse
|
6
|
Lanisnik Rizner T, Wheeler MH. Melanin biosynthesis in the fungus Curvularia lunata (teleomorph: Cochliobolus lunatus). Can J Microbiol 2003; 49:110-9. [PMID: 12718399 DOI: 10.1139/w03-016] [Citation(s) in RCA: 50] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Curvularia lunata (teleomorph: Cochliobolus lunatus) is a known plant and human pathogen. Tricyclazole, a specific inhibitor of pentaketide melanin biosynthesis, blocked the biosynthesis of melanin in Curvularia lunata and caused the accumulation of the melanin metabolites flaviolin and 2-hydroxyjuglone. This showed that melanin in Curvularia lunata is produced by a pentaketide pathway from 1,8-dihydroxynaphthalene. The 1,3,8-trihydroxynaphthalene reductase (3HNR) gene, associated with the melanin pathway of Curvularia lunata, was identified and characterized. An alignment of 3HNR sequences enabled the design of primers covering conserved regions. A PCR-amplified fragment of Curvularia lunata genomic DNA was used for screening the cDNA library. Three independent cDNA clones revealed an 801-bp open reading frame encoding a 267 amino acid protein. The protein was expressed in Escherichia coli and purified to homogeneity. The predicted amino acid sequence of the 28.6-kDa protein demonstrated homology to other fungal 3HNR and other members of the short-chain dehydrogenase super family. Northern analyses revealed that 3HNR from Curvularia lunata is expressed synchronously with melanization after 3 days of Curvularia lunata growth in malt extract medium. No 3HNR reductase gene expression nor melanization was observed when Curvularia lunata was grown in yeast nitrogen base medium.
Collapse
Affiliation(s)
- Tea Lanisnik Rizner
- Institute of Biochemistry, Medical Faculty, University of Ljubljana, Vrazov trg 2, 1000 Ljubljana, Slovenia.
| | | |
Collapse
|
7
|
Rizner TL, Adamski J, Stojan J. 17Beta-hydroxysteroid dehydrogenase from Cochliobolus lunatus: model structure and substrate specificity. Arch Biochem Biophys 2001; 384:255-62. [PMID: 11368312 DOI: 10.1006/abbi.2000.2064] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
A homology-built structural model of 17beta-hydroxysteroid dehydrogenase from the fungus Cochliobolus lunatus, a member of the short-chain dehydrogenase/reductase family, was worked out using the known three-dimensional structure of trihydroxynaphthalene reductase (EC 1.3.1.50) from Magnaporthe grisea as a template. Due to 61% sequence identity, the model also revealed a similar backbone trace. On the basis of qualitative thin-layer chromatography and comparative kinetic tests of the activity toward various potential steroid substrates, we conclude that androgens are more efficiently converted than estrogens. Their specific oxidoreduction predominantly occurs at the C17 position while no significant conversion at C3 and C20 was determined. Additionally, a thousand times effective inhibition by 5-methyl-(1,2,4)-triazolo[3,4-b]benzothiazole and no activity toward 2,3-dihydro-2,5-dihydroxy-4H-benzopyran-4-one indicate distinct specificies of 17beta-hydroxysteroid dehydrogenase from the fungus C. lunatus and trihydroxynaphthalene reductase. The results of the analysis of progress curve measurements for the forward and backward reactions are consistent with the Theorell-Chance reaction mechanism also predicted from the structural model. In accordance with these results, 4-androstene-3,17-dione was docked into the enzyme active site using molecular modeling and dynamics calculations.
Collapse
Affiliation(s)
- T L Rizner
- Institute of Biochemistry, Medical Faculty, University of Ljubljana, Slovenia
| | | | | |
Collapse
|
8
|
Lanisnik Rizner T, Stojan J, Adamski J. Searching for the physiological function of 17beta-hydroxysteroid dehydrogenase from the fungus Cochliobolus lunatus: studies of substrate specificity and expression analysis. Mol Cell Endocrinol 2001; 171:193-8. [PMID: 11165029 DOI: 10.1016/s0303-7207(00)00424-x] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
17beta-hydroxysteroid dehydrogenase from the filamentous fungus Cochliobolus lunatus (17beta-HSDcl) has recently been characterized. Since its function is still unclear, we performed substrate specificity studies to obtain some indications about its physiological function. Different steroids were studied as putative substrates of recombinant 17beta-HSDcl, androgens and estrogens, brassinosteroids, and the fungal steroid herbarulid. Among these androgens and estrogens were most efficiently converted. The following substrates in decreasing order were best reduced: 4-estrene-3,17-dione, 5alpha-androstane-3,17-dione, 4-androstene-3,17-dione and estrone. Two typical inhibitors were tested: carbenoxolone--a representative inhibitor of the SDR family and quercetin--a diagnostic inhibitor of carbonyl reductases. Among these two quercetin was more efficient. Expression studies revealed that 17beta-HSDcl is mainly expressed in the stationary phase of growth indicating its possible involvement in secondary metabolism.
Collapse
Affiliation(s)
- T Lanisnik Rizner
- Institute of Biochemistry, Medical Faculty, University of Ljubljana, Vrazov trg 2, 1000, Ljubljana, Slovenia.
| | | | | |
Collapse
|
9
|
Thompson JE, Fahnestock S, Farrall L, Liao DI, Valent B, Jordan DB. The second naphthol reductase of fungal melanin biosynthesis in Magnaporthe grisea: tetrahydroxynaphthalene reductase. J Biol Chem 2000; 275:34867-72. [PMID: 10956664 DOI: 10.1074/jbc.m006659200] [Citation(s) in RCA: 104] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Mutants of Magnaporthe grisea harboring a defective gene for 1,3, 8-trihydroxynaphthalene reductase retain the capability to produce scytalone, thus suggesting the existence of a second naphthol reductase that can catalyze the reduction of 1,3,6, 8-tetrahydroxynaphthalene to scytalone within the fungal melanin biosynthetic pathway. The second naphthol reductase gene was cloned from M. grisea by identification of cDNA fragments with weak homology to the cDNA of trihydroxynaphthalene reductase. The amino acid sequence for the second naphthol reductase is 46% identical to that of trihydroxynaphthalene reductase. The second naphthol reductase was produced in Esherichia coli and purified to homogeneity. Substrate competition experiments indicate that the second reductase prefers tetrahydroxynaphthalene over trihydroxynaphthalene by a factor of 310; trihydroxynaphthalene reductase prefers trihydroxynaphthalene over tetrahydroxynaphthalene by a factor of 4.2. On the basis of the 1300-fold difference in substrate specificities between the two reductases, the second reductase is designated tetrahydroxynaphthalene reductase. Tetrahydroxynaphthalene reductase has a 200-fold larger K(i) for the fungicide tricyclazole than that of trihydroxynaphthalene reductase, and this accounts for the latter enzyme being the primary physiological target of the fungicide. M. grisea mutants lacking activities for both trihydroxynaphthalene and tetrahydroxynaphthalene reductases do not produce scytalone, indicating that there are no other metabolic routes to scytalone.
Collapse
Affiliation(s)
- J E Thompson
- DuPont Agricultural Products, Stine-Haskell Research Center, Newark, Delaware 19714, USA
| | | | | | | | | | | |
Collapse
|
10
|
Firestine SM, Salinas F, Nixon AE, Baker SJ, Benkovic SJ. Using an AraC-based three-hybrid system to detect biocatalysts in vivo. Nat Biotechnol 2000; 18:544-7. [PMID: 10802623 DOI: 10.1038/75414] [Citation(s) in RCA: 45] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
Recent methods to create large libraries of proteins have greatly advanced the discovery of proteins with novel functions. However, one limitation in the discovery of new biocatalysts is the screening or selection methods employed to find enzymes from these libraries. We have developed a potentially general method termed QUEST (QUerying for EnzymeS using the Three-hybrid system), which allows the construction of an easily screened or selected phenotype for, in theory, any type of enzymatic reaction. The method couples the in vivo concentration of an enzyme's substrate to changes in the transcriptional level of a reporter operon. Using the arabinose operon activator AraC, we constructed a system capable of detecting the fungal enzyme scytalone dehydratase (SD) in bacteria, and demonstrated its sensitivity and usefulness in library screening.
Collapse
Affiliation(s)
- S M Firestine
- Department of Chemistry, The Pennsylvania State University, University Park, PA 16802, USA
| | | | | | | | | |
Collapse
|
11
|
Liao DI, Basarab GS, Gatenby AA, Jordan DB. Selection of a potent inhibitor of trihydroxynaphthalene reductase by sorting disease control data. Bioorg Med Chem Lett 2000; 10:491-4. [PMID: 10743955 DOI: 10.1016/s0960-894x(00)00037-8] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Abstract
Compounds that control rice blast, but not other crop diseases, were selected for testing as inhibitors of trihydroxynaphthalene reductase of the fungal melanin biosynthetic pathway. A potent inhibitor of the enzyme (2) (Ki = 25 nM) was identified. An X-ray structure of the enzyme-NADPH-2 complex was determined at 2.1 A resolution.
Collapse
Affiliation(s)
- D I Liao
- DuPont Central Research and Development, Experimental Station, Wilmington DE, 19880, USA
| | | | | | | |
Collapse
|
12
|
Basarab GS, Jordan DB. Wild-type enzyme as a reporter of inhibitor binding by catalytically impaired mutant enzymes. Biochem Biophys Res Commun 1999; 263:617-20. [PMID: 10512727 DOI: 10.1006/bbrc.1999.1423] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
A method for the determination of inhibition constants for catalytically-debilitated mutant enzymes is described. The inhibitor is partitioned between the mutant and wild-type enzymes. Catalytic rates of the wild-type enzyme are used as the signal of inhibitor binding to the mutant enzyme. The method is validated with scytalone dehydratase, the Y50F mutant, and a potent inhibitor. The K(i) value for Y50F determined by this method is 0.49 +/- 0.10 nM. The K(i) value determined using the Y50F catalytic report for inhibitor binding in the absence of wild-type enzyme is 0.20 +/- 0.030 nM. The wild-type enzyme binds the inhibitor ten-fold less tightly, thus indicating that the hydrogen-bonding interaction between the Y50 hydroxyl group and the inhibitor (suggested by X-ray crystallography) is weak. The method is most useful when the catalytic activity of the wild-type enzyme is the most sensitive report of inhibitor binding and the mutant enzyme is greatly crippled in catalytic activity.
Collapse
Affiliation(s)
- G S Basarab
- DuPont Agricultural Products, Stine-Haskell Research Center, 1094 Elkton Road, Newark, Delaware, 19714-0030, USA
| | | |
Collapse
|
13
|
Jennings LD, Wawrzak Z, Amorose D, Schwartz RS, Jordan DB. A new potent inhibitor of fungal melanin biosynthesis identified through combinatorial chemistry. Bioorg Med Chem Lett 1999; 9:2509-14. [PMID: 10498198 DOI: 10.1016/s0960-894x(99)00424-2] [Citation(s) in RCA: 23] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
Abstract
A new fungicide lead has been identified by in vitro screening of a focused combinatorial library. Amides (768) were synthesized in pools of four and assayed as inhibitors of scytalone dehydratase. Deconvolution of one of the most active pools led to the discovery of a potent inhibitor of the enzyme 3b (K(i) = 26 pM), which has fungicidal properties.
Collapse
Affiliation(s)
- L D Jennings
- Dupont Agricultural Products, Stine Haskell Research Center, Newark, DE 19714, USA
| | | | | | | | | |
Collapse
|
14
|
Jordan DB, Basarab GS, Steffens JJ, Lundqvist T, Pfrogner BR, Schwartz RS, Wawrzak Z. Catalytic mechanism of scytalone dehydratase fromMagnaporthe grisea. ACTA ACUST UNITED AC 1999. [DOI: 10.1002/(sici)1096-9063(199903)55:3<277::aid-ps893>3.0.co;2-1] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
|
15
|
Wawrzak Z, Sandalova T, Steffens JJ, Basarab GS, Lundqvist T, Lindqvist Y, Jordan DB. High-resolution structures of scytalone dehydratase-inhibitor complexes crystallized at physiological pH. Proteins 1999; 35:425-39. [PMID: 10382670 DOI: 10.1002/(sici)1097-0134(19990601)35:4<425::aid-prot6>3.0.co;2-1] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Abstract
Scytalone dehydratase is a molecular target of inhibitor design efforts aimed at preventing the fungal disease caused by Magnaporthe grisea. A method for cocrystallization of enzyme with inhibitors at neutral pH has produced several crystal structures of enzyme-inhibitor complexes at resolutions ranging from 1.5 to 2.2 A. Four high resolution structures of different enzyme-inhibitor complexes are described. In contrast to the original X-ray structure of the enzyme, the four new structures have well-defined electron density for the loop region comprising residues 115-119 and a different conformation between residues 154 and 160. The structure of the enzyme complex with an aminoquinazoline inhibitor showed that the inhibitor is in a position to form a hydrogen bond with the amide of the Asn131 side chain and with two water molecules in a fashion similar to the salicylamide inhibitor in the original structure, thus confirming design principles. The aminoquinazoline structure also allows for a more confident assignment of donors and acceptors in the hydrogen bonding network. The structures of the enzyme complexes with two dichlorocyclopropane carboxamide inhibitors showed the two chlorine atoms nearly in plane with the amide side chain of Asn131. The positions of Phe53 and Phe158 are significantly altered in the new structures in comparison to the two structures obtained from crystals grown at acidic pH. The multiple structures help define the mobility of active site amino acids critical for catalysis and inhibitor binding.
Collapse
Affiliation(s)
- Z Wawrzak
- E.I. DuPont de Nemours Life Sciences, Experimental Station, Wilmington, Delaware, USA
| | | | | | | | | | | | | |
Collapse
|
16
|
Nixon AE, Firestine SM, Salinas FG, Benkovic SJ. Rational design of a scytalone dehydratase-like enzyme using a structurally homologous protein scaffold. Proc Natl Acad Sci U S A 1999; 96:3568-71. [PMID: 10097077 PMCID: PMC22334 DOI: 10.1073/pnas.96.7.3568] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
The generation of enzymes to catalyze specific reactions is one of the more challenging problems facing protein engineers. Structural similarities between the enzyme scytalone dehydratase with nuclear transport factor 2 (NTF2) suggested the potential for NTF2 to be re-engineered into a scytalone dehydratase-like enzyme. We introduced four key catalytic residues into NTF2 to create a scytalone dehydratase-like active site. A C-terminal helix found in scytalone dehydratase but absent in NTF2 also was added. Mutant NTF2 proteins were tested for catalytic activity by using a spectroscopic assay. One of the engineered enzymes exhibited catalytic activity with minimal kcat and Km values of 0.125 min-1 and 800 microM, respectively. This level of catalytic activity represents minimally a 150-fold improvement in activity over the background rate for substrate dehydration and a dramatic step forward from the catalytically inert parent NTF2. This work represents one of the few examples of converting a protein scaffold into an enzyme, outside those arising from the induction of catalytic activity into antibodies.
Collapse
Affiliation(s)
- A E Nixon
- 152 Davey Laboratory, Department of Chemistry, Pennsylvania State University, University Park, PA 16802-6300, USA
| | | | | | | |
Collapse
|
17
|
Thompson JE, Jordan DB. Partition analysis of an enzyme acting concurrently upon two substrates in a continuous multiwavelength assay. Anal Biochem 1998; 256:7-13. [PMID: 9466792 DOI: 10.1006/abio.1997.2490] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
We describe a multiwavelength method for measuring an enzyme's discrimination of one substrate over another by continuously monitoring the reactions of the two substrates simultaneously. This method is generally applicable to ultraviolet-visible diode array or rapid-scanning spectrophotometers and the measurement requires a single incubation of enzyme with two substrates. Rates at each of the wavelengths may be fit globally by using a nonlinear least-squares fitting procedure which provides adequate statistical analysis. The specificity of trypsin for N-alpha-benzoyl-L-arginine p-nitroanilide (BRpNA) over N-t-butyloxycarbonyl-L-alanine-p-nitrophenylester (BocApNP) was 2.1 as measured by the multiwavelength partition method and 2.3 by comparing the individual kcat/K(m)'s for the two substrates. Multiwavelength analysis was applied to two enzymes in the biosynthetic pathway for fungal melanin: scytalone dehydratase and trihydroxynaphthalene reductase from Magnaporthea grisea. The specificity of trihydroxynaphthalene reductase for 2,3-dihydro-2,5-dihydroxy-4H-benzopyran-4-one compared to scytalone, a natural substrate for the enzyme, was 95. Scytalone dehydratase was eight-fold more specific for 2,3-dihydro-2,5-dihydroxy-4H-benzopyran-4-one than it was for scytalone. Multiwavelength analysis was also used to measure an equilibrium constant of 0.040 for the reaction ¿dihydroorotate + oxonic acid<-->orotate + dihydrooxonic acid¿ catalyzed by dihydroorotate dehydrogenase. Advantages, limitations, and further applications of this steady-state method, which directly measures relative substrate specificities, are delineated. All studies described in this paper were at pH 7.0 and 25 degrees C.
Collapse
Affiliation(s)
- J E Thompson
- E. I. DuPont de Nemours Agricultural Products, Stine-Haskell Research Center, Newark, Delaware 19714-0030, USA
| | | |
Collapse
|