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Structure Function Relationships in Pyrimidine Degrading and Biocatalytic Enzymes, and Their Implications for Cancer Therapy and Green Chemistry
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - BMC, Biochemistry. Uppsala University.
2018 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

This thesis includes the work of two separate projects, studies on pyrimidine degrading enzymes and studies on in vitro evolved enzymes. The common denominator of both projects was the use of structural information to explain functional effects, observed in the studied biocatalysts.

In humans, and other eukaryotic organisms, the nucleobases uracil and thymine are catabolized by the reductive pyrimidine degradation pathway. This pathway is one of the factors that control the pyrimidine nucleotide concentrations in a cell. Furthermore, it is the main clearance route for pyrimidine analogues, often used as cancer drugs, like 5-fluorouracil and other fluoropyrimidines. Deficiencies in any of the enzymes, involved in this pathway, can lead to a wide range of neurological disorders, and possibly fatal fluoropyrimidine toxicity in cancer patients. Two out of the three involved enzymes, dihydropyrimidine dehydrogenase (DPD) and β-ureidopropionase (βUP), were studied in the first project of this thesis. This resulted in the first crystal structure of a human β-ureidopropionase variant, which could be used to explain functional characteristics of the enzyme. Structural analyses on novel DPD variants, found in patients suffering from DPD deficiency, could explain the decrease in catalytic activity of these enzyme variants. This strategy, of using structural information to predict functional effects from sequential mutations, has the potential to be used as a cheap and fast first assessment of possible deficiencies in this pathway.

Enzymes are, however, not only involved in many diseases, but also used for industrial applications. The substitution of classical organic synthetic reactions with enzyme catalyzed reactions usually has a beneficial influence on environmental pollution, as illustrated in the principles of Green Chemistry. The major drawback of the use of enzymes for these purposes is their natural selectivity towards a small group of possible substrates and products, which often do not have the desired composition or conformation for an industrial application. In order to improve an enzyme for industrial purposes, the alcohol dehydrogenase ADH-A, from Rhodococcus ruber, was subjected to a semi-rational approach of directed evolution, using iterative saturation mutagenesis (ISM), in the second project of this thesis. This resulted in different enzyme variants that showed the desired improvements in activity. Most functional improvements could be rationalized with the help of structural information and molecular dynamics simulations. This showed that artificial protein design has the potential to produce enzyme variants capable of substituting many organic synthetic reactions, and that structural information can play a key role in the designing process.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2018. , p. 129
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1633
Keywords [en]
β-Ureidopropionase, Dihydropyrimidine Dehydrogenase, Alcohol Dehydrogenase, Pyrimidine catabolism, 5-Fluorouracil, CASTing, X-ray Crystallography
National Category
Biochemistry and Molecular Biology Structural Biology
Identifiers
URN: urn:nbn:se:uu:diva-341639ISBN: 978-91-513-0240-9 (print)OAI: oai:DiVA.org:uu-341639DiVA, id: diva2:1183535
Public defence
2018-04-06, B41, Husargatan 3, Uppsala, Sweden, 09:30 (English)
Opponent
Supervisors
Available from: 2018-03-15 Created: 2018-02-18 Last updated: 2018-04-24
List of papers
1. Characterization and structure determination of human β-ureidopropionase reveal pH-dependent regulation by ligand-induced changes in oligomerization
Open this publication in new window or tab >>Characterization and structure determination of human β-ureidopropionase reveal pH-dependent regulation by ligand-induced changes in oligomerization
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(English)Manuscript (preprint) (Other academic)
Keywords
β-alanine synthase, β-ureidopropionase, β-alanine, pyrimidine degradation, fluoropyrimidine toxicity
National Category
Biochemistry and Molecular Biology Structural Biology
Research subject
Biochemistry
Identifiers
urn:nbn:se:uu:diva-341994 (URN)
Available from: 2018-02-18 Created: 2018-02-18 Last updated: 2018-02-21
2. Severe fluoropyrimidine toxicity due to novel and rare DPYD missense mutations, deletion and genomic amplification affecting DPD activity and mRNA splicing
Open this publication in new window or tab >>Severe fluoropyrimidine toxicity due to novel and rare DPYD missense mutations, deletion and genomic amplification affecting DPD activity and mRNA splicing
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2017 (English)In: Biochimica et Biophysica Acta, ISSN 0006-3002, E-ISSN 1878-2434, Vol. 1863, no 3, p. 721-730Article in journal (Refereed) Published
Abstract [en]

Dihydropyrimidine dehydrogenase (DPD) is the initial and rate-limiting enzyme in the catabolism of 5-fluorouracil (5FU). Genetic variations in DPD have emerged as predictive risk factors for severe fluoropyrimidine toxicity. Here, we report novel and rare genetic variants underlying DPD deficiency in 9 cancer patients presenting with severe fluoropyrimidine-associated toxicity. All patients possessed a strongly reduced DPD activity, ranging from 9 to 53% of controls. Analysis of the DPD gene (DPYD) showed the presence of 21 variable sites including 4 novel and 4 very rare aberrations: 3 missense mutations, 2 splice-site mutations, 1 intronic mutation, a deletion of 21 nucleotides and a genomic amplification of exons 9-12. Two novel/rare variants (c.2843T>C, c.321+1G>A) were present in multiple, unrelated patients. Functional analysis of recombinantly-expressed DPD mutants carrying the p.I948T and p.G284V mutation showed residual DPD activities of 30% and 0.5%, respectively. Analysis of a DPD homology model indicated that the p.I948T and p.G284V mutations may affect electron transfer and the binding of FAD, respectively. cDNA analysis showed that the c.321+1G>A mutation in DPYD leads to skipping of exon 4 immediately upstream of the mutated splice-donor site in the process of DPD pre-mRNA splicing. A lethal toxicity in two DPD patients suggests that fluoropyrimidines combined with other therapies such as radiotherapy might be particularly toxic for DPD deficient patients. Our study advocates a more comprehensive genotyping approach combined with phenotyping strategies for upfront screening for DPD deficiency to ensure the safe administration of fluoropyrimidines.

Keywords
Dihydropyrimidine dehydrogenase, DPYD, 5-Fluorouracil, Capecitabine, Pharmacogenetics, Toxicity
National Category
Medical Genetics
Identifiers
urn:nbn:se:uu:diva-312179 (URN)10.1016/j.bbadis.2016.12.010 (DOI)000394190300009 ()28024938 (PubMedID)
Available from: 2017-01-06 Created: 2017-01-06 Last updated: 2018-02-18
3. Genome sequencing reveals a novel genetic mechanism underlying dihydropyrimidine dehydrogenase deficiency: A novel missense variant c.1700G > A and a large intragenic inversion in DPYD spanning intron 8 to intron 12
Open this publication in new window or tab >>Genome sequencing reveals a novel genetic mechanism underlying dihydropyrimidine dehydrogenase deficiency: A novel missense variant c.1700G > A and a large intragenic inversion in DPYD spanning intron 8 to intron 12
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2018 (English)In: Human Mutation, ISSN 1059-7794, E-ISSN 1098-1004, Vol. 39, no 7, p. 947-953Article in journal (Refereed) Published
Abstract [en]

Dihydropyrimidine dehydrogenase (DPD) deficiency is associated with a variable clinical presentation. A family with three DPD-deficient patients presented with unusual clinical phenotypes including pregnancy-induced symptoms, transient visual impairment, severe developmental delay, cortical blindness, and delayed myelination in the brain. DPYD Sanger sequencing showed heterozygosity for the c.1905+1G>A mutation and a novel missense variant c.1700G>A (p.G567E). The recombinantly expressed p.G567E DPD variant showed increased temperature lability probably caused by structural rearrangements within the DPD protein. Genome sequencing of the affected son established compound heterozygosity for the c.1700G>A and an imperfect 115,731bp inversion with breakpoints at chr1: 98,113,121 (intron 8) and chr1: 97,997,390 (intron 12) of the DPYD associated with a 4bp deletion (chr1: 97,997,386_97,997,389del). Whole exome and mitochondrial DNA analyses for the mother and daughter did not reveal additional mutated genes of significance. Thus, an inversion in DPYD should be considered in patients with an inconclusive genotype or unusual clinical phenotype.

Keywords
dihydropyrimidine dehydrogenase, DPYD, inversion, whole genome sequencing
National Category
Medicinal Chemistry Structural Biology
Identifiers
urn:nbn:se:uu:diva-342024 (URN)10.1002/humu.23538 (DOI)000434972700006 ()29691939 (PubMedID)
Note

Title of manuscript included in thesis: Genome sequencing reveals a novel genetic mechanism underlying dihydropyrimidine dehydrogenase deficiency: a large intragenic inversion in DPYD spanning intron 8 to intron 12

Available from: 2018-02-18 Created: 2018-02-18 Last updated: 2018-08-31Bibliographically approved
4. Relaxation of Nonproductive Binding and Increased Rate of Coenzyme Release in an Alcohol Dehydrogenase Increases Turnover With a Non-Preferred Alcohol Enantiomer
Open this publication in new window or tab >>Relaxation of Nonproductive Binding and Increased Rate of Coenzyme Release in an Alcohol Dehydrogenase Increases Turnover With a Non-Preferred Alcohol Enantiomer
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2017 (English)In: The FEBS Journal, ISSN 1742-464X, E-ISSN 1742-4658, Vol. 284, no 22, p. 3895-3914Article in journal (Refereed) Published
Abstract [en]

Alcohol dehydrogenase A (ADH-A) from Rhodococcus ruber DSM 44541 is a promising biocatalyst for redox transformations of arylsubstituted sec-alcohols and ketones. The enzyme is stereoselective in the oxidation of 1-phenylethanol with a 300-fold preference for the (S)-enantiomer. The low catalytic efficiency with (R)-1-phenylethanol has been attributed to nonproductive binding of this substrate at the active site. Aiming to modify the enantioselectivity, to rather favor the (R)-alcohol, and also test the possible involvement of nonproductive substrate binding as a mechanism in substrate discrimination, we performed directed laboratory evolution of ADH-A. Three targeted sites that contribute to the active-site cavity were exposed to saturation mutagenesis in a stepwise manner and the generated variants were selected for improved catalytic activity with (R)-1-phenylethanol. After three subsequent rounds of mutagenesis, selection and structure-function analysis of isolated ADH-A variants, we conclude: (1) W295 has a key role as a structural determinant in the discrimination between (R)- and (S)-1-phenylethanol and a W295A substitution fundamentally changes the stereoselectivity of the protein. One observable effect is a faster rate of NADH release, which changes the rate-limiting step of the catalytic cycle from coenzyme release to hydride transfer. (2) The obtained change in enantiopreference, from the (S)- to the (R)-alcohol, can be partly explained by a shift in the nonproductive substrate binding modes.

Keywords
alcohol dehydrogenase, biocatalysis, stereoselectivity, directed evolution, crystal structures, enzyme kinetics
National Category
Biochemistry and Molecular Biology
Identifiers
urn:nbn:se:uu:diva-318981 (URN)10.1111/febs.14279 (DOI)000415877100011 ()
Funder
Swedish Research Council, 621-2011-6055
Available from: 2017-03-30 Created: 2017-03-30 Last updated: 2019-10-21Bibliographically approved
5. Directed Evolution of Alcohol Dehydrogenase for Improved Stereoselective Redox Transformations of 1-Phenylethane-1,2-Diol and Its Corresponding Acyloin
Open this publication in new window or tab >>Directed Evolution of Alcohol Dehydrogenase for Improved Stereoselective Redox Transformations of 1-Phenylethane-1,2-Diol and Its Corresponding Acyloin
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2018 (English)In: Biochemistry, ISSN 0006-2960, E-ISSN 1520-4995, Vol. 57, p. 1059-1062Article in journal (Refereed) Published
Abstract [en]

Laboratory evolution of alcohol dehydrogenase produced enzyme variants with improved turnover numbers with a vicinal 1,2-diol and its corresponding hydroxyketone. Crystal structure and transient kinetics analysis aids in rationalizing the new functions of these variants.

National Category
Biochemistry and Molecular Biology
Research subject
Biochemistry
Identifiers
urn:nbn:se:uu:diva-340574 (URN)10.1021/acs.biochem.8b00055 (DOI)000426013300003 ()29384657 (PubMedID)
Funder
Stiftelsen Olle Engkvist Byggmästare, 183-358
Available from: 2018-01-31 Created: 2018-01-31 Last updated: 2019-10-21Bibliographically approved
6. Stereoselectivity in Catalyzed Transformation of a 1,2-Disubstituted Vicinal Diol and the Corresponding Diketone by Wild Type and Laboratory Evolved Alcohol Dehydrogenases
Open this publication in new window or tab >>Stereoselectivity in Catalyzed Transformation of a 1,2-Disubstituted Vicinal Diol and the Corresponding Diketone by Wild Type and Laboratory Evolved Alcohol Dehydrogenases
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(English)In: Article in journal (Other academic) Submitted
National Category
Biochemistry and Molecular Biology
Identifiers
urn:nbn:se:uu:diva-318982 (URN)
Available from: 2017-03-30 Created: 2017-03-30 Last updated: 2018-02-18

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