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Walton CJW, Thiebaut F, Brunzelle JS, Couture JF, Chica RA. Structural Determinants of the Stereoinverting Activity of Pseudomonas stutzeri d-Phenylglycine Aminotransferase. Biochemistry 2018; 57:5437-5446. [PMID: 30153007 DOI: 10.1021/acs.biochem.8b00767] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Aromatic d-amino acids are key precursors for the production of many small molecule therapeutics. Therefore, the development of biocatalytic methods for their synthesis is of great interest. An enzyme that has great potential as a biocatalyst for the synthesis of d-amino acids is the stereoinverting d-phenylglycine aminotransferase (DPAT) from Pseudomonas stutzeri ST-201. This enzyme catalyzes a unique l to d transamination reaction that produces d-phenylglycine and α-ketoglutarate from benzoylformate and l-glutamate, via a mechanism that is poorly understood. Here, we present the crystal structure of DPAT, which shows that the enzyme folds into a two-domain structure representative of class III aminotransferases. Guided by the crystal structure, we performed saturation mutagenesis to probe the substrate binding pockets of the enzyme. These experiments helped us identify two arginine residues (R34 and R407), one in each binding pocket, that are essential to catalysis. Together with kinetic analyses using a library of amino acid substrates, our mutagenesis and structural studies allow us to propose a binding model that explains the dual l/d specificity of DPAT. Our kinetic analyses also demonstrate that DPAT can catalyze the transamination of β- and γ-amino acids, reclassifying this enzyme as an ω-aminotransferase. Collectively, our studies highlight that the DPAT active site is amenable to protein engineering for expansion of its substrate scope, which offers the opportunity to generate new biocatalysts for the synthesis of a variety of valuable optically pure d-amino acids from inexpensive and abundant l-amino acids.
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Affiliation(s)
- Curtis J W Walton
- Department of Chemistry and Biomolecular Sciences , University of Ottawa , Ottawa , Ontario , Canada K1N 6N5.,Centre for Catalysis Research and Innovation , University of Ottawa , Ottawa , Ontario , Canada K1N 6N5
| | - Frédéric Thiebaut
- Department of Chemistry and Biomolecular Sciences , University of Ottawa , Ottawa , Ontario , Canada K1N 6N5.,Centre for Catalysis Research and Innovation , University of Ottawa , Ottawa , Ontario , Canada K1N 6N5
| | - Joseph S Brunzelle
- Life Science Collaborative Access Team, Northwestern Synchrotron Research Centers , Northwestern University , Argonne , Illinois 60439 , United States
| | - Jean-François Couture
- Centre for Catalysis Research and Innovation , University of Ottawa , Ottawa , Ontario , Canada K1N 6N5.,Department of Biochemistry, Microbiology and Immunology, and Ottawa Institute of Systems Biology , University of Ottawa , Ottawa , Ontario , Canada K1H 8M5
| | - Roberto A Chica
- Department of Chemistry and Biomolecular Sciences , University of Ottawa , Ottawa , Ontario , Canada K1N 6N5.,Centre for Catalysis Research and Innovation , University of Ottawa , Ottawa , Ontario , Canada K1N 6N5
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A kinetic spectrophotometric method for the determination of pyridoxal-5'-phosphate based on coenzyme activation of apo-d-phenylglycine aminotransferase. Enzyme Microb Technol 2018; 117:64-71. [PMID: 30037553 DOI: 10.1016/j.enzmictec.2018.06.003] [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: 03/21/2018] [Revised: 06/12/2018] [Accepted: 06/13/2018] [Indexed: 11/21/2022]
Abstract
A new PLP assay method based on the coenzyme activation of apo-d-phenylglycine aminotransferase (apo-d-PhgAT) is reported. The assay process is comprised of two steps. First, PLP present in plasma samples is allowed to reconstitute apo-d-PhgAT, forming active holo-d-PhgAT. In the second step, the enzymatic activity of reconstituted d-PhgAT is determined using d-4-OH-phenylglycine as the amino donor substrate with 4-OH-benzoylformate (OH-BZF) as the reaction product. OH-BZF absorbs UV light strongly at 334 nm (molar absorption coefficient = 25.4 × 103 M-1cm-1) and its rate of formation is monitored spectrophotometrically. The rate of the transamination reaction catalyzed by the reconstituted d-PhgAT is directly proportional to the amount of PLP in the sample. The method is applicable for determining PLP in the concentration range from 5.2 to 250 nM and requires 50 μL of plasma sample. The mean within- and between-run coefficient of variations (CVs) were 8.1% and 12.4%, respectively. Analytical recoveries ranged from 98 to 108%. The assay was specific and showed good correlation with the established method (CDC, Method No: 4002.05). The assay requires one reaction catalyzed by a single enzyme, does not require a radioactive substrate, and a derivatization reagent is not needed. This PLP determination process is relatively simple to perform and can be completed using common laboratory equipment.
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Use of nonionic surfactants for improvement of terpene production in Saccharomyces cerevisiae. Appl Environ Microbiol 2014; 80:6685-93. [PMID: 25149518 DOI: 10.1128/aem.02155-14] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022] Open
Abstract
To facilitate enzyme and pathway engineering, a selection was developed for improved sesquiterpene titers in Saccharomyces cerevisiae. α-Bisabolene, a candidate advanced biofuel, was found to protect yeast against the disruptive action of nonionic surfactants such as Tween 20 (T20). An experiment employing competition between two strains of yeast, one of which makes twice as much bisabolene as the other, demonstrated that growth in the presence of T20 provided sufficient selective pressure to enrich the high-titer strain to form 97% of the population. Following this, various methods were used to mutagenize the bisabolene synthase (BIS) coding sequence, coupled with selection by subculturing in the presence of T20. Mutagenesis targeting the BIS active site did not yield an improvement in bisabolene titers, although mutants were found which made a mixture of α-bisabolene and β-farnesene, another candidate biofuel. Based on evidence that the 3' end of the BIS mRNA may be unstable in yeast, we randomly recoded the last 20 amino acids of the enzyme and, following selection in T20, found a variant which increased specific production of bisabolene by more than 30%. Since T20 could enrich a mixed population, efficiently removing strains that produced little or no bisabolene, we investigated whether it could also be applied to sustain high product titers in a monoculture for an extended period. Cultures grown in the presence of T20 for 14 days produced bisabolene at titers up to 4-fold higher than cultures grown with an overlay of dodecane, used to sequester the terpene product, and 20-fold higher than cultures grown without dodecane.
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