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Meeks KR, Ji J, Protopopov MV, Tarkhanova OO, Moroz YS, Tanner JJ. Novel Fragment Inhibitors of PYCR1 from Docking-Guided X-ray Crystallography. J Chem Inf Model 2024; 64:1704-1718. [PMID: 38411104 PMCID: PMC11058006 DOI: 10.1021/acs.jcim.3c01879] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/28/2024]
Abstract
The proline biosynthetic enzyme Δ1-pyrroline-5-carboxylate (P5C) reductase 1 (PYCR1) is one of the most consistently upregulated enzymes across multiple cancer types and central to the metabolic rewiring of cancer cells. Herein, we describe a fragment-based, structure-first approach to the discovery of PYCR1 inhibitors. Thirty-seven fragment-like carboxylic acids in the molecular weight range of 143-289 Da were selected from docking and then screened using X-ray crystallography as the primary assay. Strong electron density was observed for eight compounds, corresponding to a crystallographic hit rate of 22%. The fragments are novel compared to existing proline analog inhibitors in that they block both the P5C substrate pocket and the NAD(P)H binding site. Four hits showed inhibition of PYCR1 in kinetic assays, and one has lower apparent IC50 than the current best proline analog inhibitor. These results show proof-of-concept for our inhibitor discovery approach and provide a basis for fragment-to-lead optimization.
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Affiliation(s)
- Kaylen R Meeks
- Department of Biochemistry, University of Missouri, Columbia, Missouri 65211, United States
| | - Juan Ji
- Department of Biochemistry, University of Missouri, Columbia, Missouri 65211, United States
| | | | - Olga O Tarkhanova
- Chemspace LLC, 85 Chervonotkatska Street, Suite 1, Kyïv 02094, Ukraine
| | - Yurii S Moroz
- Chemspace LLC, 85 Chervonotkatska Street, Suite 1, Kyïv 02094, Ukraine
- Department of Chemistry, Taras Shevchenko National University of Kyïv, Kyïv 01601, Ukraine
| | - John J Tanner
- Department of Biochemistry, University of Missouri, Columbia, Missouri 65211, United States
- Department of Chemistry, University of Missouri, Columbia, Missouri 65211, United States
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2
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Bogner AN, Ji J, Tanner JJ. Structure-based engineering of minimal proline dehydrogenase domains for inhibitor discovery. Protein Eng Des Sel 2022; 35:gzac016. [PMID: 36448708 PMCID: PMC9801229 DOI: 10.1093/protein/gzac016] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/23/2022] [Revised: 11/11/2022] [Accepted: 11/21/2022] [Indexed: 12/03/2022] Open
Abstract
Proline dehydrogenase (PRODH) catalyzes the FAD-dependent oxidation of l-proline to Δ1-pyrroline-5-carboxylate and is a target for inhibitor discovery because of its importance in cancer cell metabolism. Because human PRODH is challenging to purify, the PRODH domains of the bacterial bifunctional enzyme proline utilization A (PutA) have been used for inhibitor development. These systems have limitations due to large polypeptide chain length, conformational flexibility and the presence of domains unrelated to PRODH activity. Herein, we report the engineering of minimal PRODH domains for inhibitor discovery. The best designs contain one-third of the 1233-residue PutA from Sinorhizobium meliloti and include a linker that replaces the PutA α-domain. The minimal PRODHs exhibit near wild-type enzymatic activity and are susceptible to known inhibitors and inactivators. Crystal structures of minimal PRODHs inhibited by S-(-)-tetrahydro-2-furoic acid and 2-(furan-2-yl)acetic acid were determined at 1.23 and 1.72 Å resolution. Minimal PRODHs should be useful in chemical probe discovery.
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Affiliation(s)
- Alexandra N Bogner
- Department of Biochemistry, University of Missouri, Columbia, MO 65211, USA
| | - Juan Ji
- Department of Biochemistry, University of Missouri, Columbia, MO 65211, USA
| | - John J Tanner
- Department of Biochemistry, University of Missouri, Columbia, MO 65211, USA
- Department of Chemistry, University of Missouri, Columbia, MO 65211, USA
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3
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Bogner AN, Tanner JJ. Structure-affinity relationships of reversible proline analog inhibitors targeting proline dehydrogenase. Org Biomol Chem 2022; 20:895-905. [PMID: 35018940 PMCID: PMC8864676 DOI: 10.1039/d1ob02328d] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Abstract
Proline dehydrogenase (PRODH) catalyzes the first step of proline catabolism, the FAD-dependent oxidation of L-proline to Δ1-pyrroline-5-carboxylate. PRODH plays a central role in the metabolic rewiring of cancer cells, which has motivated the discovery of inhibitors. Here, we studied the inhibition of PRODH by 18 proline-like compounds to understand the structural and chemical features responsible for the affinity of the best-known inhibitor, S-(-)-tetrahydro-2-furoic acid (1). The compounds were screened, and then six were selected for more thorough kinetic analysis: cyclobutane-1,1-dicarboxylic acid (2), cyclobutanecarboxylic acid (3), cyclopropanecarboxylic acid (4), cyclopentanecarboxylic acid (16), 2-oxobutyric acid (17), and (2S)-oxetane-2-carboxylic acid (18). These compounds are competitive inhibitors with inhibition constants in the range of 1.4-6 mM, compared to 0.3 mM for 1. Crystal structures of PRODH complexed with 2, 3, 4, and 18 were determined. All four inhibitors bind in the proline substrate site, but the orientations of their rings differ from that of 1. The binding of 3 and 18 is accompanied by compression of the active site to enable nonpolar contacts with Leu513. Compound 2 is unique in that the additional carboxylate displaces a structurally conserved water molecule from the active site. Compound 18 also destabilizes the conserved water, but by an unexpected non-steric mechanism. The results are interpreted using a chemical double mutant thermodynamic cycle. This analysis revealed unanticipated synergism between ring size and hydrogen bonding to the conserved water. These structure-affinity relationships provide new information relevant to the development of new inhibitor design strategies targeting PRODH.
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Affiliation(s)
- Alexandra N. Bogner
- Department of Biochemistry, University of Missouri, Columbia, Missouri 65211, United States
| | - John J. Tanner
- Department of Biochemistry, University of Missouri, Columbia, Missouri 65211, United States.,Department of Chemistry, University of Missouri, Columbia, Missouri 65211, United States
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4
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Iyer A, Reis RAG, Agniswamy J, Weber IT, Gadda G. Discovery of a new flavin N5-adduct in a tyrosine to phenylalanine variant of d-Arginine dehydrogenase. Arch Biochem Biophys 2022; 715:109100. [PMID: 34864048 DOI: 10.1016/j.abb.2021.109100] [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: 10/29/2021] [Revised: 11/29/2021] [Accepted: 11/30/2021] [Indexed: 11/02/2022]
Abstract
d-Arginine dehydrogenase from Pseudomonas aeruginosa (PaDADH) catalyzes the flavin-dependent oxidation of d-arginine and other d-amino acids. Here, we report the crystal structure at 1.29 Å resolution for PaDADH-Y249F expressed and co-crystallized with d-arginine. The overall structure of PaDADH-Y249F resembled PaDADH-WT, but the electron density for the flavin cofactor was ambiguous, suggesting the presence of modified flavins. Electron density maps and mass spectrometric analysis confirmed the presence of both N5-(4-guanidino-oxobutyl)-FAD and 6-OH-FAD in a single crystal of PaDADH-Y249F and helped with the further refinement of the X-ray crystal structure. The versatility of the reduced flavin is apparent in the PaDADH-Y249F structure and is evidenced by the multiple functions it can perform in the same active site.
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Affiliation(s)
- Archana Iyer
- Department of Chemistry, Georgia State University, Atlanta, GA, 30302, USA
| | - Renata A G Reis
- Department of Chemistry, Georgia State University, Atlanta, GA, 30302, USA
| | - Johnson Agniswamy
- Department of Biology, Georgia State University, Atlanta, GA, 30302, USA
| | - Irene T Weber
- Department of Chemistry, Georgia State University, Atlanta, GA, 30302, USA; Department of Biology, Georgia State University, Atlanta, GA, 30302, USA
| | - Giovanni Gadda
- Department of Chemistry, Georgia State University, Atlanta, GA, 30302, USA; Department of Biology, Georgia State University, Atlanta, GA, 30302, USA; Center for Diagnostics and Therapeutics, Georgia State University, Atlanta, GA, 30302, USA.
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5
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Scott GK, Mahoney S, Scott M, Loureiro A, Lopez-Ramirez A, Tanner JJ, Ellerby LM, Benz CC. N-Propargylglycine: a unique suicide inhibitor of proline dehydrogenase with anticancer activity and brain-enhancing mitohormesis properties. Amino Acids 2021; 53:1927-1939. [PMID: 34089390 PMCID: PMC8643368 DOI: 10.1007/s00726-021-03012-9] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/04/2020] [Accepted: 05/28/2021] [Indexed: 12/03/2022]
Abstract
Proline dehydrogenase (PRODH) is a mitochondrial inner membrane flavoprotein critical for cancer cell survival under stress conditions and newly recognized as a potential target for cancer drug development. Reversible (competitive) and irreversible (suicide) inhibitors of PRODH have been shown in vivo to inhibit cancer cell growth with excellent host tolerance. Surprisingly, the PRODH suicide inhibitor N-propargylglycine (N-PPG) also induces rapid decay of PRODH with concordant upregulation of mitochondrial chaperones (HSP-60, GRP-75) and the inner membrane protease YME1L1, signifying activation of the mitochondrial unfolded protein response (UPRmt) independent of anticancer activity. The present study was undertaken to address two aims: (i) use PRODH overexpressing human cancer cells (ZR-75-1) to confirm the UPRmt inducing properties of N-PPG relative to another equipotent irreversible PRODH inhibitor, thiazolidine-2-carboxylate (T2C); and (ii) employ biochemical and transcriptomic approaches to determine if orally administered N-PPG can penetrate the blood-brain barrier, essential for its future use as a brain cancer therapeutic, and also potentially protect normal brain tissue by inducing mitohormesis. Oral daily treatments of N-PPG produced a dose-dependent decline in brain mitochondrial PRODH protein without detectable impairment in mouse health; furthermore, mice repeatedly dosed with 50 mg/kg N-PPG showed increased brain expression of the mitohormesis associated protease, YME1L1. Whole brain transcriptome (RNAseq) analyses of these mice revealed significant gene set enrichment in N-PPG stimulated neural processes (FDR p < 0.05). Given this in vivo evidence of brain bioavailability and neural mitohormesis induction, N-PPG appears to be unique among anticancer agents and should be evaluated for repurposing as a pharmaceutical capable of mitigating the proteotoxic mechanisms driving neurodegenerative disorders.
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Affiliation(s)
- Gary K Scott
- Buck Institute for Research on Aging, 8001 Redwood Blvd., Novato, CA, 94945, USA
| | - Sophia Mahoney
- Buck Institute for Research on Aging, 8001 Redwood Blvd., Novato, CA, 94945, USA
| | - Madeleine Scott
- Department of Medicine, Center for Biomedical Informatics, Stanford University School of Medicine, Stanford, CA, 94305, USA
| | - Ashley Loureiro
- Buck Institute for Research on Aging, 8001 Redwood Blvd., Novato, CA, 94945, USA
| | | | - John J Tanner
- Department of Biochemistry, University of Missouri, Columbia, MO, 65211, USA
| | - Lisa M Ellerby
- Buck Institute for Research on Aging, 8001 Redwood Blvd., Novato, CA, 94945, USA
| | - Christopher C Benz
- Buck Institute for Research on Aging, 8001 Redwood Blvd., Novato, CA, 94945, USA.
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6
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Mao Y, Seravalli J, Smith TG, Morton M, Tanner JJ, Becker DF. Evidence for Proline Catabolic Enzymes in the Metabolism of Thiazolidine Carboxylates. Biochemistry 2021; 60:3610-3620. [PMID: 34752700 DOI: 10.1021/acs.biochem.1c00625] [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
Thiazolidine carboxylates such as thiazolidine-4-carboxylate (T4C) and thiazolidine-2-carboxylate (T2C) are naturally occurring sulfur analogues of proline. These compounds have been observed to have both beneficial and toxic effects in cells. Given that proline dehydrogenase has been proposed to be a key enzyme in the oxidative metabolism of thioprolines, we characterized T4C and T2C as substrates of proline catabolic enzymes using proline utilization A (PutA), which is a bifunctional enzyme with proline dehydrogenase (PRODH) and l-glutamate-γ-semialdehyde dehydrogenase (GSALDH) activities. PutA is shown here to catalyze the FAD-dependent PRODH oxidation of both T4C and T2C with catalytic efficiencies significantly higher than with proline. Stopped-flow experiments also demonstrate that l-T4C and l-T2C reduce PutA-bound FAD at rates faster than proline. Unlike proline, however, oxidation of T4C and T2C does not generate a substrate for NAD+-dependent GSALDH. Instead, PutA/PRODH oxidation of T4C leads to cysteine formation, whereas oxidation of T2C generates an apparently stable Δ4-thiazoline-2-carboxylate species. Our results provide new insights into the metabolism of T2C and T4C.
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Affiliation(s)
- Yizi Mao
- Department of Biochemistry, Redox Biology Center, University of Nebraska, Lincoln, Nebraska 68588, United States
| | - Javier Seravalli
- Department of Biochemistry, Redox Biology Center, University of Nebraska, Lincoln, Nebraska 68588, United States
| | - Thomas G Smith
- Department of Chemistry, University of Nebraska, Lincoln, Nebraska 68588, United States
| | - Martha Morton
- Department of Chemistry, University of Nebraska, Lincoln, Nebraska 68588, United States
| | - John J Tanner
- Departments of Biochemistry and Chemistry, University of Missouri, Columbia, Missouri 65211, United States
| | - Donald F Becker
- Department of Biochemistry, Redox Biology Center, University of Nebraska, Lincoln, Nebraska 68588, United States
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7
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Campbell AC, Prater AR, Bogner AN, Quinn TP, Gates KS, Becker DF, Tanner JJ. Photoinduced Covalent Irreversible Inactivation of Proline Dehydrogenase by S-Heterocycles. ACS Chem Biol 2021; 16:2268-2279. [PMID: 34542291 DOI: 10.1021/acschembio.1c00427] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023]
Abstract
Proline dehydrogenase (PRODH) is a flavoenzyme that catalyzes the first step of proline catabolism, the oxidation of l-proline to Δ1-pyrroline-5-carboxylate. PRODH has emerged as a cancer therapy target because of its involvement in the metabolic reprogramming of cancer cells. Here, we report the discovery of a new class of PRODH inactivator, which covalently and irreversibly modifies the FAD in a light-dependent manner. Two examples, 1,3-dithiolane-2-carboxylate and tetrahydrothiophene-2-carboxylate, have been characterized using X-ray crystallography (1.52-1.85 Å resolution), absorbance spectroscopy, and enzyme kinetics. The structures reveal that in the dark, these compounds function as classical reversible, proline analogue inhibitors. However, exposure of enzyme-inhibitor cocrystals to bright white light induces decarboxylation of the inhibitor and covalent attachment of the residual S-heterocycle to the FAD N5 atom, locking the cofactor into a reduced, inactive state. Spectroscopic measurements of the inactivation process in solution confirm the requirement for light and show that blue light is preferred. Enzyme activity assays show that the rate of inactivation is enhanced by light and that the inactivation is irreversible. We also demonstrate the photosensitivity of cancer cells to one of these compounds. A possible mechanism is proposed involving photoexcitation of the FAD, while the inhibitor is noncovalently bound in the active site, followed by electron transfer, decarboxylation, and radical combination steps. Our results could lead to the development of photopharmacological drugs targeting PRODH.
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Affiliation(s)
- Ashley C. Campbell
- Department of Biochemistry, University of Missouri, Columbia, Missouri 65211, United States
| | - Austin R. Prater
- Department of Biochemistry, University of Missouri, Columbia, Missouri 65211, United States
| | - Alexandra N. Bogner
- Department of Biochemistry, University of Missouri, Columbia, Missouri 65211, United States
| | - Thomas P. Quinn
- Department of Biochemistry, University of Missouri, Columbia, Missouri 65211, United States
| | - Kent S. Gates
- Department of Chemistry, University of Missouri, Columbia, Missouri 65211, United States
| | - Donald F. Becker
- Department of Biochemistry, Redox Biology Center, University of Nebraska, Lincoln, Nebraska 68588, United States
| | - John J. Tanner
- Department of Biochemistry, University of Missouri, Columbia, Missouri 65211, United States
- Department of Chemistry, University of Missouri, Columbia, Missouri 65211, United States
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8
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Christensen EM, Bogner AN, Vandekeere A, Tam GS, Patel SM, Becker DF, Fendt SM, Tanner JJ. In crystallo screening for proline analog inhibitors of the proline cycle enzyme PYCR1. J Biol Chem 2020; 295:18316-18327. [PMID: 33109600 PMCID: PMC7939384 DOI: 10.1074/jbc.ra120.016106] [Citation(s) in RCA: 21] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/18/2020] [Revised: 10/22/2020] [Indexed: 12/20/2022] Open
Abstract
Pyrroline-5-carboxylate reductase 1 (PYCR1) catalyzes the biosynthetic half-reaction of the proline cycle by reducing Δ1-pyrroline-5-carboxylate (P5C) to proline through the oxidation of NAD(P)H. Many cancers alter their proline metabolism by up-regulating the proline cycle and proline biosynthesis, and knockdowns of PYCR1 lead to decreased cell proliferation. Thus, evidence is growing for PYCR1 as a potential cancer therapy target. Inhibitors of cancer targets are useful as chemical probes for studying cancer mechanisms and starting compounds for drug discovery; however, there is a notable lack of validated inhibitors for PYCR1. To fill this gap, we performed a small-scale focused screen of proline analogs using X-ray crystallography. Five inhibitors of human PYCR1 were discovered: l-tetrahydro-2-furoic acid, cyclopentanecarboxylate, l-thiazolidine-4-carboxylate, l-thiazolidine-2-carboxylate, and N-formyl l-proline (NFLP). The most potent inhibitor was NFLP, which had a competitive (with P5C) inhibition constant of 100 μm The structure of PYCR1 complexed with NFLP shows that inhibitor binding is accompanied by conformational changes in the active site, including the translation of an α-helix by 1 Å. These changes are unique to NFLP and enable additional hydrogen bonds with the enzyme. NFLP was also shown to phenocopy the PYCR1 knockdown in MCF10A H-RASV12 breast cancer cells by inhibiting de novo proline biosynthesis and impairing spheroidal growth. In summary, we generated the first validated chemical probe of PYCR1 and demonstrated proof-of-concept for screening proline analogs to discover inhibitors of the proline cycle.
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Affiliation(s)
| | - Alexandra N Bogner
- Department of Biochemistry, University of Missouri, Columbia, Missouri, USA
| | - Anke Vandekeere
- Laboratory of Cellular Metabolism and Metabolic Regulation, VIB-KU Leuven Center for Cancer Biology, VIB, Leuven, Belgium; Department of Oncology, Laboratory of Cellular Metabolism and Metabolic Regulation, KU Leuven and Leuven Cancer Institute (LKI), Leuven, Belgium
| | - Gabriela S Tam
- Department of Biochemistry, University of Missouri, Columbia, Missouri, USA
| | - Sagar M Patel
- Department of Biochemistry, Redox Biology Center, University of Nebraska, Lincoln, Nebraska, USA
| | - Donald F Becker
- Department of Biochemistry, Redox Biology Center, University of Nebraska, Lincoln, Nebraska, USA
| | - Sarah-Maria Fendt
- Laboratory of Cellular Metabolism and Metabolic Regulation, VIB-KU Leuven Center for Cancer Biology, VIB, Leuven, Belgium; Department of Oncology, Laboratory of Cellular Metabolism and Metabolic Regulation, KU Leuven and Leuven Cancer Institute (LKI), Leuven, Belgium
| | - John J Tanner
- Department of Biochemistry, University of Missouri, Columbia, Missouri, USA; Department of Chemistry, University of Missouri, Columbia, Missouri, USA.
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9
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Campbell AC, Bogner AN, Mao Y, Becker DF, Tanner JJ. Structural analysis of prolines and hydroxyprolines binding to the l-glutamate-γ-semialdehyde dehydrogenase active site of bifunctional proline utilization A. Arch Biochem Biophys 2020; 698:108727. [PMID: 33333077 DOI: 10.1016/j.abb.2020.108727] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/19/2020] [Revised: 12/11/2020] [Accepted: 12/12/2020] [Indexed: 01/31/2023]
Abstract
Proline utilization A (PutA) proteins are bifunctional proline catabolic enzymes that catalyze the 4-electron oxidation of l-proline to l-glutamate using spatially-separated proline dehydrogenase and l-glutamate-γ-semialdehyde dehydrogenase (GSALDH, a.k.a. ALDH4A1) active sites. The observation that l-proline inhibits both the GSALDH activity of PutA and monofunctional GSALDHs motivated us to study the inhibition of PutA by proline stereoisomers and analogs. Here we report five high-resolution crystal structures of PutA with the following ligands bound in the GSALDH active site: d-proline, trans-4-hydroxy-d-proline, cis-4-hydroxy-d-proline, l-proline, and trans-4-hydroxy-l-proline. Three of the structures are of ternary complexes of the enzyme with an inhibitor and either NAD+ or NADH. To our knowledge, the NADH complex is the first for any GSALDH. The structures reveal a conserved mode of recognition of the inhibitor carboxylate, which results in the pyrrolidine rings of the d- and l-isomers having different orientations and different hydrogen bonding environments. Activity assays show that the compounds are weak inhibitors with millimolar inhibition constants. Curiously, although the inhibitors occupy the aldehyde binding site, kinetic measurements show the inhibition is uncompetitive. Uncompetitive inhibition may involve proline binding to a remote site or to the enzyme-NADH complex. Together, the structural and kinetic data expand our understanding of how proline-like molecules interact with GSALDH, reveal insight into the relationship between stereochemistry and inhibitor affinity, and demonstrate the pitfalls of inferring the mechanism of inhibition from crystal structures alone.
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Affiliation(s)
- Ashley C Campbell
- Department of Biochemistry, University of Missouri, Columbia, MO, 65211, United States
| | - Alexandra N Bogner
- Department of Biochemistry, University of Missouri, Columbia, MO, 65211, United States
| | - Yizi Mao
- Department of Biochemistry, Redox Biology Center, University of Nebraska, Lincoln, NE, 68588, United States
| | - Donald F Becker
- Department of Biochemistry, Redox Biology Center, University of Nebraska, Lincoln, NE, 68588, United States
| | - John J Tanner
- Department of Biochemistry, University of Missouri, Columbia, MO, 65211, United States; Department of Chemistry, University of Missouri, Columbia, MO, 65211, United States.
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