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Panigrahi K, Fei X, Kitamura M, Berkowitz DB. Rapid Entry into Biologically Relevant α,α-Difluoroalkylphosphonates Bearing Allyl Protection-Deblocking under Ru(II)/(IV)-Catalysis. Org Lett 2019; 21:9846-9851. [PMID: 31789041 DOI: 10.1021/acs.orglett.9b03707] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
A convenient synthetic route to α,α-difluoroalkylphosphonates is described. Structurally diverse aldehydes are condensed with LiF2CP(O)(OCH2CH═CH2)2. The resultant alcohols are captured as the pentafluorophenyl thionocarbonates and efficiently deoxygenated with HSnBu3, BEt3, and O2, and then smoothly deblocked with CpRu(IV)(π-allyl)quinoline-2-carboxylate (1-2 mol %) in methanol as an allyl cation scavenger. These mild deprotection conditions provide access to free α,α-difluoroalkylphosphonates in nearly quantitative yield. This methodology is used to rapidly construct new bis-α,α-difluoroalkyl phosphonate inhibitors of PTPIB (protein phosphotyrosine phosphatase-1B).
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Affiliation(s)
- Kaushik Panigrahi
- Department of Chemistry , University of Nebraska , Lincoln , Nebraska 68588-0304 , United States
| | - Xiang Fei
- Department of Chemistry , University of Nebraska , Lincoln , Nebraska 68588-0304 , United States
| | - Masato Kitamura
- Graduate School of Pharmaceutical Sciences , Nagoya University , Furo-cho, Chikusa-ku, Nagoya 464-8602 , Japan
| | - David B Berkowitz
- Department of Chemistry , University of Nebraska , Lincoln , Nebraska 68588-0304 , United States
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2
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Peng Y, Zhang X, Qi X, He Q, Zhang B, Hao J, Yang C. Metal-Free Access to (E/Z
)-α-Fluorovinyl Phosphorus Compounds from gem
-Difluorostyrenes. European J Org Chem 2019. [DOI: 10.1002/ejoc.201801602] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Affiliation(s)
- Yingyuan Peng
- Department of Chemistry; Innovative Drug Research Center; Shanghai University; Shangda Road 99 200436 Shanghai China
| | - Xiaofei Zhang
- State Key Laboratory of Drug Research; Shanghai Institute of Materia Medica; Chinese Academy of Sciences; 555 Zu Chong Zhi Road 201203 Shanghai China
| | - Xueyu Qi
- State Key Laboratory of Drug Research; Shanghai Institute of Materia Medica; Chinese Academy of Sciences; 555 Zu Chong Zhi Road 201203 Shanghai China
| | - Qian He
- State Key Laboratory of Drug Research; Shanghai Institute of Materia Medica; Chinese Academy of Sciences; 555 Zu Chong Zhi Road 201203 Shanghai China
| | - Bin Zhang
- Department of Chemistry; Innovative Drug Research Center; Shanghai University; Shangda Road 99 200436 Shanghai China
| | - Jian Hao
- Department of Chemistry; Innovative Drug Research Center; Shanghai University; Shangda Road 99 200436 Shanghai China
| | - Chunhao Yang
- State Key Laboratory of Drug Research; Shanghai Institute of Materia Medica; Chinese Academy of Sciences; 555 Zu Chong Zhi Road 201203 Shanghai China
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3
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Rossignoli G, Phillips RS, Astegno A, Menegazzi M, Voltattorni CB, Bertoldi M. Phosphorylation of pyridoxal 5'-phosphate enzymes: an intriguing and neglected topic. Amino Acids 2017; 50:205-215. [PMID: 29204749 DOI: 10.1007/s00726-017-2521-3] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/16/2017] [Accepted: 11/29/2017] [Indexed: 12/25/2022]
Abstract
Pyridoxal 5'-phosphate (PLP)-dependent enzymes catalyze a wide range of reactions of amino acids and amines, with the exception of glycogen phosphorylase which exhibits peculiar both substrate preference and chemical mechanism. They represent about 4% of the gene products in eukaryotic cells. Although structure-function investigations regarding these enzymes are copious, their regulation by post-translational modifications is largely unknown. Protein phosphorylation is the most common post-translational modification fundamental in mediating diverse cellular functions. This review aims at summarizing the current knowledge on regulation of PLP enzymes by phosphorylation. Starting from the paradigmatic PLP-dependent glycogen phosphorylase, the first phosphoprotein discovered, we collect data in literature regarding functional phosphorylation events of eleven PLP enzymes belonging to different fold types and discuss the impact of the modification in affecting their activity and localization as well as the implications on the pathogenesis of diseases in which many of these enzymes are involved. The pivotal question is to correlate the structural consequences of phosphorylation among PLP enzymes of different folds with the functional modifications exerted in terms of activity or conformational changes or others. Although the literature shows that the phosphorylation of PLP enzymes plays important roles in mediating diverse cellular functions, our recapitulation of clue findings in the field makes clear that there is still much to be learnt. Besides mass spectrometry-based proteomic analyses, further biochemical and structural studies on purified native proteins are imperative to fully understand and predict how phosphorylation regulates PLP enzymes and to find the relationship between addition of a phosphate moiety and physiological response.
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Affiliation(s)
- Giada Rossignoli
- Department of Neuroscience, Biomedicine and Movement, University of Verona, Strada Le Grazie, 8, 37134, Verona, Italy
| | - Robert S Phillips
- Department of Chemistry, University of Georgia, Athens, GA, 30602, USA.,Department of Biochemistry and Molecular Biology, University of Georgia, Athens, GA, 30602, USA
| | - Alessandra Astegno
- Department of Biotechnology, University of Verona, Strada Le Grazie, 15, 37134, Verona, Italy
| | - Marta Menegazzi
- Department of Neuroscience, Biomedicine and Movement, University of Verona, Strada Le Grazie, 8, 37134, Verona, Italy
| | - Carla Borri Voltattorni
- Department of Neuroscience, Biomedicine and Movement, University of Verona, Strada Le Grazie, 8, 37134, Verona, Italy
| | - Mariarita Bertoldi
- Department of Neuroscience, Biomedicine and Movement, University of Verona, Strada Le Grazie, 8, 37134, Verona, Italy.
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4
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Phillips RS, Scott I, Paulose R, Patel A, Barron TC. The phosphate of pyridoxal-5'-phosphate is an acid/base catalyst in the mechanism of Pseudomonas fluorescens kynureninase. FEBS J 2014; 281:1100-9. [PMID: 24304904 DOI: 10.1111/febs.12671] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/18/2013] [Revised: 11/27/2013] [Accepted: 12/02/2013] [Indexed: 11/28/2022]
Abstract
Kynureninase (L-kynurenine hydrolase, EC 3.7.1.3) catalyzes the hydrolytic cleavage of L-kynurenine to L-alanine and anthranilic acid. The proposed mechanism of the retro-Claisen reaction requires extensive acid/base catalysis. Previous crystal structures showed that Tyr226 in the Pseudomonas fluorescens enzyme (Tyr275 in the human enzyme) hydrogen bonds to the phosphate of the pyridoxal-5'-phosphate (PLP) cofactor. This Tyr residue is strictly conserved in all sequences of kynureninase. The human enzyme complexed with a competitive inhibitor, 3-hydroxyhippuric acid, showed that the ligand carbonyl O is located 3.7 Å from the phenol of Tyr275 (Lima, S., Kumar, S., Gawandi, V., Momany, C. & Phillips, R. S. (2009) J. Med. Chem. 52, 389-396). We prepared a Y226F mutant of P. fluorescens kynureninase to probe the role of this residue in catalysis. The Y226F mutant has approximately 3000-fold lower activity than wild-type, and does not show the pKa values of 6.8 on kcat and 6.5 and 8.8 on k(cat)/K(m) seen for the wild-type enzyme (Koushik, S. V., Moore, J. A. III, Sundararaju, B. & Phillips, R. S. (1998) Biochemistry 37, 1376-1382). Wild-type kynureninase shows a resonance at 4.5 ppm in (31)P-NMR, which is shifted to 5.0, 3.3 and 2.0 ppm when the potent inhibitor 5-bromodihydrokynurenine is added. However, Y226F kynureninase shows resonances at 3.6 and 2.5 ppm, and no change in the peak position is seen when 5-bromodihydrokynurenine is added. Taken together, these results suggest that Tyr226 mediates proton transfer between the substrate and the phosphate, which accelerates formation of external aldimine and gem-diol intermediates. Thus, the phosphate of PLP acts as an acid/base catalyst in the mechanism of kynureninase.
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Affiliation(s)
- Robert S Phillips
- Department of Biochemistry and Molecular Biology, University Georgia, Athens, GA, USA; Department of Chemistry, University Georgia, Athens, GA, USA
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5
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Bollinger M, Manzenrieder F, Kolb R, Bochen A, Neubauer S, Marinelli L, Limongelli V, Novellino E, Moessmer G, Pell R, Lindner W, Fanous J, Hoffman A, Kessler H. Tailoring of integrin ligands: probing the charge capability of the metal ion-dependent adhesion site. J Med Chem 2012; 55:871-82. [PMID: 22185640 DOI: 10.1021/jm2013826] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
Abstract
Intervention in integrin-mediated cell adhesion and integrin signaling pathways is an ongoing area of research in medicinal chemistry and drug development. One key element in integrin-ligand interaction is the coordination of the bivalent cation at the metal ion-dependent adhesion site (MIDAS) by a carboxylic acid function, a consistent feature of all integrin ligands. With the exception of the recently discovered hydroxamic acids, all bioisosteric attempts to replace the carboxylic acid of integrin ligands failed. We report that phosphinates as well as monomethyl phosphonates represent excellent isosters, when introduced into integrin antagonists for the platelet integrin αIIbβ3. The novel inhibitors exhibit in vitro and ex vivo activities in the low nanomolar range. Steric and charge requirements of the MIDAS region were unraveled, thus paving the way for an in silico prediction of ligand activity and in turn the rational design of the next generation of integrin antagonists.
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Affiliation(s)
- Markus Bollinger
- Institute for Advanced Study and Center of Integrated Protein Science, Department Chemie, Technische Universität München, Lichtenbergstrasse 4, 85747 Garching, Germany
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6
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Talukdar A, Morgunova E, Duan J, Meining W, Foloppe N, Nilsson L, Bacher A, Illarionov B, Fischer M, Ladenstein R, Cushman M. Virtual screening, selection and development of a benzindolone structural scaffold for inhibition of lumazine synthase. Bioorg Med Chem 2010; 18:3518-34. [PMID: 20430628 PMCID: PMC2868945 DOI: 10.1016/j.bmc.2010.03.072] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/08/2010] [Revised: 03/24/2010] [Accepted: 03/25/2010] [Indexed: 10/19/2022]
Abstract
Virtual screening of a library of commercially available compounds versus the structure of Mycobacterium tuberculosis lumazine synthase identified 2-(2-oxo-1,2-dihydrobenzo[cd]indole-6-sulfonamido)acetic acid (9) as a possible lead compound. Compound 9 proved to be an effective inhibitor of M. tuberculosis lumazine synthase with a K(i) of 70microM. Lead optimization through replacement of the carboxymethylsulfonamide sidechain with sulfonamides substituted with alkyl phosphates led to a four-carbon phosphate 38 that displayed a moderate increase in enzyme inhibitory activity (K(i) 38microM). Molecular modeling based on known lumazine synthase/inhibitor crystal structures suggests that the main forces stabilizing the present benzindolone/enzyme complexes involve pi-pi stacking interactions with Trp27 and hydrogen bonding of the phosphates with Arg128, the backbone nitrogens of Gly85 and Gln86, and the side chain hydroxyl of Thr87.
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Affiliation(s)
- Arindam Talukdar
- Department of Medicinal Chemistry and Molecular Pharmacology, School of Pharmacy and Pharmaceutical Sciences, and The Purdue Center for Cancer Research, Purdue University, West Lafayette, Indiana, 47907, USA
| | - Ekaterina Morgunova
- Karolinska Institute, Department of Bioscience, Hälsovägen 7-9, S-14157 Huddinge, Sweden
| | - Jianxin Duan
- Anterio Consult & Research GmbH, Augustaanlage 23, 68165 Mannheim, Germany
| | - Winfried Meining
- Lehrstuhl für Biologische Chemie, Technische Universität München, 85350 Freising-Weihenstephan, Germany
| | - Nicolas Foloppe
- Karolinska Institute, Department of Bioscience, Hälsovägen 7-9, S-14157 Huddinge, Sweden
| | - Lennart Nilsson
- Karolinska Institute, Department of Bioscience, Hälsovägen 7-9, S-14157 Huddinge, Sweden
| | - Adelbert Bacher
- Institute of Biochemistry and Food Chemistry, Food Chemistry Division, University of Hamburg, Grindelallee 117, D-20146 Hamburg, Germany
| | - Boris Illarionov
- Institute of Biochemistry and Food Chemistry, Food Chemistry Division, University of Hamburg, Grindelallee 117, D-20146 Hamburg, Germany
| | - Markus Fischer
- Institute of Biochemistry and Food Chemistry, Food Chemistry Division, University of Hamburg, Grindelallee 117, D-20146 Hamburg, Germany
| | - Rudolf Ladenstein
- Karolinska Institute, Department of Bioscience, Hälsovägen 7-9, S-14157 Huddinge, Sweden
| | - Mark Cushman
- Department of Medicinal Chemistry and Molecular Pharmacology, School of Pharmacy and Pharmaceutical Sciences, and The Purdue Center for Cancer Research, Purdue University, West Lafayette, Indiana, 47907, USA
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7
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Lairson LL, Henrissat B, Davies GJ, Withers SG. Glycosyltransferases: structures, functions, and mechanisms. Annu Rev Biochem 2008; 77:521-55. [PMID: 18518825 DOI: 10.1146/annurev.biochem.76.061005.092322] [Citation(s) in RCA: 1370] [Impact Index Per Article: 85.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023]
Abstract
Glycosyltransferases catalyze glycosidic bond formation using sugar donors containing a nucleoside phosphate or a lipid phosphate leaving group. Only two structural folds, GT-A and GT-B, have been identified for the nucleotide sugar-dependent enzymes, but other folds are now appearing for the soluble domains of lipid phosphosugar-dependent glycosyl transferases. Structural and kinetic studies have provided new insights. Inverting glycosyltransferases utilize a direct displacement S(N)2-like mechanism involving an enzymatic base catalyst. Leaving group departure in GT-A fold enzymes is typically facilitated via a coordinated divalent cation, whereas GT-B fold enzymes instead use positively charged side chains and/or hydroxyls and helix dipoles. The mechanism of retaining glycosyltransferases is less clear. The expected two-step double-displacement mechanism is rendered less likely by the lack of conserved architecture in the region where a catalytic nucleophile would be expected. A mechanism involving a short-lived oxocarbenium ion intermediate now seems the most likely, with the leaving phosphate serving as the base.
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Affiliation(s)
- L L Lairson
- Department of Chemistry, University of British Columbia, Vancouver, BC, Canada.
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8
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Selvam C, Goudet C, Oueslati N, Pin JP, Acher FC. l-(+)-2-Amino-4-thiophosphonobutyric Acid (l-thioAP4), a New Potent Agonist of Group III Metabotropic Glutamate Receptors: Increased Distal Acidity Affords Enhanced Potency. J Med Chem 2007; 50:4656-64. [PMID: 17722902 DOI: 10.1021/jm070400y] [Citation(s) in RCA: 52] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022]
Abstract
L-2-Amino-4-phosphonobutyric acid (l-AP4), l-2-amino-4-thiophosphonobutyric acid (l-thioAP4), and l-2-amino-4-(hydroxy)phosphinylbutyric acid (desmethylphosphinothricin, DMPT) were synthesized from protected vinylglycine. They were tested as agonists at group III metabotropic glutamate receptors (mGluR) along with phosphinothricin (PT). DMPT and PT display a much lower potency at mGlu4 receptor (EC50 = 4.0 and 1100 microM, respectively) in comparison to l-AP4 (EC50 = 0.08 microM), whereas l-thioAP4 has a 2-fold higher potency (EC50 = 0.039 microM). Similar rank orders of potency were observed at mGlu6,7 and mGlu8 receptors. The higher potency of l-thioAP4 is due to its stronger second acidity compared to l-AP4. These pKa values of 5.56 and 6.88, respectively, were determined using 31P NMR chemical shift variations. The second distal negative charge of l-AP4/l-thioAP4 probably provides stronger binding to specific basic residues of the binding sites of group III mGluRs, which stabilizes the active conformation of the receptor.
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Affiliation(s)
- Chelliah Selvam
- Laboratoire de Chimie et Biochimie Pharmacologiques et Toxicologiques, Université Paris Descartes, CNRS UMR-8601, 45 Rue des Saints-Pères, 75270 Paris Cedex 06, France
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9
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Pham V, Zhang W, Chen V, Whitney T, Yao J, Froese D, Friesen AD, Diakur JM, Haque W. Design and synthesis of novel pyridoxine 5'-phosphonates as potential antiischemic agents. J Med Chem 2003; 46:3680-7. [PMID: 12904072 DOI: 10.1021/jm0300678] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
On the basis of previous reports that the natural cofactor pyridoxal 5'-phosphate 1 appears to display cardioprotective properties, a series of novel mimetics of this cofactor were envisioned. As pyridoxal 5'-phosphate is a natural compound and is subject to biological degradation and elimination pathways, the objective was to generate active phosphonates that are potentially less light sensitive and more stable in vivo than the parent vitamer. Several phosphonates were designed and synthesized, and in particular, compounds 10 and 14 displayed similar biological traits to natural phosphate 1 in the rat model of regional myocardial ischemia and reperfusion. A reduction in infarct size was observed in animals treated with these compounds. In an effort to identify other relevant cardioprotective models in order to potentially define structure-activity relationships, these three compounds were tested in the rat working heart model. Compounds 1, 10, and 14 were compared to dichloroacetic acid (DCA) as positive control in this model. As with DCA, compounds 1, 10, and 14 were found to induce a shift from fatty acid oxidation toward glucose oxidation.
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Affiliation(s)
- Vinh Pham
- Medicure Inc. and CanamBioresearch Inc., 6-1200 Waverley Street, Winnipeg, Manitoba, Canada, R3T 0P4
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10
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Berkowitz DB, Bose M, Asher NG. A convergent triflate displacement approach to (alpha-monofluoroalkyl)phosphonates. Org Lett 2001; 3:2009-12. [PMID: 11418036 DOI: 10.1021/ol015983z] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
[reaction: see text] Treatment of primary alkyl triflates or iodides with the potassium salt of diethyl (alpha-fluoro-alpha-phenylsulfonylmethyl)phosphonate yields (alpha-fluoro-alpha-phenylsulfonylalkyl)phosphonates. These can be cleanly desulfonated, in a matter of minutes, with Na(Hg) in MeOH/THF/NaH(2)PO(4). This two-step procedure complements previously reported triflate displacement approaches to alpha-nonfluorinated and alpha,alpha-difluorinated phosphonates.
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Affiliation(s)
- D B Berkowitz
- Department of Chemistry, University of Nebraska, Lincoln, Nebraska 68588-0304, USA.
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11
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Toney MD. Computational studies on nonenzymatic and enzymatic pyridoxal phosphate catalyzed decarboxylations of 2-aminoisobutyrate. Biochemistry 2001; 40:1378-84. [PMID: 11170465 DOI: 10.1021/bi0012383] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
A computational study of nonenzymatic and enzymatic pyridoxal phosphate-catalyzed decarboxylation of 2-aminoisobutyrate (AIB) is presented. Four prototropic isomers of a model aldimine between AIB and 5'-deoxypyridoxal, with acetate interacting with the pyridine nitrogen, were employed in calculations of both gas phase and water model (PM3 and PM3-SM3) decarboxylation reaction paths. Calculations employing the transition state structures obtained for the four isomers allow the demonstration of stereoelectronic effects in transition state stabilization as well as a separation of the contributions of the Schiff base and pyridine ring moieties to this stabilization. The unprotonated Schiff base contribution (approximately 16 kcal/mol) is larger than that of the pyridine ring even when it is protonated (approximately 10 kcal/mol), providing an explanation of the catalytic power of pyruvoyl-dependent amino acid decarboxylases. An active site model of dialkylglycine decarboxylase was constructed and validated, and enzymatic decarboxylation reaction paths were calculated. The reaction coordinate is shown to be complex, with proton transfer from Lys272 to the coenzyme C4' likely simultaneous with C alpha--CO(2)(-) bond cleavage. The proposed concerted decarboxylation/proton-transfer mechanism provides a simple explanation for the observed specificity of this enzyme toward oxidative decarboxylation.
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Affiliation(s)
- M D Toney
- Department of Chemistry, University of California, One Shields Avenue, Davis, California 95616, USA.
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12
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Lequeux T, Lebouc F, Lopin C, Yang H, Gouhier G, Piettre SR. Sulfanyl- and selanyldifluoromethylphosphonates as a source of phosphonodifluoromethyl radicals and their addition onto alkenes. Org Lett 2001; 3:185-8. [PMID: 11430030 DOI: 10.1021/ol006746j] [Citation(s) in RCA: 46] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
[figure: see text] Two different strategies are shown to produce sulfanyl and selanyldifluoromethylphosphonates. Thus, treatment of sulfanyldichloromethylphosphonates by 3HF.NEt3 in the presence of zinc bromide produces the corresponding sulfanyldifluoromethylphosphonates. In addition, lithiation of difluoromethylphosphonates followed by quenching with phenylsulfanyl chloride, phenylselanyl chloride, or diphenyl diselenide yields the corresponding sulfanyl- and selanyldifluorophosphonates. Generation of phosphonodifluoromethyl radicals from such precursors in the presence of alkenes produces the expected adducts.
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Affiliation(s)
- T Lequeux
- Laboratoire de Chimie Moléculaire et Thioorganique, UMR-CNRS 6507, Université de Caen-ISMRA, 6 Bd du Maréchal Juin-F 14050 Caen, France.
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13
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Griessler R, D'Auria S, Tanfani F, Nidetzky B. Thermal denaturation pathway of starch phosphorylase from Corynebacterium callunae: oxyanion binding provides the glue that efficiently stabilizes the dimer structure of the protein. Protein Sci 2000; 9:1149-61. [PMID: 10892808 PMCID: PMC2144666 DOI: 10.1110/ps.9.6.1149] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/21/2022]
Abstract
Starch phosphorylase from Corynebacterium callunae is a dimeric protein in which each mol of 90 kDa subunit contains 1 mol pyridoxal 5'-phosphate as an active-site cofactor. To determine the mechanism by which phosphate or sulfate ions bring about a greater than 500-fold stabilization against irreversible inactivation at elevated temperatures (> or = 50 degrees C), enzyme/oxyanion interactions and their role during thermal denaturation of phosphorylase have been studied. By binding to a protein site distinguishable from the catalytic site with dissociation constants of Ksulfate = 4.5 mM and Kphosphate approximately 16 mM, dianionic oxyanions induce formation of a more compact structure of phosphorylase, manifested by (a) an increase by about 5% in the relative composition of the alpha-helical secondary structure, (b) reduced 1H/2H exchange, and (c) protection of a cofactor fluorescence against quenching by iodide. Irreversible loss of enzyme activity is triggered by the release into solution of pyridoxal 5'-phosphate, and results from subsequent intermolecular aggregation driven by hydrophobic interactions between phosphorylase subunits that display a temperature-dependent degree of melting of secondary structure. By specifically increasing the stability of the dimer structure of phosphorylase (probably due to tightened intersubunit contacts), phosphate, and sulfate, this indirectly (1) preserves a functional active site up to approximately 50 degrees C, and (2) stabilizes the covalent protein cofactor linkage up to approximately 70 degrees C. The effect on thermostability shows a sigmoidal and saturatable dependence on the concentration of phosphate, with an apparent binding constant at 50 degrees C of approximately 25 mM. The extra stability conferred by oxyanion-ligand binding to starch phosphorylase is expressed as a dramatic shift of the entire denaturation pathway to a approximately 20 degrees C higher value on the temperature scale.
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Affiliation(s)
- R Griessler
- Division of Biochemical Engineering, Institute of Food Technology, Universität für Bodenkultur Wien (BOKU), Austria
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