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Hill RA, Kouremenos K, Tull D, Maggi A, Schroeder A, Gibbons A, Kulkarni J, Sundram S, Du X. Bazedoxifene - a promising brain active SERM that crosses the blood brain barrier and enhances spatial memory. Psychoneuroendocrinology 2020; 121:104830. [PMID: 32858306 DOI: 10.1016/j.psyneuen.2020.104830] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/01/2020] [Accepted: 08/11/2020] [Indexed: 12/21/2022]
Abstract
Over 20 years of accumulated evidence has shown that the major female sex hormone 17β-estradiol can enhance cognitive functioning. However, the utility of estradiol as a therapeutic cognitive enhancer is hindered by its unwanted peripheral effects (carcinogenic). Selective estrogen receptor modulators (SERMs) avoid the unwanted effects of estradiol by acting as estrogen receptor antagonists in some tissues such as breast and uterus, but as agonists in others such as bone, and are currently used for the treatment of osteoporosis. However, understanding of their actions in the brain are limited. The third generation SERM bazedoxifene has recently been FDA approved for clinical use with an improved biosafety profile. However, whether bazedoxifene can enter the brain and enhance cognition is unknown. Using mice, the current study aimed to explore if bazedoxifene can 1) cross the blood-brain barrier, 2) rescue ovariectomy-induced hippocampal-dependent spatial memory deficit, and 3) activate neural estrogen response element (ERE)-dependent gene transcription. Using liquid chromatography-mass spectrometry (LC-MS), we firstly demonstrate that a peripheral injection of bazedoxifene can enter the brain. Secondly, we show that an acute intraperitoneal injection of bazedoxifene can rescue ovariectomy-induced spatial memory deficits. And finally, using the ERE-luciferase reporter mouse, we show in vivo that bazedoxifene can activate the ERE in the brain. The evidence shown here suggest bazedoxifene could be a viable cognitive enhancer with promising clinical applicability.
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Affiliation(s)
- R A Hill
- Department of Psychiatry, Monash University, Clayton, VIC, 3168, Australia; Florey Institute for Neuroscience and Mental Health, Parkville, VIC, 3052, Australia.
| | - K Kouremenos
- Metabolomics Australia, Bio21 Molecular Science & Biotechnology Institute, Parkville, VIC, 3052, Australia
| | - D Tull
- Metabolomics Australia, Bio21 Molecular Science & Biotechnology Institute, Parkville, VIC, 3052, Australia
| | - A Maggi
- Department of Pharmacological and Biomolecular Sciences, University of Milan, Milan, 20133, Italy
| | - A Schroeder
- Department of Psychiatry, Monash University, Clayton, VIC, 3168, Australia
| | - A Gibbons
- Department of Psychiatry, Monash University, Clayton, VIC, 3168, Australia
| | - J Kulkarni
- Monash Alfred Psychiatry Research Centre, Monash University, St Kilda, VIC, 3004, Australia
| | - S Sundram
- Department of Psychiatry, Monash University, Clayton, VIC, 3168, Australia
| | - X Du
- Department of Psychiatry, Monash University, Clayton, VIC, 3168, Australia; Florey Institute for Neuroscience and Mental Health, Parkville, VIC, 3052, Australia
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2
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Best S, DeSouza D, Kersbergen A, Dayalan S, Tull D, Policheni A, Gray D, Ritchie M, McConville M, Sutherland K. PO-210 Synergy between the KEAP1/NRF2 and PI3K pathways drives non-small cell lung cancer with an altered metabolism. ESMO Open 2018. [DOI: 10.1136/esmoopen-2018-eacr25.728] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/03/2022] Open
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3
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Rasmiena A, Stefanovic N, Huynh K, Tan R, Barlow C, Tull D, deHaan J, Meikle P. Attenuation of atherosclerosis in ApoE- and ApoE/GPX1-deficient mice by plasmalogen enrichment. Atherosclerosis 2015. [DOI: 10.1016/j.atherosclerosis.2015.04.051] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 10/23/2022]
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4
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Vodstrcil LA, Rupasinghe T, Tull D, Worthington K, Chen MY, Huston WM, Fairley CK, McConville M, Tabrizi SN, Hocking JS. P2.082 Post-Treatment Detection of Azithromycin in High-Vaginal Swabs Using Liquid Chromatography and Tandem Mass Spectrometry (LC-MS/MS). Br J Vener Dis 2013. [DOI: 10.1136/sextrans-2013-051184.0346] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/03/2022]
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5
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Decuypere S, Pyke J, Tull D, Buddhisa S, McConville M, Blackwell J, Lertmemongkolchai G. Metabolomics based biomarker discovery for infectious diseases, the case of melioidosis. Int J Infect Dis 2012. [DOI: 10.1016/j.ijid.2012.05.810] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/01/2022] Open
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6
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Gottschalk TE, Tull D, Aghajari N, Haser R, Svensson B. Specificity modulation of barley alpha-amylase through biased random mutagenesis involving a conserved tripeptide in beta --> alpha loop 7 of the catalytic (beta/alpha)(8)-barrel domain. Biochemistry 2001; 40:12844-54. [PMID: 11669621 DOI: 10.1021/bi0108608] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
The relative specificity and bond cleavage pattern of barley alpha-amylase 1 (AMY1) were dramatically changed by mutation in F(286)VD that connected beta-strand 7 of the catalytic (beta/alpha)(8)-barrel to a succeeding 3(10)-helix. This conserved tripeptide of the otherwise variable beta --> alpha segment 7 lacked direct ligand contact, but the nearby residues His290 and Asp291 participated in transition-state stabilization and catalysis. On the basis of sequences of glycoside hydrolase family 13, a biased random mutagenesis protocol was designed which encoded 174 putative F(286)VD variants of C95A-AMY1, chosen as the parent enzyme to avoid inactivating glutathionylation by the yeast host. The FVG, FGG, YVD, LLD, and FLE mutants showed 12-380 and 1.8-33% catalytic efficiency (k(cat)/K(m)) toward 2-chloro-4-nitrophenyl beta-D-maltoheptaoside and amylose DP17, respectively, and 0.5-50% activity for insoluble starch compared to that of C95A-AMY1. K(m) and k(cat) were decreased 2-9- and 1.3-83-fold, respectively, for the soluble substrates. The starch:oligosaccharide and amylose:oligosaccharide specificity ratios were 13-172 and 2.4-14 for mutants and 520 and 27 for C95A-AMY1, respectively. The FVG mutant released 4-nitrophenyl alpha-D-maltotrioside (PNPG(3)) from PNPG(5), whereas C95A-AMY1 produced PNPG and PNPG(2). The mutation thus favored interaction with the substrate aglycon part, while products from PNPG(6) reflected the fact that the mutation restored binding at subsite -6 which was lost in C95A-AMY1. The outcome of this combined irrational and rational protein engineering approach was evaluated considering structural accommodation of mutant side chains. FVG and FGG, present in the most active variants, represented novel sequences. This emphasized the worth of random mutagenesis and launched flexibility as a goal for beta --> alpha loop 7 engineering in family 13.
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Affiliation(s)
- T E Gottschalk
- Department of Chemistry, Carlsberg Laboratory, Gamle Carlsberg Vej 10, DK-2500 Copenhagen Valby, Denmark
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7
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Tull D, Gottschalk TE, Svendsen I, Kramhøft B, Phillipson BA, Bisgård-Frantzen H, Olsen O, Svensson B. Extensive N-glycosylation reduces the thermal stability of a recombinant alkalophilic bacillus alpha-amylase produced in Pichia pastoris. Protein Expr Purif 2001; 21:13-23. [PMID: 11162382 DOI: 10.1006/prep.2000.1348] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
Abstract
Alkalophilic Bacillus alpha-amylase (ABA) was produced in the yeast Pichia pastoris with a yield of 50 mg L(-1) of culture supernatant. The recombinant protein, rABA, was glycosylated at seven of the nine sites for potential N-glycosylation as identified by automated peptide sequencing and MALDI-TOF MS of tryptic fragments. The number of hexose units within each glycan chain was found to vary from 8 to 18 as calculated from the masses of glycosylated peptide fragments. Temperature stability measurements in the absence of substrate showed that the T(50) of glycosylated rABA and its endoglycosidase H-deglycosylated form was 76 degrees C while that of ABA purified from Bacillus was 89 degrees C thus demonstrating that the original temperature stability of ABA was not retained by rABA. The relative thermoperformance, i.e., the activity at 80 degrees C relative to that at 37 degrees C was 0.9 +/- 0.3 for rABA. Removal of all seven N-linked glycans by endoglycosidase H increased the relative thermoperformance to 2.4 +/- 0.6, compared to the value of 3.5 +/- 1.1 for ABA. Thus, removal of the N-linked glycans did not improve the thermostability of rABA but modified its thermoperformance to approach that of the original Bacillus enzyme. rABA had the highest activity around pH 6. Treatment of rABA with endoglycosidase H shifted the pH activity profile in a more alkaline direction approaching the pH activity profile of ABA.
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Affiliation(s)
- D Tull
- Department of Chemistry, Carlsberg Laboratory, Gamle Carlsberg Vej 10, DK-2500 Copenhagen Valby, Denmark
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8
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Gottschalk TE, Fierobe HP, Mirgorodskaya E, Clarke AJ, Tull D, Sigurskjold BW, Christensen T, Payre N, Frandsen TP, Juge N, McGuire KA, Cottaz S, Roepstorff P, Driguez H, Williamson G, Svensson B. Structure, function and protein engineering of starch-degrading enzymes. Biochem Soc Trans 1998; 26:198-204. [PMID: 9649747 DOI: 10.1042/bst0260198] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/08/2023]
Affiliation(s)
- T E Gottschalk
- Department of Chemistry, Carlsberg Laboratory, Copenhagen, Valby, Denmark
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9
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Birsan C, Johnson P, Joshi M, MacLeod A, McIntosh L, Monem V, Nitz M, Rose DR, Tull D, Wakarchuck WW, Wang Q, Warren RA, White A, Withers SG. Mechanisms of cellulases and xylanases. Biochem Soc Trans 1998; 26:156-60. [PMID: 9649739 DOI: 10.1042/bst0260156] [Citation(s) in RCA: 38] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/08/2023]
Affiliation(s)
- C Birsan
- Protein Engineering Network of Centres of Excellence of Canada, Vancouver, B.C., Canada
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10
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Fierobe HP, Clarke AJ, Tull D, Svensson B. Enzymatic properties of the cysteinesulfinic acid derivative of the catalytic-base mutant Glu400-->Cys of glucoamylase from Aspergillus awamori. Biochemistry 1998; 37:3753-9. [PMID: 9521694 DOI: 10.1021/bi972232p] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
The pKa of the catalytic base was lowered and its distance to the general acid catalyst, Glu179, was increased in the glucoamylase from Aspergillus awamori by replacing the catalytic base Glu400 with cysteine followed by oxidation to cysteinesulfinic acid [Fierobe, H.-P., Mirgorodskaya, E., McGuire, K. A., Roepstorff, P., Svensson, B. and Clarke, A. J. (1998) Biochemistry 37, 3743-3752. 1H NMR spectroscopy demonstrated that the oxidized mutant Glu400-->Cys-SO2H glucoamylase, like the wild-type, catalyzed hydrolysis with inversion of the anomeric configuration of the product. Relative to the catalytic base mutant Glu400-->Cys, the Cys400-SO2H glucoamylase had 700 times higher kcat toward maltose, while K(m) was unchanged. Compared to wild-type glucoamylase, the Cys400-SO2H derivative had kcat values of 150-190% and 85-320% on malto- and isomaltooligosaccharides, respectively, while K(m) values were similar to those of wild-type with the two disaccharides and 3.5-5.5- and 1.8-2.5-fold higher for the longer malto- and isomaltooligosaccharides substrates, respectively. The pH-activity dependence at saturating concentration of maltose indicated that the pKa of the catalytic base Cys400-SO2H was about 0.5 pH unit lower than that of wild-type Glu400. The Ki of Cys400-SO2H glucoamylase for the pseudotetrasaccharide and potent inhibitor acarbose increased more than 10(4)-fold, but Ki values of the mono- and disaccharide analogues 1-deoxynojirimycin and beta-O-methylacarviosinide were unchanged, suggesting perturbation at binding subsites beyond the catalytic center. A distinct property of Cys400-SO2H glucoamylase was the catalysis of the condensation of beta-D-glucopyranosyl fluoride and subsequent hydrolysis of the product to beta-glucose, under conditions where this was not detected for the wild-type enzyme.
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Affiliation(s)
- H P Fierobe
- Department of Chemistry, Carlsberg Laboratory, Copenhagen Valby, Denmark
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11
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MacLeod AM, Tull D, Rupitz K, Warren RA, Withers SG. Mechanistic consequences of mutation of active site carboxylates in a retaining beta-1,4-glycanase from Cellulomonas fimi. Biochemistry 1996; 35:13165-72. [PMID: 8855954 DOI: 10.1021/bi9610616] [Citation(s) in RCA: 59] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Abstract
The exoglucanase/xylanase Cex from Cellulomonas fimi is a retaining glycosidase which functions via a two-step mechanism involving the formation and hydrolysis of a covalent glycosyl-enzyme intermediate. The roles of three conserved active site carboxylic acids in this enzyme have been probed by detailed kinetic analysis of mutants modified at these three positions. Elimination of the catalytic nucleophile (E233A) results in an essentially inactive enzyme, consistent with the important role of this residue. However addition of small anions such as azide or formate restores activity, but as an inverting enzyme since the product formed under these conditions is the alpha-glycosyl azide. Shortening of the catalytic nucleophile (E233D) reduces the rates of both formation and hydrolysis of the glycosyl-enzyme intermediate some 3000-4000-fold. Elimination of the acid/base catalyst (E127A) yields a mutant for which the deglycosylation step is slowed some 200-300-fold as a consequence of removal of general base catalysis, but with little effect on the transition state structure at the anomeric center. Effects on the glycosylation step due to removal of the acid catalyst depend on the aglycon leaving group ability, with minimal effects on substrates requiring no general acid catalysis but large (> 10(5)-fold) effects on substrates with poor leaving groups. The Brønsted beta 1g value for hydrolysis of aryl cellobiosides was much larger (beta 1g approximately -1) for the mutant than for the wild-type enzyme (beta 1g = -0.3), consistent with removal of protonic assistance. The pH-dependence was also significantly perturbed. Mutation of a third conserved active site carboxylic acid (E123A) resulted in rate reductions of up to 1500-fold on poorer substrates, which could be largely restored by addition of azide, but without the formation of glycosyl azide products. These results suggest a simple strategy for the identification of the key active site nucleophile and acid/base catalyst residues in glycosidases without resort to active site labeling.
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Affiliation(s)
- A M MacLeod
- Department of Microbiology and Immunology, University of British Columbia, Vancouver, Canada
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12
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Juge N, Andersen JS, Tull D, Roepstorff P, Svensson B. Overexpression, purification, and characterization of recombinant barley alpha-amylases 1 and 2 secreted by the methylotrophic yeast Pichia pastoris. Protein Expr Purif 1996; 8:204-14. [PMID: 8812863 DOI: 10.1006/prep.1996.0093] [Citation(s) in RCA: 63] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Abstract
Recombinant barley alpha-amylase isozymes 1 and 2 were secreted by Pichia pastoris at up to 50 and 1 mg/liter, respectively, representing approximately a 50-fold increase compared to the levels of the heterologous expression by Saccharomyces cerevisiae. The cDNA clones E or pM/C encoding isozymes 1 and 2, respectively, were placed under the control of regulatory sequences from the Pichia AOX1 gene in the vector pHIL-D2. Both isozymes were effectively secreted to the medium as directed by their own signal sequences and easily purified to homogeneity in quantitative yield by affinity chromatography on beta-cyclodextrin-Sepharose. The N-terminal sequence, pI, and Mr indicated that native-like processing took place. Electrospray ionization mass spectrometry, however, revealed microheterogeneity for recombinant isozyme 1. While Mr of one recombinant isozyme 1 form of 45,452 was in excellent agreement with a value of 45,447 calculated from the sequence, liquid chromatography/mass spectrometry of endo Lys C-generated peptides followed by tandem mass spectrometry on a nanoelectrospray ionization/mass spectrometry/mass spectrometry system identified additional recombinant isozyme 1 forms to be glycosylated on Thr410, N-acetylated on His1, S-glutathionylated on Cys95, or C-terminally truncated of -412RS, -411QRS, and -410LQRS. The recombinant enzymes and the alpha-amylases from barley malt closely resembled each other in enzymatic activity on insoluble Blue Starch, amylose of degree of polymerization 17, and 2-chloro-4-nitrophenyl beta-D-maltoheptaoside as well as in Ca2+ dependency of activity. Pichia pastoris thus produced in high yields recombinant alpha-amylase that is similar with respect to structure and function to the enzyme purified from malt extracts. This greatly facilitates future mutational analysis of barley alpha-amylase in order to probe structure/function relationships.
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Affiliation(s)
- N Juge
- Department of Chemistry, Carlsberg Laboratory, Gamle Carlsberg Vej 10, Copenhagen Valby, DK-2500, Denmark
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13
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White A, Tull D, Johns KL, Withers SG, Rose DR. Structural implication of two saccharide conformations in the active site of a β-glycosidase. Acta Crystallogr A 1996. [DOI: 10.1107/s0108767396091489] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022] Open
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14
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Tull D, Burgoyne DL, Chow DT, Withers SG, Aebersold R. A mass spectrometry-based approach for probing enzyme active sites: identification of Glu 127 in Cellulomonas fimi exoglycanase as the residue modified by N-bromoacetyl cellobiosylamine. Anal Biochem 1996; 234:119-25. [PMID: 8714589 DOI: 10.1006/abio.1996.0063] [Citation(s) in RCA: 20] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023]
Abstract
We have identified the residue in Cellulomonas fimi exoglycanase modified by N-bromoacetyl cellobiosylamine as Glu 127 using a new combination of experimental approaches. The enzyme was quantitatively inhibited with the affinity label N-bromoacetyl cellobiosylamine and cleaved with pepsin. The N-acetyl cellobiosylamine-modified peptide was identified by comparative peptide mapping of the digests derived from labeled and unlabeled proteins by reverse-phase high-performance liquid chromatography connected online to an electrospray ionization mass spectrometer. The modified residue in the labeled peptide was determined by using a novel protein sequencing chemistry which is based on monitoring the amino acid derivatives released by stepwise peptide degradation using electrospray ionization mass spectrometry. Tandem mass spectrometry was used for further structural characterization of the cleaved residue. We show that the residue modified by N-bromoacetyl cellobiosylamine is Glu 127. This residue has been identified previously as the acid-base catalyst by using a combination of mutagenic and kinetic analyses. Our results therefore demonstrate the usefulness of this type of affinity label in identifying important catalytic residues in glycosidases and suggest that this new experimental approach can be applied generally to any labeled protein in which the mass of the label is known and thus represents an alternative approach to the current methods used to identify labeled residues within proteins.
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Affiliation(s)
- D Tull
- Department of Chemistry, University of British Columbia, Vancouver
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15
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White A, Tull D, Johns K, Withers SG, Rose DR. Crystallographic observation of a covalent catalytic intermediate in a beta-glycosidase. Nat Struct Biol 1996; 3:149-54. [PMID: 8564541 DOI: 10.1038/nsb0296-149] [Citation(s) in RCA: 141] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
The three-dimensional structure of a catalytically competent glycosyl-enzyme intermediate of a retaining beta-1,4-glycanase has been determined at a resolution of 1.8 A by X-ray diffraction. A fluorinated slow substrate forms an alpha-D-glycopyranosyl linkage to one of the two invariant carboxylates, Glu 233, as supported in solution by 19F-NMR studies. The resulting ester linkage is coplanar with the cyclic oxygen of the proximal saccharide and is inferred to form a strong hydrogen bond with the 2-hydroxyl of that saccharide unit in natural substrates. The active-site architecture of this covalent intermediate gives insights into both the classical double-displacement catalytic mechanism and the basis for the enzyme's specificity.
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Affiliation(s)
- A White
- Protein Engineering Network of Centres of Excellence, Ontario Cancer Institute, Toronto, Canada
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16
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Tull D, Miao S, Withers SG, Aebersold R. Identification of derivatized peptides without radiolabels: tandem mass spectrometric localization of the tagged active-site nucleophiles of two cellulases and a beta-glucosidase. Anal Biochem 1995; 224:509-14. [PMID: 7733452 DOI: 10.1006/abio.1995.1080] [Citation(s) in RCA: 24] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Abstract
A new method that uses nonradioactive active site-directed enzyme inactivators and high-performance liquid chromatography-electrospray ionization tandem mass spectrometry (HPLC-ESIMS/MS) to identify labeled peptides in a proteolytic digest is described. This method relies upon the fragmentation of labeled peptides in a predictable and reproducible manner in the collision cell of a tandem mass spectrometer. The exoglycanase from Cellulomonas fimi, endoglucanase C from Clostridium thermocellum, and the beta-glucosidase from Agrobacterium faecalis were labeled using 2-deoxy-2-halo-beta-glycosides, digested with pepsin, and subjected to HPLC-ESIMS/MS analysis, scanning in the neutral loss mode. Under these conditions only peptides that lose the (known) mass of the label are detected. Preliminary identification of candidate peptides can be achieved from the mass measured, in combination with the known sequence of the protein. Peptide identity can be confirmed through subsequent sequencing, either via further tandem MS experiments or via the Edman degradation. In all cases the peptides identified in this manner were consistent with those identified by the standard radioactive method. This mass spectrometric method represents a rapid, nonradioisotopic solution to the problem of identifying a modified peptide in a complex mixture. The technique is also sensitive, requiring only picomole amounts of protein.
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Affiliation(s)
- D Tull
- Department of Chemistry, University of British Columbia, Vancouver, Canada
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17
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Abstract
The exoglucanase/xylanase from Cellulomonas fimi (Cex) has been subjected to a detailed kinetic investigation with a range of aryl beta-D-glycoside substrates. This enzyme hydrolyzes its substrates with net retention of anomeric configuration, and thus it presumably follows a double-displacement mechanism. Values of kcat are found to be invariant with pH whereas kcat/Km is dependent upon two ionizations of pKa = 4.1 and 7.7. The substrate preference of the enzyme increases in the order glucosides < cellobiosides < xylobiosides, and kinetic studies with a range of aryl glucosides and cellobiosides have allowed construction of Broensted relationships for these substrate types. A strong dependence of both kcat (beta 1g = -1) and kcat/Km (beta 1g = -1) upon leaving group ability is observed for the glucosides, indicating that formation of the intermediate is rate-limiting. For the cellobiosides a biphasic, concave downward plot is seenj for kcat, indicating a change in rate-determining step across the series. Pre-steady-state kinetic experiments allowed construction of linear Broensted plots of log k2 and log (k2/Kd) for the cellobiosides of modest (beta 1g = -0.3) slope. These results are consistent with a double-displacement mechanism in which a glycosyl-enzyme intermediate is formed and hydrolyzed via oxocarbonium ion-like transition states. Secondary deuterium kinetic isotope effects and inactivation experiments provide further insight into transition-state structures and, in concert with beta 1g values, reveal that the presence of the distal sugar moiety in cellobiosides results in a less highly charged transition state.(ABSTRACT TRUNCATED AT 250 WORDS)
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Affiliation(s)
- D Tull
- Department of Chemistry, University of British Columbia, Vancouver, Canada
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18
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Affiliation(s)
- T S Black
- Department of Chemistry, University of British Columbia, Vancouver, Canada
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19
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McCarter JD, Adam MJ, Braun C, Namchuk M, Tull D, Withers SG. Syntheses of 2-deoxy-2-fluoro mono- and oligo-saccharide glycosides from glycals and evaluation as glycosidase inhibitors. Carbohydr Res 1993; 249:77-90. [PMID: 8252556 DOI: 10.1016/0008-6215(93)84061-a] [Citation(s) in RCA: 46] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023]
Abstract
Several fluorinated oligosaccharides, including 2-deoxy-2-fluoro derivatives of cellobiose, maltose, and maltotriose were synthesized by the action of fluorine or acetyl hypofluorite on the corresponding glycal peracetates. Temperature effects on the stereoselectivities of these reactions were examined. Addition of acetyl hypofluorite to several 2-substituted glycals in the gluco or galacto series gave 2,2-disubstituted arabino- or lyxo-hexose derivatives; 3,4,6-tri-O-acetyl-2-fluoro-D-glucal or the analogous galactal yielded 2-deoxy-2,2-difluoro arabino- or lyxo-hexose peracetates, whereas 2-acetoxy-3,4,6-tri-O-acetyl-D-glucal or the analogous galactal gave 2(R)-2-acetoxy-2-fluoro-arabino- or lyxo-hexose peracetates, respectively. 2-Acetamido-3,4,6-tri-O-acetyl-D-glucal gave 2(R)-2-acetamido-2-acetoxy-3,4,6-tri-O-acetyl-alpha-D-arabino-hexopyrano syl fluoride. 2,4-Dinitrophenyl 2-deoxy-2-fluoro-beta-cellobioside was an inactivator of the exoglucanase from Cellulomonas fimi while 2-deoxy-2-fluoro-alpha-maltosyl and alpha-maltotriosyl fluorides were slow substrates of human pancreatic alpha-amylase and rabbit muscle glycogen debranching enzyme, respectively.
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Affiliation(s)
- J D McCarter
- Department of Chemistry, University of British Columbia, Vancouver, Canada
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Wang Q, Tull D, Meinke A, Gilkes NR, Warren RA, Aebersold R, Withers SG. Glu280 is the nucleophile in the active site of Clostridium thermocellum CelC, a family A endo-beta-1,4-glucanase. J Biol Chem 1993; 268:14096-102. [PMID: 8100226] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023] Open
Abstract
A new mechanism-based inactivator of beta-1,4-glucanases, 2',4'-dinitrophenyl-2-deoxy-2-fluoro-beta-D-cellobioside, was synthesized and used to trap the intermediate formed during catalysis by endoglucanase C (CelC) from Clostridium thermocellum. Ion spray mass spectrometry confirmed the 1:1 stoichiometry of the incorporation of the inactivator into the enzyme. Inactivation followed the required pseudo first-order kinetic behavior and kinetic parameters for the process were determined. Although the intermediate trapped was relatively stable (t1/2 = 25 h), turnover was facilitated by transglycosylation following the addition of phenyl-beta-D-thiocellobioside and cellobiose, thus demonstrating the catalytic competence of the trapped intermediate. The nucleophilic amino acid residue involved was identified as Glu280 by labeling the enzyme with tritiated inactivator, cleaving it into peptides and sequencing the radiolabeled peptide. Ion spray mass spectrometric analysis of the peptide confirmed the sequence and the mode of attachment of the sugar to the peptide. Alignment of all known related beta-1,4-glucanases showed that Glu280 is strictly conserved in family A enzymes, consistent with its key role in catalysis.
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Affiliation(s)
- Q Wang
- Department of Chemistry, University of British Columbia, Vancouver, Canada
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Wang Q, Tull D, Meinke A, Gilkes N, Warren R, Aebersold R, Withers S. Glu280 is the nucleophile in the active site of Clostridium thermocellum CelC, a family A endo-beta-1,4-glucanase. J Biol Chem 1993. [DOI: 10.1016/s0021-9258(19)85213-4] [Citation(s) in RCA: 90] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022] Open
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Tull D, Withers SG, Gilkes NR, Kilburn DG, Warren RA, Aebersold R. Glutamic acid 274 is the nucleophile in the active site of a "retaining" exoglucanase from Cellulomonas fimi. J Biol Chem 1991; 266:15621-5. [PMID: 1678739] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022] Open
Abstract
In addition to its known substrate activity with p-nitrophenyl beta-cellobioside, the exoglucanase from Cellulomonas fimi has been shown to utilize substituted phenyl beta-glucosides as substrates, of which the best is 2',4'-dinitrophenyl beta-D-glucopyranoside. The enzyme can be inactivated by treatment with 2',4'-dinitrophenyl 2-deoxy-2-fluoro-beta-D-glucopyranoside, by trapping of the covalent intermediate in catalysis, as has been shown for a beta-glucosidase (Withers, S.G., and Street, I.P. (1988) J. Am. Chem. Soc. 110, 8551-8553). The intermediate formed is stable but can undergo turnover in the presence of cellobiose, reactivating the enzyme by transglycosylation. Using a tritium-labeled inactivator it has been possible to isolate and sequence a radiolabeled peptide from this enzyme, and the active site nucleophile has been identified as glutamic acid residue 274. This glutamic acid residue and its sequentially proximal amino acids are absolutely conserved in the homologous family F of cellulases.
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Affiliation(s)
- D Tull
- Department of Chemistry, University of British Columbia, Vancouver, Canada
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Tull D, Withers S, Gilkes N, Kilburn D, Warren R, Aebersold R. Glutamic acid 274 is the nucleophile in the active site of a “retaining” exoglucanase from Cellulomonas fimi. J Biol Chem 1991. [DOI: 10.1016/s0021-9258(18)98451-6] [Citation(s) in RCA: 102] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022] Open
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