Carica papaya Glutamine Cyclotransferase Belongs to a Novel Plant Enzyme Subfamily: Cloning and Characterization of the Recombinant Enzyme

Dahl, Søren; Slaughter, Clive A.; Lauritzen, Conni; Bateman, Robert C.; Connerton, Ian F.; Pedersen, John

doi:10.1006/prep.2000.1273

Cited by 38 publications

(43 citation statements)

References 30 publications

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“…5) The gene corresponding to GGC has never been identified from plants. Genes encoding glutaminyl cyclotransferase (QCT), which converts Gln and N-terminal glutaminyl residues in peptides to 5OP and 5OP residues, were identified from papaya (Carica papaya; Dahl et al, 2000) and Arabidopsis (Schilling et al, 2007). The papaya and Arabidopsis QCT were much more active in converting N-terminal Gln than Glu to 5OP (Schilling et al, 2004(Schilling et al, , 2007.…”

Section: Ggc Enzyme Kinetics With Gsh and G-ecmentioning

confidence: 99%

Aγ-Glutamyl Transpeptidase-Independent Pathway of Glutathione Catabolism to Glutamate via 5-Oxoproline in Arabidopsis

et al. 2008

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The degradation pathway of glutathione (GSH) in plants is not well understood. In mammals, GSH is predominantly metabolized through the g-glutamyl cycle, where GSH is degraded by the sequential reaction of g-glutamyl transpeptidase (GGT), g-glutamyl cyclotransferase, and 5-oxoprolinase to yield glutamate (Glu) and dipeptides that are subject to peptidase action. In this study, we examined if GSH is degraded through the same pathway in Arabidopsis (Arabidopsis thaliana) as occurs in mammals. In Arabidopsis, the oxoprolinase knockout mutants (oxp1-1 and oxp1-2) accumulate more 5-oxoproline (5OP) and less Glu than wild-type plants, suggesting substantial metabolite flux though 5OP and that 5OP is a major contributor to Glu steady-state levels. In the ggt1-1/ggt4-1/oxp1-1 triple mutant with no GGT activity in any organs except young siliques, the 5OP concentration in leaves was not different from that in oxp1-1, suggesting that GGTs are not major contributors to 5OP production in Arabidopsis. 5OP formation strongly tracked the level of GSH in Arabidopsis plants, suggesting that GSH is the precursor of 5OP in a GGT-independent reaction. Kinetics analysis suggests that g-glutamyl cyclotransferase is the major source of GSH degradation and 5OP formation in Arabidopsis. This discovery led us to propose a new pathway for GSH turnover in plants where GSH is converted to 5OP and then to Glu by the combined action of g-glutamyl cyclotransferase and 5-oxoprolinase in the cytoplasm.

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Section: Ggc Enzyme Kinetics With Gsh and G-ecmentioning

confidence: 99%

Aγ-Glutamyl Transpeptidase-Independent Pathway of Glutathione Catabolism to Glutamate via 5-Oxoproline in Arabidopsis

et al. 2008

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“…Whereas plant QC consists almost solely of ␤-sheet structure, mammalian QCs are predicted to possess an ␣/␤-fold (8 -10). Furthermore, plant QC does not share sequence or structural homology to other plant enzymes, belonging, apparently, to a separate enzyme subfamily (4). Mammalian QCs, however, exhibit remarkable homology toward bacterial aminopeptidases, suggesting their evolutionary origin in this protein family (9).…”

mentioning

confidence: 95%

“…Previously, the formation of N-terminal pyroglutamate from glutamine was assumed to proceed spontaneously (1). However, the QCs were identified more recently as catalysts of the reaction in both mammals and plants (2)(3)(4)(5). Generally, QCs from both mammalian and plant sources appear to be very similar monomeric proteins that are expressed in the secretory pathways and have similar molecular masses, ϳ33 and ϳ40 kDa, respectively (6,7).…”

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confidence: 99%

Identification of Human Glutaminyl Cyclase as a Metalloenzyme

Schilling

Niestroj

Rahfeld

et al. 2003

Journal of Biological Chemistry

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Glutaminyl cyclases (QC) 1 (EC 2.3.2.5) are acyltransferases present in animals and plants that catalyze the conversion of N-terminal glutaminyl residues into pyroglutamic acid with the concomitant liberation of ammonia (Scheme 1). Several peptide hormones and proteins carry N-terminal pyroglutamyl residues. Previously, the formation of N-terminal pyroglutamate from glutamine was assumed to proceed spontaneously (1). However, the QCs were identified more recently as catalysts of the reaction in both mammals and plants (2-5). Generally, QCs from both mammalian and plant sources appear to be very similar monomeric proteins that are expressed in the secretory pathways and have similar molecular masses, ϳ33 and ϳ40 kDa, respectively (6, 7). Their primary structures, however, reveal no sequence homology, and the enzymes feature completely different folding patterns. Whereas plant QC consists almost solely of ␤-sheet structure, mammalian QCs are predicted to possess an ␣/␤-fold (8 -10). Furthermore, plant QC does not share sequence or structural homology to other plant enzymes, belonging, apparently, to a separate enzyme subfamily (4). Mammalian QCs, however, exhibit remarkable homology toward bacterial aminopeptidases, suggesting their evolutionary origin in this protein family (9).Investigating the substrate specificity of both enzymes, we recently found differences between papaya and human QC (24). Although the catalysis of cyclization of and the inhibition by modified N-terminal residues were quite different, both enzymes catalyzed the cyclization of oligopeptides with similar specificity rate constants. Moreover, they also catalyzed the formation of a five-membered lactam ring from L-␤-homoglutaminyl peptides. Based on the present state of knowledge, it is assumed that plant and animal QCs catalyze the formation of N-terminal pyroglutamic acid (pGlu) residues by enabling the intramolecular cyclization of the glutaminyl residue in a noncovalent manner (11,12). However, the results of the substrate specificity study revealed differences in substrate recognition by both enzymes.Thus, a more detailed analysis of the inhibition pattern of plant and human QCs should help to deepen our understanding of QC catalysis. To date, however, systematic inhibitor data exist only for plant QC, which is competitively inhibited by peptides containing an N-terminal proline residue (13), whereas human QC was shown to be inactivated by 1,10-phenanthroline and reduced 6-methylpterin (3). Thus, we investigated the inhibiting potency of heterocyclic compounds from different structural classes. Among them, imidazole and structurally related compounds were found to be the most efficient competitive inhibitors of human QC. The data provide the first insights into enzyme/inhibitor interactions, offer clues for further optimization of the inhibitory structure, and reveal novel aspects of human QC catalysis.

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“…Currently, pQC protein samples are obtained primarily by purification of the latex of C. papaya, 22 because it was reported that the expression of recombinant pQC in E. coli cells is very difficult, and the expression in insect cells gave very poor yields. 29 Here, we describe the efficient production in E. coli cells of a type I QC from the plant pathogenic bacterium Xanthomonas campestris. We also report the 1.44-Å-resolution crystal structure of this bacterial QC.…”

Section: Introductionmentioning

confidence: 99%

Crystal Structure and Functional Analysis of the Glutaminyl Cyclase from Xanthomonas campestris

Huang

Wang

et al. 2010

Journal of Molecular Biology

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Carica papaya Glutamine Cyclotransferase Belongs to a Novel Plant Enzyme Subfamily: Cloning and Characterization of the Recombinant Enzyme

Cited by 38 publications

References 30 publications

Aγ-Glutamyl Transpeptidase-Independent Pathway of Glutathione Catabolism to Glutamate via 5-Oxoproline in Arabidopsis

Aγ-Glutamyl Transpeptidase-Independent Pathway of Glutathione Catabolism to Glutamate via 5-Oxoproline in Arabidopsis

Identification of Human Glutaminyl Cyclase as a Metalloenzyme

Crystal Structure and Functional Analysis of the Glutaminyl Cyclase from Xanthomonas campestris

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