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- Cristea, Mirela, 1976-
(författare)
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Expression of Manganese Lipoxygenase and Site-Directed Mutagenesis of Catalytically Important Amino Acids : Studies on Fatty Acid Dioxygenases
- 2006
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Polyunsaturated fatty acids can be bioactivated by two families of dioxygenases, which either contain non-heme iron (lipoxygenases) or heme (cyclooxygenases, linoleate diol synthases and α-dioxygenases).Lipoxygenases and their products play important roles in the pathophysiology of plants and fungi. The only known lipoxygenase with catalytic manganese (Mn-lipoxygenase) is secreted by a devastating root pathogen of wheat, the Take-all fungus Gaeumannomyces graminis. Its mycelia also contains linoleate diol synthase (LDS), which can oxidize linoleic acid to sporulation hormones.Mn-lipoxygenase belongs to the lipoxygenase gene family. Recombinant Mn-lipoxygenase was successfully expressed in the yeast Pichia pastoris with an expression level of 30 mg/L in fermentor culture. The tentative metal ligands of Mn-lipoxygenase were studied by site-directed mutagenesis. The results show that four residues His-274, His-278, His-462 and the C-terminal Val-602 likely coordinate manganese, as predicted by sequence alignments with Fe lipoxygenases.Mn-lipoxygenase (~100 kDa) contains an Asp-Pro peptide bond in the N-terminal region, which appears to hydrolyze during storage and in the acidic media during Pichia expression to an active enzyme of smaller size, mini-Mn-lipoxygenase (~70 kDa). The active form of Mn-lipoxygenase can oxygenate fatty acids of variable chain length, suggesting that the fatty acids enter the catalytic site with the ω-end (“tail first”).Mn-lipoxygenase is an R-lipoxygenase with a conserved Gly316 residue known as a determinant of stereospecificity in other R/S lipoxygenases. The Gly316Ala mutant showed an increased hydroperoxide isomerase activity and transformed 18:3n-3 and 17:3n-3 to epoxyalcohols.The genome of the rice blast fungus, Magnaporthe grisea, contains putative genes of lipoxygenases and LDS. Mycelia of M. grisea were found to express LDS activity. This enzyme was cloned and sequenced and showed 65% amino acid identity with LDS from G.graminis. Take-all and the rice blast fungi represent a constant threat to staple foods worldwide. Mn-lipoxygenase and LDS might provide new means to combat these pathogens.
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| 2. |
- Hirschberg, Daniel, et al.
(författare)
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Thr94 in bovine myelin basic protein is a second phosphorylation site for 42-kDa mitogen-activated protein kinase (ERK2).
- 2003
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Ingår i: Journal of Protein Chemistry. - : Springer Science and Business Media LLC. - 0277-8033 .- 1573-4943. ; 22:2
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Tidskriftsartikel (refereegranskat)abstract
- Treatment of bovine brain myelin basic protein with 42-kDa mitogen-activated protein kinase [p42 MAPK or extracellular signal-regulated kinase 2 (ERK2)] in the presence of ATP and Mg2+ results in phosphorylation of Thr94 and Thr97. Thr94 is not previously known to be an ERK2 phosphorylation site. Both residues are phosphorylated to about the same extent and are in the highly conserved segment Asn91-Ile-Val-Thr94-Pro-Arg-Thr97-Pro-Pro-Pro-Ser101 MALDI mass spectrometry before and after ERK2 treatment revealed the addition of two phosphate groups to the protein. Tryptic cleavage resulted in a single fragment (positions 91-104) carrying the observed mass increase. Tandem mass spectrometry applied to the tryptic peptide showed that both Thr94 and Thr97 are acceptors of phosphate. A singly phosphorylated species could not be detected. Identification of the ERK2 phosphorylation site Thr94 in bovine myelin basic protein reveals a nontraditional phosphate acceptor position, preceded by three noncharged residues (Asn-Ile-Val). Proline at position -2 or -3 from the phosphorylation site, typical for the recognition sequence of proline-directed kinases, is missing. The results provide information for delineation of a further substrate consensus motif for ERK2 phosphorylation.
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| 3. |
- Mittal, Monica, et al.
(författare)
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Investigation of calcium-dependent activity and conformational dynamics of zebra fish 12-lipoxygenase
- 2017
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Ingår i: Biochimica et Biophysica Acta - General Subjects. - : Elsevier BV. - 0304-4165. ; 1861:8, s. 2099-2111
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Tidskriftsartikel (refereegranskat)abstract
- Background A 12-lipoxygenase in zebra fish (zf12-LOX) was found to be required for normal embryonic development and LOXs are of great interest for targeted drug designing. In this study, we investigate the structural-functional aspects of zf12-LOX in response to calcium. Methods A soluble version of zf12-LOX was created by mutagenesis. Based on multiple sequence alignment, we mutated the putative calcium-responsive amino acids in N-PLAT domain of soluble zf12-LOX. Using a series of biophysical methods, we ascertained the oligomeric state, stability, structural integrity and conformational changes of zf12-LOX in response to calcium. We also compared the biophysical properties of soluble zf12-LOX with the mutant in the absence and presence of calcium. Results Here we provide a detailed characterization of soluble zf12-LOX and the mutant. Both proteins exist as compact monomers in solution, however the enzyme activity of soluble zf12-LOX is significantly increased in presence of calcium. We find that the stimulatory effect of calcium on zf12-LOX is related to a change in protein structure as observed by SAXS, adopting an open-state. In contrast, enzyme with a mutated calcium regulatory site has reduced activity-response to calcium and restricted large re-modeling, suggesting that it retains a closed-state in response to calcium. Taken together, our study suggests that Ca2 +-dependent regulation is associated with different domain conformation(s) that might change the accessibility to substrate-binding site in response to calcium. General significance The study can be broadly implicated in better understanding the mode(s) of action of LOXs, and the enzymes regulated by calcium in general.
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| 4. |
- Mittal, Monica, et al.
(författare)
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Kinetic investigation of human 5-lipoxygenase with arachidonic acid
- 2016
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Ingår i: Bioorganic & Medicinal Chemistry Letters. - : Elsevier. - 0960-894X .- 1464-3405. ; 26:15, s. 3547-3551
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Tidskriftsartikel (refereegranskat)abstract
- Human 5-lipoxygenase (5-LOX) is responsible for the formation of leukotriene (LT)A(4), a pivotal intermediate in the biosynthesis of the leukotrienes, a family of proinflammatory lipid mediators. 5-LOX has thus gained attention as a potential drug target. However, details of the kinetic mechanism of 5-LOX are still obscure. In this Letter, we investigated the kinetic isotope effect (KIE) of 5-LOX with its physiological substrate, arachidonic acid (AA). The observed KIE is 20 +/- 4 on k(cat) and 17 +/- 2 on k(cat)/K-M at 25 degrees C indicating a non-classical reaction mechanism. The observed rates show slight temperature dependence at ambient temperatures ranging from 4 to 35 degrees C. Also, we observed low Arrhenius prefactor ratio (A(H)/A(D) = 0.21) and a small change in activation energy (E-a(D) - E-a(H) = 3.6 J/mol) which suggests that 5-LOX catalysis involves tunneling as a mechanism of H-transfer. The measured KIE for 5-LOX involves a change in regioselectivity in response to deuteration at position C7, resulting in H-abstraction form C10 and formation of 8-HETE. The viscosity experiments influence the (H)k(cat), but not (D)k(cat). However the overall kcat/K-M is not affected for labeled or unlabeled AA, suggesting that either the product release or conformational rearrangement might be involved in dictating kinetics of 5-LOX at saturating conditions. Investigation of available crystal structures suggests the role of active site residues (F421, Q363 and L368) in regulating the donor-acceptor distances, thus affecting H-transfer as well as regiospecificity. In summary, our study shows that that the H-abstraction is the rate limiting step for 5-LOX and that the observed KIE of 5-LOX is masked by a change in regioselectivity.
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| 5. |
- Woolcott, Orison O, et al.
(författare)
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Arachidonic acid is a physiological activator of the ryanodine receptor in pancreatic beta-cells.
- 2006
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Ingår i: Cell Calcium. - : Elsevier BV. - 0143-4160 .- 1532-1991. ; 39:6, s. 529-37
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Tidskriftsartikel (refereegranskat)abstract
- Pancreatic beta-cells have ryanodine receptors but little is known about their physiological regulation. Previous studies have shown that arachidonic acid releases Ca(2+) from intracellular stores in beta-cells but the identity of the channels involved in the Ca(2+) release has not been elucidated. We studied the mechanism by which arachidonic acid induces Ca(2+) concentration changes in pancreatic beta-cells. Cytosolic free Ca(2+) concentration was measured in fura-2-loaded INS-1E cells and in primary beta-cells from Wistar rats. The increase of cytosolic Ca(2+) concentration induced by arachidonic acid (150microM) was due to both Ca(2+) release from intracellular stores and influx of Ca(2+) from extracellular medium. 5,8,11,14-Eicosatetraynoic acid, a non-metabolizable analogue of arachidonic acid, mimicked the effect of arachidonic acid, indicating that arachidonic acid itself mediated Ca(2+) increase. The Ca(2+) release induced by arachidonic acid was from the endoplasmic reticulum since it was blocked by thapsigargin. 2-Aminoethyl diphenylborinate (50microM), which is known to inhibit 1,4,5-inositol-triphosphate-receptors, did not block Ca(2+) release by arachidonic acid. However, ryanodine (100microM), a blocker of ryanodine receptors, abolished the effect of arachidonic acid on Ca(2+) release in both types of cells. These observations indicate that arachidonic acid is a physiological activator of ryanodine receptors in beta-cells.
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| 6. |
- Yektaei-Karin, Elham, et al.
(författare)
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Modulation of leukotriene signaling inhibiting cell growth in chronic myeloid leukemia
- 2017
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Ingår i: Leukemia and Lymphoma. - : Informa UK Limited. - 1042-8194 .- 1029-2403. ; 58:8, s. 1903-1913
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Tidskriftsartikel (refereegranskat)abstract
- Although tyrosine kinase inhibitors (TKIs) have dramatically improved clinical outcome in chronic myeloid leukemia (CML), cure rarely occurs. This may be due to BCR-ABL-independent, aberrant signaling pathways, one of which leads to leukotriene (LT) formation. Well-recognized as inflammatory mediators, LT can also affect oncogenic mechanisms of several tumors. We have previously discovered elevated LT-synthesis and up-regulated cysteinyl-LT-inducing enzyme in CML. Here we report on dose-dependent inhibition of CML cell growth exerted by specific blockers of LT-signaling. Thus, the cysteinyl-LT1-receptor-antagonist montelukast significantly reduced the growth of K562, KCL22, and KU812 cells, as well as primary CD34(+) blood cells from two CML patients. Adding montelukast to the TKI imatinib caused combined inhibition. No effect was seen on normal bone marrow cells. Similarly, growth inhibition was also observed with the 5-lipoxygenase (LO)-inhibitor BWA4C, the 5-LO-activating-protein-(FLAP)-inhibitor licofelone and the LTB4(BLT1)-receptor-antagonist LY293111. Thus, blocking of aberrant LT-signaling may provide an additional, novel therapeutic possibility in CML.
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