scholarly journals Affinity of okadaic acid to type-1 and type-2A protein phosphatases is markedly reduced by oxidation of its 27-hydroxyl group

1994 ◽  
Vol 298 (2) ◽  
pp. 259-262 ◽  
Author(s):  
K Sasaki ◽  
M Murata ◽  
T Yasumoto ◽  
G Mieskes ◽  
A Takai
Keyword(s):  
Okadaic Acid ◽  
Dissociation Constants ◽  
Protein Phosphatases ◽  
Three Dimensional ◽  
Inhibitory Effect ◽  
Hydroxyl Group ◽  
Hydroxyl Groups ◽  
Intramolecular Bonding ◽  
Free Energy Of Binding

Okadaic acid (OA), a potent inhibitor of type-1 and type-2A protein phosphatases (PP1 and PP2A), has four hydroxyl groups at 2, 7, 24 and 27 positions (see Figure 1). By chemical treatment of OA we synthesized a derivative, in which the 27-hydroxyl group was specifically oxidized (27-dehydro-OA). The inhibitory effect of this OA derivative was examined on the activities of PP1 and PP2A, which were inhibited by intact OA with dissociation constants (Ki) of 150 nM and 32 pM respectively. We found that the affinity of OA was decreased 40-fold (Ki = 6 microM) with PP1 and 230-fold (Ki = 7.3 nM) with PP2A after oxidation of the 27-hydroxyl group. According to the model of the three-dimensional conformation of OA on the basis of X-ray analyses, the 27-hydroxyl group appears to be present in a position relatively free from intramolecular bonding formation, in comparison with the other three hydroxyl groups. The marked increases in the Ki values for PP1 and PP2A, which indicate the reduction of the absolute values of the free energy of binding by 9 kJ/mol and 14 kJ/mol respectively, may imply that the 27-hydroxyl group serves as a binding site with the phosphatase molecules.

scholarly journals Inhibitory effect of okadaic acid derivatives on protein phosphatases. A study on structure-affinity relationship

1992 ◽  
Vol 284 (2) ◽  
pp. 539-544 ◽  
Author(s):  
A Takai ◽  
M Murata ◽  
K Torigoe ◽  
M Isobe ◽  
G Mieskes ◽  
...  
Keyword(s):  
Okadaic Acid ◽  
Structural Changes ◽  
Protein Phosphatases ◽  
Inhibitory Effect ◽  
Chemical Processes ◽  
Hydroxyl Group ◽  
Confidence Limits ◽  
X Ray ◽  
Structural Modifications

The effect of structural modifications of okadaic acid (OA), a polyether C38 fatty acid, was studied on its inhibitory activity toward type 1 and type 2A protein phosphatases (PP1 and PP2A) by using OA derivatives obtained either by isolation from natural sources or by chemical processes. The dissociation constant (Ki) for the interaction of OA with PP2A was estimated to be 30 (26-33) nM [median (95% confidence limits)]. The OA derivatives used and their affinity for PP2A, expressed as Ki (in brackets) were as follows: 35-methyl-OA (DTX1) [19 (12-25) pM], OA-9,10-episulphide (acanthifolicin) [47 (25-60) pM], 7-deoxy-OA [69 (31-138) pM], 14,15-dihydro-OA [315 (275-360) pM], 2-deoxy-OA [899 (763-1044) pM], 7-O-palmitoyl-OA [greater than 100 nM], 7-O-palmitoyl-DTX1 [greater than 100 nM], methyl okadate [much greater than 100 nM], 2-oxo-decarboxy-OA [much greater than 100 nM] and the C-15-C-38 fragment of OA [much greater than 100 nM]. The sequence of the affinity of these derivatives for PP1 was essentially the same as that observed with PP2A, although the absolute values of Ki were very different for the enzymes. The inhibitory effect of OA on PP2A was reversed by applying a murine monoclonal antibody against OA, which recognizes modifications of the 7-hydroxyl group of the OA molecule. It has been shown by n.m.r. spectroscopy and X-ray analysis that one end (C-1-C-24) of the OA molecule assumes a circular conformation. The present results suggest the importance of the conformation for the inhibitory action of OA on the protein phosphatases. The ratios of the Ki values for PP1 to that for PP2A, which were within the range 10(3)-10(4), tended to be smaller for the derivatives with lower affinity, indicating that the structural changes in OA impaired the affinity for PP2A more strongly than that for PP1.

scholarly journals Inhibitory effect of okadaic acid on the p-nitrophenyl phosphate phosphatase activity of protein phosphatases

1991 ◽  
Vol 275 (1) ◽  
pp. 233-239 ◽  
Author(s):  
A Takai ◽  
G Mieskes
Keyword(s):  
Phosphatase Activity ◽  
Okadaic Acid ◽  
Protein Phosphatase ◽  
Protein Phosphatases ◽  
Inhibitory Effect ◽  
Enzyme Concentration ◽  
Alkaline Phosphatases ◽  
Nitrophenyl Phosphate ◽  
Type 1 Phosphatase

The phosphatase activities of type 2A, type 1 and type 2C protein phosphatase preparations were measured against p-nitrophenyl phosphate (pNPP), a commonly used substrate for alkaline phosphatases. Of the three types of phosphatase examined, the type 2A phosphatase exhibited an especially high pNPP phosphatase activity (119 +/- 8 mumol/min per mg of protein; n = 4). This activity was strongly inhibited by pico- to nano-molar concentrations of okadaic acid, a potent inhibitor of type 2A and type 1 protein phosphatases that has been shown to have no effect on alkaline phosphatases. The dose-inhibition relationship was markedly shifted to the right and became steeper by increasing the concentration of the enzyme, as predicted by the kinetic theory for tightly binding inhibitors. The enzyme concentration estimated by titration with okadaic acid agreed well with that calculated from the protein content and the molecular mass for type 2A phosphatase. These results strongly support the idea that the pNPP phosphatase activity is intrinsic to type 2A protein phosphatase and is not due to contamination by alkaline phosphatases. pNPP was also dephosphorylated, but at much lower rates, by type 1 phosphatase (6.4 +/- 8 nmol/min per mg of protein; n = 4) and type 2C phosphatase (1.2 +/- 3 nmol/min per mg of protein; n = 4). The pNPP phosphatase activity of the type 1 phosphatase preparation shows a susceptibility to okadaic acid similar to that of its protein phosphatase activity, whereas it was interestingly very resistant to inhibitor 2, an endogenous inhibitory factor of type 1 protein phosphatase. The pNPP phosphatase activity of type 2C phosphatase preparation was not affected by up to 10 microM-okadaic acid.

scholarly journals Inhibitory effect of a marine-sponge toxin, okadaic acid, on protein phosphatases. Specificity and kinetics

1988 ◽  
Vol 256 (1) ◽  
pp. 283-290 ◽  
Author(s):  
C Bialojan ◽  
A Takai
Keyword(s):  
Phosphatase Activity ◽  
Okadaic Acid ◽  
Marine Sponge ◽  
Protein Phosphatases ◽  
Kinetic Studies ◽  
High Specificity ◽  
Inhibitory Effect ◽  
Acid Type ◽  
Nitrophenyl Phosphate

The inhibitory effect of a marine-sponge toxin, okadaic acid, was examined on type 1, type 2A, type 2B and type 2C protein phosphatases as well as on a polycation-modulated (PCM) phosphatase. Of the protein phosphatases examined, the catalytic subunit of type 2A phosphatase from rabbit skeletal muscle was most potently inhibited. For the phosphorylated myosin light-chain (PMLC) phosphatase activity of the enzyme, the concentration of okadaic acid required to obtain 50% inhibition (ID50) was about 1 nM. The PMLC phosphatase activities of type 1 and PCM phosphatase were also strongly inhibited (ID50 0.1-0.5 microM). The PMCL phosphatase activity of type 2B phosphatase (calcineurin) was inhibited to a lesser extent (ID50 4-5 microM). Similar results were obtained for the phosphorylase a phosphatase activity of type 1 and PCM phosphatases and for the p-nitrophenyl phosphate phosphatase activity of calcineurin. The following phosphatases were not affected by up to 10 microM-okadaic acid: type 2C phosphatase, phosphotyrosyl phosphatase, inositol 1,4,5-trisphosphate phosphatase, acid phosphatases and alkaline phosphatases. Thus okadaic acid had a relatively high specificity for type 2A, type 1 and PCM phosphatases. Kinetic studies showed that okadaic acid acts as a non-competitive or mixed inhibitor on the okadaic acid-sensitive enzymes.

Pleiotropic effect of okadaic acid on maturing mouse oocytes

Development ◽  
1991 ◽  
Vol 112 (4) ◽  
pp. 971-980 ◽  
Author(s):  
H. Alexandre ◽  
A. Van Cauwenberge ◽  
Y. Tsukitani ◽  
J. Mulnard
Keyword(s):  
Protein Kinase ◽  
Okadaic Acid ◽  
Protein Phosphatases ◽  
Chromatin Condensation ◽  
Polar Body ◽  
Germinal Vesicle ◽  
Inhibitory Effect ◽  
Negative Control ◽  
Germinal Vesicle Breakdown ◽  
Mouse Oocytes

Okadaic acid (OA), a potent inhibitor of types 1 and 2A protein phosphatases, was shown recently to induce chromatin condensation and germinal vesicle breakdown (GVBD) in mouse oocytes arrested at the dictyate stage by dibutyryl cAMP (dbcAMP), isobutyl methylxanthine (IBMX) and 12,13-phorbol dibutyrate (PDBu). We confirm these results using IBMX and another phorbol diester, 12-O-tetradecanoylphorbol-13-acetate (TPA) and show that OA also bypasses the inhibitory effect of 6-dimethylaminopurine (6-DMAP). It has been concluded that protein phosphatases 1 and/or 2A (PP1, 2A), involved in the negative control of MPF activation, are thus operating downstream from both the protein kinase A and protein kinase C catalysed phosphorylation steps that prevent the breakdown of GV. Similar enzymatic activities are also able to counteract the general inhibition of protein phosphorylation. However, PP1 and/or PP2A are positively involved in the activation of pericentriolar material (PCM) into microtubule organizing centres (MTOCs). This explains the inhibitory effect of OA on spindle assembly. Finally, OA interferes with the integrity and/or function of actomyosin filaments. This results in a dramatic ruffling of the plasma membrane leading to the internalization of large vacuoles, the inhibition of chromosome centrifugal displacement and, consequently, the prevention of polar body extrusion.

scholarly journals Involvement of protein phosphatases 1 and 2A in the control of M phase-promoting factor activity in starfish.

1989 ◽  
Vol 109 (6) ◽  
pp. 3347-3354 ◽  
Author(s):  
A Picard ◽  
J P Capony ◽  
D L Brautigan ◽  
M Dorée
Keyword(s):  
Okadaic Acid ◽  
Protein Phosphatases ◽  
Germinal Vesicle ◽  
Histone H1 ◽  
Specific Inhibition ◽  
Factor Activity ◽  
Microtubule Network ◽  
Germinal Vesicle Breakdown ◽  
M Phase

Specific inhibition of types 1 and 2A protein phosphatases by microinjection of okadaic acid (OA) into starfish oocytes induced germinal vesicle breakdown and activation of M phase-promoting factor (MPF) and histone H1 kinase. The effects were evident in immature oocytes arrested at first meiotic prophase as well as in fully mature oocytes arrested at the pronucleus stage. In addition, MPF and histone H1 kinase were stabilized for several hours and protected from inactivation by inhibition of type 1 protein phosphatases with either OA or specific anti-phosphatase antibodies. Microinjection of okadaic acid was associated with unusual changes of the microtubule network, including the disappearance of spindles and extension of the cytoplasmic array of microtubules. MPF activation after OA injection was associated with dephosphorylation of phosphothreonine and phosphoserine residues in cdc2, showing that neither type 1 nor 2A protein phosphatases catalyzes these dephosphorylations. The effects of OA on MPF activation and inactivation appeared to involve the cyclin subunit. OA did not induce MPF activation in the absence of protein synthesis and it prevented degradation of cyclin. Therefore protein phosphatases types 1 and 2A appear to be involved in activation and inactivation of MPF involving mechanisms that operate after cyclin synthesis and before its degradation.

Crystal structure of antimony oxalate hydroxide, Sb(C2O4)OH

2010 ◽  
Vol 25 (1) ◽  
pp. 19-24 ◽  
Author(s):  
James A. Kaduk ◽  
Mark A. Toft ◽  
Joseph T. Golab
Keyword(s):  
Crystal Structure ◽  
Hydrogen Bonds ◽  
Rietveld Method ◽  
Three Dimensional ◽  
Hydroxyl Group ◽  
Hydroxyl Groups ◽  
X Ray ◽  
Oxalate Anion ◽  
Fourier Techniques ◽  
Difference Fourier

The crystal structure of Sb(C2O4)OH has been solved by charge flipping in combination with difference Fourier techniques using laboratory X-ray powder data exhibiting significant preferred orientation and refined by the Rietveld method. The compound crystallizes in Pnma with a=5.827 13(3), b=11.294 48 (10), c=6.313 77(3) Å, V=415.537(5) Å3, and Z=4. The crystal structure contains pentagonal pyramidal Sb3+ cations, which are bridged by hydroxyl groups to form zigzag chains along the a axis. Each oxalate anion chelates to two Sb in approximately the ab plane, linking the chains into a three-dimensional framework. The H of the hydroxyl group is probably disordered in order to form stronger more-linear hydrogen bonds. The highest energy occupied molecular orbitals are the Sb3+ lone pairs. The structure is chemically reasonable compared to other antimony oxalates and to Bi(C2O4)OH.

scholarly journals Serine 124 completes the Tyr, Lys and Ser triad responsible for the catalysis of human type 1 3beta-hydroxysteroid dehydrogenase

2004 ◽  
Vol 33 (1) ◽  
pp. 253-261 ◽  
Author(s):  
JL Thomas ◽  
WL Duax ◽  
A Addlagatta ◽  
LA Scaccia ◽  
KA Frizzell ◽  
...  
Keyword(s):  
Catalytic Domain ◽  
Three Dimensional ◽  
Homology Model ◽  
Hydroxysteroid Dehydrogenase ◽  
Catalytic Triad ◽  
Hydroxyl Group ◽  
Wild Type ◽  
Cofactor Binding ◽  
Human Type

Human 3beta-hydroxysteroid dehydrogenase/isomerase (3beta-HSD) is a key steroidogenic enzyme that catalyzes the first step in the conversion of circulating dehydroepiandrosterone (DHEA), pregnenolone or 17alpha-hydroxypregenolone to produce the appropriate, active steroid hormone(s): estradiol, testosterone, progesterone, aldosterone or cortisol respectively. Our mutagenesis studies have identified Tyr154 and Lys158 as catalytic residues for the 3beta-HSD reaction. Our three-dimensional homology model of 3beta-HSD shows that Tyr154 and Lys158 are oriented near the 3beta-hydroxyl group of the bound substrate steroid, and predicts that Ser123 or Ser124 completes a Tyr-Lys-Ser catalytic triad that operates in many other dehydrogenases. The S123A and S124A mutants of human type 1 3beta-hydroxysteroid dehydrogenase/isomerase (3beta-HSD1) were created by PCR-based mutagenesis, expressed in insect cells using baculovirus and purified to homogeneity. The S124A mutant exhibits no 3beta-HSD activity and has a K(m) value (83.6 microM) for the isomerase substrate that is threefold greater than that of wild-type 1 isomerase. In contrast, S123A has substantial 3beta-HSD activity (DHEA K(m)=11.2 microM; k(cat)=0.8 min(-1)) and utilizes isomerase substrate, 5-androstene-3,17-dione, with a K(m) value (27.6 microM) that is almost identical to wild-type. The K(m) value (4.3 microM) of S124A for NADH as an allosteric activator of isomerase is similar to that of the wild-type 1 enzyme, indicating that Ser124 is not involved in cofactor binding. S123A utilizes NAD as a cofactor for 3beta-HSD and NADH as the activator for isomerase with K(m) values that are similar to wild-type. The 3beta-HSD activities of S123A and wild-type 3beta-HSD increase by 2.7-fold when the pH is raised from 7.4 to the optimal pH 9.7, but S124A exhibits very low residual 3beta-HSD activity that is pH-independent.These kinetic analyses strongly suggest that the Ser124 residue completes the catalytic triad for the 3beta-HSD activity. Since there are 29 Ser residues in the primary structure of human 3beta-HSD1, our homology model of the catalytic domain has been validated by this accurate prediction. A role for Ser124 in the binding of the isomerase substrate, which is the 3beta-HSD product-steroid of the bifunctional enzyme protein, is also suggested. These observations further characterize the structure/function relationships of human 3beta-HSD and bring us closer to the goal of selectively inhibiting the type 1 enzyme in placenta to control the timing of labor or in hormone-sensitive breast tumors to slow their growth.

scholarly journals Role for protein phosphatases in the cell-cycle-regulated phosphorylation of stathmin

1998 ◽  
Vol 334 (1) ◽  
pp. 23-29 ◽  
Author(s):  
Sucharita J. MISTRY ◽  
Heng-Chun LI ◽  
George F. ATWEH
Keyword(s):  
Cell Cycle ◽  
Okadaic Acid ◽  
Protein Phosphatase ◽  
Protein Phosphatases ◽  
Specific Protein ◽  
G1 Phase ◽  
Major Increase ◽  
Protein Phosphatase Type

Stathmin is a major cytosolic phosphoprotein that regulates microtubule dynamics during the assembly of the mitotic spindle. The activity of stathmin itself is regulated by changes in its state of phosphorylation during the transition from interphase to metaphase. For a better understanding of the regulation of stathmin activity during the cell cycle, we explored the mechanism(s) responsible for the decrease in the level of phosphorylation of stathmin as cells complete mitosis and enter a new G1 phase. We show that stathmin mRNA and protein are expressed constitutively throughout the different phases of the cell cycle. This suggests that the non-phosphorylated stathmin that predominates during G1 is not generated by degradation of phosphorylated stathmin in mitosis and synthesis of new unphosphorylated stathmin as cells enter a new G1 phase. This suggested that protein phosphatases might be responsible for dephosphorylating stathmin as cells enter a new cell cycle. Okadaic acid-mediated inhibition of protein phosphatases in vivoshowed a major increase in the level of phosphorylation of stathmin. Dephosphorylation studies in vitro showed differential patterns of site-specific dephosphorylaton of stathmin to protein phosphatase type 1, protein phosphatase type 2A and protein phosphatase type 2B. Thus stathmin might be a target for okadaic acid-sensitive protein phosphatase(s), and its activity in eukaryotic cells might be modulated by the sequential activity of specific protein kinases and phosphatases.

scholarly journals Identification of high levels of type 1 and type 2A protein phosphatases in higher plants

1989 ◽  
Vol 262 (1) ◽  
pp. 335-339 ◽  
Author(s):  
C MacKintosh ◽  
P Cohen
Keyword(s):  
Phosphatase Activity ◽  
Okadaic Acid ◽  
Higher Plants ◽  
Protein Phosphatases ◽  
Phosphorylase Kinase ◽  
Rabbit Muscle ◽  
Plant Type ◽  
Mammalian Tissues ◽  
Type 1 Phosphatase

Extracts of Brassica napus (oilseed rape) seeds contain type 1 and type 2A protein phosphatases whose properties are indistinguishable from the corresponding enzymes in mammalian tissues. The type 1 activity dephosphorylated the beta-subunit of phosphorylase kinase selectively and was inhibited by the same concentrations of okadaic acid [IC50 (concentration causing 50% inhibition) approximately 10 nM], mammalian inhibitor 1 (IC50 = 0.6 nM) and mammalian inhibitor 2 (IC50 = 2.0 nM) as the rabbit muscle type 1 phosphatase. The plant type 2A activity dephosphorylated the alpha-subunit of phosphorylase kinase preferentially, was exquisitely sensitive to okadaic acid (IC50 approximately 0.1 nM), and was unaffected by inhibitors 1 and 2. As in mammalian tissues, a substantial proportion of plant type 1 phosphatase activity (40%) was particulate, whereas plant type 2A phosphatase was cytosolic. The specific activities of the plant type 1 and type 2A phosphatases were as high as in mammalian tissue extracts, but no type 2B or type 2C phosphatase activity was detected. The results demonstrate that the improved procedure for identifying and quantifying protein phosphatases in animal cells is applicable to higher plants, and suggests that okadaic acid may provide a new method for identifying plant enzymes that are regulated by reversible phosphorylation.

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