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Ilse Vandecaetsbeek,
Søren Brøgger Christensen, Huizhen Liu,
Paul P Van Veldhoven,
Etienne Waelkens,
Jan Eggermont,
Luc Raeymaekers,
Jesper V Møller,
Poul Nissen,
Frank Wuytack,
Peter Vangheluwe
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ABSTRACT: The ubiquitous sarco(endo)plasmic reticulum (SR/ER) Ca(2+) ATPase (SERCA2b) and secretory-pathway Ca(2+) ATPase (SPCA1a) belong both to the P(2A)-type ATPase subgroup of Ca(2+) transporters and play a crucial role in the Ca(2+) homeostasis of respectively the ER and Golgi apparatus. They are ubiquitously expressed, but their low abundance precludes purification for crystallization. We have developed a new strategy for purification of recombinant hSERCA2b and hSPCA1a that is based on overexpression in yeast followed by a two-step affinity chromatography method biasing towards properly folded protein. In a first step, these proteins were purified with the aid of an analogue of the SERCA inhibitor thapsigargin (Tg) coupled to a matrix. Wild-type (WT) hSERCA2b bound efficiently to the gel, but its elution was hampered by the high affinity of SERCA2b for Tg. Therefore, a mutant was generated carrying minor modifications in the Tg-binding site showing a lower affinity for Tg. In a second step, reactive dye chromatography was performed to further purify and concentrate the properly folded pumps and to exchange the detergent to one more suitable for crystallization. A similar strategy was successfully applied to purify WT SPCA1a. This study shows that it is possible to purify functionally active intracellular Ca(2+) ATPases using successive thapsigargin and reactive dye affinity chromatography for future structural studies. This article is part of a Special Issue entitled: 11th European Symposium on Calcium.
Biochimica et Biophysica Acta 01/2011; 1813(5):1118-27. · 4.66 Impact Factor
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ABSTRACT: Thapsigargin (Tg), a specific inhibitor of sarco/endoplasmic Ca(2+)-ATPases (SERCA), binds with high affinity to the E2 conformation of these ATPases. SERCA inhibition leads to elevated calcium levels in the cytoplasm, which in turn induces apoptosis. We present x-ray crystallographic and intrinsic fluorescence data to show how Tg and chemical analogs of the compound with modified or removed side chains bind to isolated SERCA 1a membranes. This occurs by uptake via the membrane lipid followed by insertion into a resident intramembranous binding site with few adaptative changes. Our binding data indicate that a balanced hydrophobicity and accurate positioning of the side chains, provided by the central guaianolide ring structure, defines a pharmacophore of Tg that governs both high affinity and access to the protein-binding site. Tg analogs substituted with long linkers at O-8 extend from the binding site between transmembrane segments to the putative N-terminal Ca(2+) entry pathway. The long chain analogs provide a rational basis for the localization of the linker, the presence of which is necessary for enabling prostate-specific antigen to cleave peptide-conjugated prodrugs targeting SERCA of cancer cells (Denmeade, S. R., Jakobsen, C. M., Janssen, S., Khan, S. R., Garrett, E. S., Lilja, H., Christensen, S. B., and Isaacs, J. T. (2003) J. Natl. Cancer Inst. 95, 990-1000). Our study demonstrates the usefulness of a simple in vitro system to test and direct development toward the formulation of new Tg derivatives with improved properties for SERCA targeting. Finally, we propose that the Tg binding pocket may be a regulatory site that, for example, is sensitive to cholesterol.
Journal of Biological Chemistry 09/2010; 285(37):28883-92. · 4.77 Impact Factor
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ABSTRACT: Thapsigargin (Tg), a specific inhibitor of sarco/endoplasmic Ca2+-ATPases (SERCA), binds with high affinity to the E2 conformation of these ATPases. SERCA inhibition leads to elevated calcium
levels in the cytoplasm, which in turn induces apoptosis. We present x-ray crystallographic and intrinsic fluorescence data
to show how Tg and chemical analogs of the compound with modified or removed side chains bind to isolated SERCA 1a membranes. This occurs by uptake via the membrane lipid followed by insertion into a resident intramembranous binding site
with few adaptative changes. Our binding data indicate that a balanced hydrophobicity and accurate positioning of the side
chains, provided by the central guaianolide ring structure, defines a pharmacophore of Tg that governs both high affinity
and access to the protein-binding site. Tg analogs substituted with long linkers at O-8 extend from the binding site between
transmembrane segments to the putative N-terminal Ca2+ entry pathway. The long chain analogs provide a rational basis for the localization of the linker, the presence of which
is necessary for enabling prostate-specific antigen to cleave peptide-conjugated prodrugs targeting SERCA of cancer cells
(Denmeade, S. R., Jakobsen, C. M., Janssen, S., Khan, S. R., Garrett, E. S., Lilja, H., Christensen, S. B., and Isaacs, J.
T. (2003) J. Natl. Cancer Inst. 95, 990–1000). Our study demonstrates the usefulness of a simple in vitro system to test and direct development toward the formulation of new Tg derivatives with improved properties for SERCA targeting.
Finally, we propose that the Tg binding pocket may be a regulatory site that, for example, is sensitive to cholesterol.
Journal of Biological Chemistry 09/2010; 285(37):28883-28892. · 4.77 Impact Factor
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ABSTRACT: Removal of each of the acyl groups of thapsigargin at O-3, O-8 and O-10 significant reduces the affinity of the inhibitors to the SERCA1a pump. Replacement of the acyl groups at O-3 and O-10 with flexible residues could be performed with only a minor decrease of the affinity, whereas introduction of voluminous stiff residues caused dramatic reduction of the affinity. The results can be rationalized on the basis of the interactions of thapsigargin with the SERCA1a pump as revealed from 3D X-ray structural models of thapsigargin bound to the SERCA1a. In conclusion the results confirm and elaborate the previously suggested pharmocophore model of thapsigargin.
Bioorganic & medicinal chemistry 08/2010; 18(15):5634-46. · 2.82 Impact Factor
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ABSTRACT: Golgi α-mannosidase II (GMII) is a Family 38 glycosyl hydrolase involved in the eukaryotic N-glycosylation pathway in protein synthesis. Understanding of its catalytic mechanism has been of interest for the development of specific inhibitors that could lead to novel anti-metastatic or anti-inflammatory compounds. The active site of GMII has been characterized by structural studies of the Drosophila homologue (dGMII) and unusually contains a Zn atom which forms contacts with substrate analogues, stabilized catalytic intermediates, and other inhibitors observed in the active site. In this contribution, we analyze the structure of the sugar mimetic compound noeuromycin complexed with dGMII. Distortions of the conformation of this inhibitor, together with similar observations from other complexes, have permitted us to propose specific roles for the Zn atom in the chemical mechanism of catalysis of Family 38 glycosidase. Such insights have relevance to efforts to formulate novel, specific inhibitors of GMII.
07/2009; 24(1-2):55-61.
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ABSTRACT: Four phenylpropanoids and a thapsigargin analogue have been isolated from the fruits of Thapsia garganica. A spectroscopic method for elucidating the relative stereochemistry at the two pairs of stereogenic centers in the phenylpropanoids has been developed. The phenylpropanoids were found to be potent cytotoxins.
Phytochemistry 01/2007; 67(24):2651-8. · 3.35 Impact Factor
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ABSTRACT: The two macrocyclic lipids 2-hydroxymethyl-1,4-dioxacycloicosane-5,20-dione (1) and 3-hydroxy-1,5-dioxacyclohenicosane-6,21-dione (2) have been isolated from the fruits of Thapsia garganica. Tethered lipids are unprecedented in the plant kingdom.
Journal of Natural Products 10/2004; 67(9):1439-40. · 3.13 Impact Factor
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ABSTRACT: The synthesis of isofagomine lactams (2-oxoisofagomines) corresponding to the biologically important hexoses is presented. The D-glucose/D-mannose analogue (3S,4R,5R)-3,4-dihydroxy-5-hydroxymethylpiperidin-2-one (9) was synthesised in 9 steps from D-arabinose, the D-galactose analogue (3S,4S,5R)-3,4-dihydroxy-5-hydroxymethylpiperidin-2-one (10) was synthesised in 11 steps from D-arabinose and the L-fucose analogue (3R,4R,5R)-3,4-dihydroxy-5-methylpiperidin-2-one (11) was synthesised in 12 steps from L-arabinose. The three lactams 9-11 were found to be glycosidase inhibitors with micro- to nanomolar inhibition constants. The lactam 10 showed slow onset inhibition of beta-galactosidase from A. Oryzae. The rate constants for this process were determined to be k(on) = 2.55 x 10(4) M-1 s-1 and k(off) = 1.7 x 10(-3) s-1. The activation energies and standard thermodynamic functions were also determined.
Organic & Biomolecular Chemistry 02/2003; 1(2):282-7. · 3.70 Impact Factor
