Inhibition of the Ca2+-ATPase by sesquiterpene lactones

Wictome, M; Ap, Starling; Rp, Sharma; Jm, East; Ag, Lee

doi:10.1042/bst021348s

Cited by 4 publications

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“…The sesquiterpene lactone inhibitors, 2,5-di-íerf-butyl-1,4-benzohydroquinone, and nonylphenol also decrease the equilibrium constant for phosphorylation by P¡ but decrease the El f± E2 equilibrium constant (Michelangeli et al, 1990b;Wictome et al, 1992a,b). The inhibitors all contain -OH groups which appear to be important for activity: 2,5-di-íerí-butyl-1,4-benzoquinone is not an inhibitor of the ATPase, and similarly desoxytrilobolide has no effect on the ATPase, whereas trilobolide is a strong inhibitor (Wictome et al, 1993). Distinct strictural features therefore seem to be involved in stimulation and inhibition of the ATPase.…”

Section: Discussionmentioning

confidence: 99%

Mechanism of Stimulation of the Calcium Adenosinetriphosphatase by Jasmone

Starling¹,

Hughes²,

East³

et al. 1994

Biochemistry

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The ATPase activity of the Ca(2+)-ATPase of skeletal muscle sarcoplasmic reticulum is increased ca. 3-fold at 25 degrees C and pH 7.2 by jasmone at a concentration of 100 microM, concentrations above 10 mM resulting in reduced stimulation. Stimulation by methyl jasmonate, menthol, or menthone requires much higher concentrations. Effects of jasmone are much less marked at 37 degrees C than at 25 degrees C, and much higher concentrations of jasmone are required to stimulate ATPase activity at pH 6.0 than at pH 7.2. The effects of jasmone on the ATPase are highly specific. Jasmone has no effect on the E1<-->E2 equilibrium constant for the ATPase or on Ca2+ binding. The rate of phosphorylation by ATP is unaffected by jasmone, and only small effects are seen on the reaction of the phosphorylated ATPase with ADP. Jasmone does, however, increase the rate of dephosphorylation by a factor of 2 and the rate of dissociation of Ca2+ from the phosphorylated ATPase by a factor of 3. Jasmone decreases the level of phosphorylation of the ATPase by P(i) in the absence of Ca2+ consistent with a decrease in the equilibrium constant E2P(i)Mg<-->E2PMg. Reconstitution of the ATPase with dimyristoleoylphosphatidylcholine decreases the stoichiometry of Ca2+ binding from the usual 2:1 to 1:1. Unlike other hydrophobic molecules, jasmone failed to reverse this effect. Further, jasmone had very similar effects on the activity of the ATPase reconstituted with either dimyristoleoylphosphatidylcholine or dioleoylphosphatidylcholine, whereas other hydrophobic molecules caused a much greater stimulation of activity for the ATPase reconstituted with the short-chain lipid.

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Section: Discussionmentioning

confidence: 99%

Mechanism of Stimulation of the Calcium Adenosinetriphosphatase by Jasmone

Starling¹,

Hughes²,

East³

et al. 1994

Biochemistry

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“…The Ca# + -ATPase is inhibited by a variety of hydrophobic molecules, including sesquiterpene lactones such as thapsigargin and trilobolide and simple hydroxy-containing molecules such as dihydroxybenzene [113][114][115][116][117]. The presence of hydroxy groups has been shown to be important in both sets of inhibitors [118].…”

Section: Control Of the Ca 2 + -Atpasementioning

confidence: 99%

What the structure of a calcium pump tells us about its mechanism

2001

Biochem. J.

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The report of the crystal structure of the Ca(2+)-ATPase of skeletal muscle sarcoplasmic reticulum in its Ca(2+)-bound form [Toyoshima, Nakasako and Ogawa (2000) Nature (London) 405, 647-655] provides an opportunity to interpret much kinetic and mutagenic data on the ATPase in structural terms. There are no large channels leading from the cytoplasmic surface to the pair of high-affinity Ca(2+) binding sites within the transmembrane region. One possible access pathway involves the charged residues in transmembrane alpha-helix M1, with a Ca(2+) ion passing through the first site to reach the second site. The Ca(2+)-ATPase also contains a pair of binding sites for Ca(2+) that are exposed to the lumen. In the four-site model for transport, phosphorylation of the ATPase leads to transfer of the two bound Ca(2+) ions from the cytoplasmic to the lumenal pair of sites. In the alternating four-site model for transport, phosphorylation leads to release of the bound Ca(2+) ions directly from the cytoplasmic pair of sites, linked to closure of the pair of lumenal binding sites. The lumenal pair of sites could involve a cluster of conserved acidic residues in the loop between M1 and M2. Since there is no obvious pathway from the high-affinity sites to the lumenal surface of the membrane, transport of Ca(2+) ions must involve a significant change in the packing of the transmembrane alpha-helices. The link between the phosphorylation domain and the pair of high-affinity Ca(2+) binding sites is probably provided by two small helices, P1 and P2, in the phosphorylation domain, which contact the loop between transmembrane alpha-helices M6 and M7.

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“…The sesquiterpene lactones thapsigargin [2,3,17,21,35], trilobolide [8,9] and TvA [8] are potent inhibitors of the Ca2+-ATPase with affinities in the nanomolar range [11]. The stoichiometry of binding is 1:1, either with respect to total protein or with respect to 'functional' ATPase (as defined by the maximum level of phosphoenzyme formation obtained with ATP), depending on the preparation of the ATPase [2][3][4]12].…”

Section: Discussionmentioning

confidence: 99%

“…Sesquiterpene lactones related to thapsigargin are specific inhibitors of the Ca2+-ATPase of sarcoplasmic reticulum (SR) and of endoplasmic reticulum, with no effects on the Ca21-ATPase of the plasma membrane or on other P-type ATPases [1][2][3][4][5]. Members of this class of inhibitor include thapsigargin itself and thapsigargicin, both isolated from Thapsia garganica [6], thapsivillosin A (TvA) isolated from Thapsia villosa [7][8][9] and trilobolide, extracted from Laser trilobum [9,10] (for structures, see insert to Figure 1). The inhibitors are of high affinity, e.g.…”

Section: Introductionmentioning

confidence: 99%

Binding of sesquiterpene lactone inhibitors to the Ca2+-ATPase

Wictome

Khan

East

et al. 1995

Biochemical Journal

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The mechanism of inhibition of the Ca(2+)-ATPase from sarcoplasmic reticulum by the sesquiterpene lactones thapsigargin, trilobolide and thapsivillosin A (TvA) has been determined. A decrease in the affinity of the ATPase for Ca2+ is observed in the presence of the inhibitors (I), consistent with a shift in the E1/E2 equilibrium for the ATPase towards E2 forms. Amounts of inhibitor beyond a 1:1 molar ratio with ATPase produce no further decrease in affinity for Ca2+, inconsistent with the formation of a dead-end complex. Measurements of the rate of quenching of the tryptophan fluorescence of the ATPase by TvA are consistent with an association step to give E2I followed by an isomerization to a modified state E2AI. The kinetics of the reversal of the effects of TvA by Ca2+ at sub-stoichiometric amounts of TvA are bi-exponential, with a fast component whose rate is independent of TvA concentration and equal to the rate observed in the absence of TvA, and a slow component whose rate decreases with increasing TvA concentration. These observations are also consistent with the formation of a modified state E2AI following the initial binding of I to E2. The equilibrium constant E2AI/E2I increases in the order TvA < trilobolide < thapsigargin. The results suggest that the effects of the inhibitors on the overall ratio of E2 to E1 forms of the ATPase follow largely from the formation of E2AI from E2I, and that binding constants are very similar for E1Ca2, E1 and E2.

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Inhibition of the Ca2+-ATPase by sesquiterpene lactones

Cited by 4 publications

References 0 publications

Mechanism of Stimulation of the Calcium Adenosinetriphosphatase by Jasmone

Mechanism of Stimulation of the Calcium Adenosinetriphosphatase by Jasmone

What the structure of a calcium pump tells us about its mechanism

Binding of sesquiterpene lactone inhibitors to the Ca2+-ATPase

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