Derivatives of thapsigargin as probes of its binding site on endoplasmic reticulum Ca2+ ATPase. Stereoselectivity and important functional groups.
The naturally occurring sesquiterpene lactone thapsigargin is a potent and selective inhibitor of SERCA ATPases, a family of Ca(2+)-pumping ATPases present in the endoplasmic reticulum of all mammalian cells. We have studied some of the molecular features of thapsigargin responsible for its inhibitory action towards these Ca2+ ATPases. A series of thapsigargin analogues were synthesised and their inhibitory potencies determined using the uptake of 45Ca2+ in bovine cerebellar microsomes as a sensitive marker of Ca2+ ATPase activity. An attenuation of the inhibitory potency relative to the parent compound was found ranging from slight to over 3 orders of magnitude. The inhibitory activity showed a very strong configuration dependence, a major contribution from the ester groups at C3 and C10, and an apparently minor contribution from the lactone ring substituents. The data are consistent with thapsigargin fitting to a sterically discriminating cleft involving the hydrophobic transmembrane region of the ATPase, and is compatible with available kinetic evidence of thapsigargin-mediated inhibition.
Christensen
S B
SB
Department of Organic Chemistry, Royal Danish School of Pharmacy, University of Copenhagen, Denmark.
Andersen
A
A
Poulsen
J C
JC
Treiman
M
M
D000818:Animals; D001665:Binding Sites; D000252:Calcium-Transporting ATPases / Q000037:antagonists & inhibitors / Q000378:metabolism*; D002417:Cattle; D004721:Endoplasmic Reticulum / Q000201:enzymology*; D015394:Molecular Structure; D013729:Terpenes / Q000378:metabolism*; D019284:Thapsigargin
D013729:Terpenes; D019284:Thapsigargin; D000252:Calcium-Transporting ATPases