Abstract
We have monitored the interaction of several lipids with the bovine brain calmodulin(CaM) and analyzed the effect of lysophosphatidycholine (lyso-PC, 2–50 μ g/ml) on conformation of CaM and the interaction between CaM and CaM-binding protein (CaMBP), using a fluorescence signal of 1-(dimethylamino) naphthalene-5-sulfonate-labeled CaM(DNS-CaM). Lyso-PC (egg, 20 μg/ml), among various natural lipids including phosphatidylserine (PS), phosphatidylinositol (PI), phosphatidylethanolamine (PE) and their lyso forms, greatly and dose-dependently enhanced the intensity of DNS fluorescence of DNS-CaM in the presence (100 μ M CaCl 2) and absence (1 mM EGTA) of Ca 2+. Apparent dissociation constants calculated from the fluorometric titrations of binding of lyso-PC to DNS-CaM were 0.6 and 3.7 μg/ml in the presence and absence of Ca 2+, respectively. Lyso-PC remarkably prevented both trypsin-induced quenching of the fluorescence of DNS-CaM and tryptic digestion of native CaM in the absence of Ca 2+. Enhancement of DNS fluorescence of DNS-CaM was CaMBP was observed only in the presence of Ca 2+and lyso-PC could further increase the fluorescence intensity of the complex. These all results suggest that lyso-PC can modulate the interaction between CaM and CaMBP as a result of its direct effect on conformation of CaM.
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