Does actin bind to membrane lipids under conditions compatible with those existing in vivo?
Using an in vitro system composed of liposomes and pure actin, we previously established that actin can interact directly with membrane lipids and suggested that this interaction may also exist in vivo. However, an important potential caveat has been brought to our attention concerning the high concentrations of lipids used in our assays. Indeed, it has been hypothesized that under our experimental conditions, divalent cations may become tightly bound to the lipid bilayers, reducing the free divalent cation concentration to non-physiological levels. The observed actin-lipid interaction has therefore been suggested to be an in vitro artifact. In order to test this hypothesis, we have measured the capture of Mg++ by DSPC liposomes under our experimental conditions. Our results show that only one Mg++ ion is captured for every 40 DSPC molecules. The resulting reduction in the free Mg++ concentration is therefore negligible in our assays. It is concluded that the actin-lipid interaction which we have previously documented indeed occurs under ionic conditions compatible with those found in vivo.
Gicquaud
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Département de chimie-biologie Université du Québec à Trois-Rivières, Canada.
D000199:Actins / Q000378:metabolism* / Q000648:ultrastructure*; D007700:Kinetics; D008051:Lipid Bilayers; D008081:Liposomes; D008274:Magnesium / Q000494:pharmacology; D008854:Microscopy, Electron; D010713:Phosphatidylcholines
D000199:Actins; D008051:Lipid Bilayers; D008081:Liposomes; D010713:Phosphatidylcholines; C010942:1,2-distearoyllecithin; D008274:Magnesium