Effects of sphingosine on peripheral membrane interactions: Comparison of adriamycin, cytochrome c, and phospholipase A2

Abstract

As revealed by resonance energy transfer utilizing pyrene-labeled phosphatidylcholine donor, the mainly electrostatically controlled binding of adriamycin (Adr) and cytochrome c (cyt c) to mixed egg yolk phosphatidic acid/phosphatidylcholine (eggPA/eggPC, 15:85 molar ratio) liposomes was reversed upon the inclusion of increasing contents of sphingosine. At a [sphingosine]/[eggPA] molar ratio of approximately 2:1, the degree of fluorescence quenching by cyt c and Adr was approximately the same as when using liposomes lacking eggPA. Similarly, the increase in the surface pressure of sphingosine/eggPA monolayers on an air/water interface due to the membrane penetration of either cyt c or Adr was progressively reduced by increasing the content of sphingosine in the monolayers. The above critical [sphingosine]/[acidic phospholipid] stoichiometry yielding dissociation of the positively charged ligands Adr or cyt c from membrane acidic phospholipids was shifted from 2:1 to 1:1 upon substituting egg phosphatidylglycerol (eggPG) for eggPA. Accordingly, charge neutralization of the acidic phospholipids by sphingosine could be involved. One eggPA (having maximally two negative charges) appears to require two molecules of sphingosine whereas the maximally singly charged eggPG is neutralized by one sphingosine. For comparison we also studied the effects of sphingosine on the phospholipase A2 catalyzed hydrolysis of the pyrene-labeled acidic alkylacyl phospholipid analog 1-octacosanyl-2-[6-(pyren-1-yl)]hexanoyl-sn-glycero-3- phosphatidylmethanol (C28-O-PHPM) and the corresponding phosphatidylcholine (C28-O-PHPC). In the presence of low Ca2+ concentrations (approximately 50 nM) limiting the rate of the enzymatic reaction, sphingosine gradually inhibited the hydrolysis of phosphatidylcholine, and at 1:6 sphingosine/C28-O-PHPC a nearly complete lack of hydrolysis was evident.(ABSTRACT TRUNCATED AT 250 WORDS)

Electrochemical cues regulate assembly of the Frizzled/Dishevelled complex at the plasma membrane during planar epithelial polarization

“…4m–r; it did not affect LactC2 membrane localization, Supplementary Information, Fig. S2c)19,17. In contrast, sphingosine treatment allowed effective association of the DshKR/E mutant with Fz at the membrane, suggesting that the neutralization of surface charge rescues repulsion of the DshKR/E mutant from the membrane (Fig.…”

Effect of sphingosine on domain morphology in giant vesicles

“…Various studies suggest that the cellular functions of SPH are exerted more through its influence on the lipid phase behavior than its direct interaction with proteins [19,40,41]. The aim of our study was to examine the effect of SPH on domain morphology and its interactions with the raft-forming lipids, CHOL and SM.…”

Membranes: a meeting point for lipids, proteins and therapies

“…It is also worth noticing that electrostatics in biomembranes is, in general, dominated by the above negatively charged lipids. Yet, also cationic lipids are found, the most abundant being sphingosine [84] and studies with model membranes have shown its association with acidic phospholipids to regulate peripheral lipid–protein as well as lipid–small molecule interactions [85]. More detailed studies on model membranes have demonstrated the interplay of surface charge density and the dissociation behaviour of the acidic phospholipid headgroup to exert a pronounced impact on lipid–protein interactions evident as distinctly different binding modes of cytochrome c to protonated and deprotonated phospholipid [86, 87].…”