Effects of the endosomal lipid bis(monoacylglycero)phosphate on the thermotropic properties of DPPC: A 2H NMR and spin label EPR study

Abstract

Bis(monoacylglycero)phosphate (BMP) is an endosomal lipid with a unique structure that is implicated in the formation of intraendosomal vesicular bodies. Here we have characterized the effects of dioleoyl BMP (BMP18:1) at concentrations of 5, 10, 15 and 20 mol% on the thermotropic behavior of dipalmitoyl phosphatidylcholine (DPPC) vesicles, and compared them to those of equimolar concentrations of dioleoyl phosphatidylglycerol (DOPG), a structural isoform of BMP18:1. Because BMP is found in the acidic environments of the late endosome and intralysosomal vesicles, samples were prepared at pH 4.2 to mimic the pH of the lysosome. Both 2H NMR of perdeuterated DPPC and spin-labeled EPR with 16-Doxyl phosphatidylcholine were utilized in these investigations. NMR and EPR results show that BMP18:1 induces a lowering in the main phase transition temperature of DPPC similar to that of DOPG. The EPR studies reveal that BMP18:1 induced more disorder in the Lβ phase when compared to equimolar concentrations of DOPG. Analysis from dePaked 2H NMR spectra in the Lα phase reveal that BMP18:1 induces less disorder than equal concentrations of DOPG. Additionally, the results demonstrate that BMP mixes with other phospholipids as a phospholipid and not as a detergent molecule as once speculated.

Effect of Lipid Headgroup Charge and pH on the Stability and Membrane Insertion Potential of Calcium Condensed Gene Complexes

“…7,46 More relevant to this study, BMP, an isomer of PG with the same headgroup charge, 48,49 but differences in the position of the glycerol units on the phosphate moiety, is a unique anionic lipid found in significant fractions in the late endosomes. 7,49,50 Since BMP was not stable as a monolayer in our experimental setup because of its high solubility and tendency to form vesicles, 51–53 we chose to use PG headgroups as model lipid system that remains anionic at the pHs relevant to this study, in order to understand the interactions of the CPPs with anionic headgroups that are enriched in the late endosomes. 48–50 …”

“…Zwitterionic phospholipid (POPC) and anionic phospholipids (POPS and POPG) were used as simple mimics of the cell membranes. PC is the most common phospholipid in the cell membrane of eukaryotic cells, whereas anionic PS are normally found in the inner leaflet of the plasma membrane as well as endosomal membranes. ,, Even though PG headgroups are present at 1–2% in the plasma membrane, they have often been used as model anionic lipids to study the function of CPP. , More relevant to this study, BMP, an isomer of PG with the same headgroup charge, , but differences in the position of the glycerol units on the phosphate moiety, is a unique anionic lipid found in significant fractions in the late endosomes. ,, Since BMP was not stable as a monolayer in our experimental setup because of its high solubility and tendency to form vesicles, − we chose to use PG headgroups as model lipid system that remains anionic at the pHs relevant to this study, in order to understand the interactions of the CPPs with anionic headgroups that are enriched in the late endosomes. − …”

β2-Microglobulin Amyloid Fibril-Induced Membrane Disruption Is Enhanced by Endosomal Lipids and Acidic pH

“…Although BMP has been shown to mix with other phospholipids as a lipid, and not to act as a detergent as once speculated [56], [65], incorporation of BMP into zwitterionic lipid bilayers has been shown to induce less disorder in the liquid-crystalline phase, compared with the inclusion of equimolar concentrations of DOPG [65]. Altered disorder in BMP-containing membranes may account for the greater dye release observed upon interaction between β 2 m fibrils and BMP-containing liposomes when compared with POPG-containing LUVs.…”

“…The structure of BMP is unusual from two perspectives; i) it is a phospholipid with two glycerol groups each with a single acyl chain, which results in a cone like shape in the lipid bilayer and ii) it possesses a unique sn- 1 glycerophosphate backbone (typically associated with archeal glycerophospholipids), not the usual sn- 3 stereochemistry of mammalian lipids [64] . Although BMP has been shown to mix with other phospholipids as a lipid, and not to act as a detergent as once speculated [56] , [65] , incorporation of BMP into zwitterionic lipid bilayers has been shown to induce less disorder in the liquid-crystalline phase, compared with the inclusion of equimolar concentrations of DOPG [65] . Altered disorder in BMP-containing membranes may account for the greater dye release observed upon interaction between β 2 m fibrils and BMP-containing liposomes when compared with POPG-containing LUVs.…”

Lipid Sorting and Multivesicular Endosome Biogenesis

“…It has been shown that LBPA has the intrinsic capacity to deform membranes in vitro (Matsuo et al 2004), a situation that probably reflects ILV formation within late endosomes in vivo. However, only the 2,2 0 -LBPA isoform, but not 3,3 0 -LBPA, triggers vesicle formation within acidic liposomes, in a process that is controlled by its partner, the ESCRT-associated protein ALIX (Matsuo et al 2004;Frederick et al 2010). ALIX specificity toward LBPA is conferred by a flexible loop in the Bro1 domain that undergoes a conformational change upon membrane association and requires a calcium atom bound near the lipid interaction site (Bissig et al 2013).…”