Bis (monoacylglycero) phosphate interfacial properties and lipolysis by pancreatic lipase-related protein 2, an enzyme present in THP-1 human monocytes

The interfacial physical properties of bis(monoacylglycero)phosphate (BMP) and its derivatives with three oleoyl chains (hemi-BDP) and four oleoyl chains (bis(diacylglycero)phosphate, BDP) were investigated using Langmuir monomolecular films. The mean molecular area of BMP at the collapse surface pressure (45 mN m− 1) was similar to those measured with other phospholipids bearing two acyl chains (66 and 59.6 Å2 molecule− 1 at pH 5.5 and 8.0, respectively). In Hemi-BDP and BDP, the mean molecular area increased by 26 and 35 Å2 molecule− 1 per additional acyl chain at pH 5.5 and 8.0, respectively. When BMP was added to a phospholipid mixture mimicking late endosome membrane composition at pH 8.0, the mean phospholipid molecular area increased by 7% regardless of the surface pressure. In contrast, the variation in molecular area was surface pressure-dependent at pH 5.5, a pH value close to that of intra-endosomal content. BMP and hemi-BDP, but not BDP, were hydrolyzed by pancreatic lipase-related protein 2 (PLRP2), which exhibits phospholipase A1 activity. At pH 5.5, the maximum activities of PLRP2 on BMP were recorded at high surface pressures (25–35 mN/m). At pH 8.0, the PLRP2 activity vs. surface pressure showed a bell-shaped curve with maximum activities at 15 mN/m for both BMP and hemi-BDP. This is a new activity for this enzyme which could degrade cellular BMP since both human PLRP2 (HPLRP2) and BMP were localized in human monocytic THP-1 cells. This is the first report on the cellular localization of HPLRP2 in human monocytes.

Research Highlights
► Interfacial properties of bis (monoacylglycero) phosphate (BMP) and mixed monolayers.
► pH-dependent role of BMP in vesicle formation.
► Phospholipase A1 activity of pancreatic lipase related-protein 2 (PLRP2) on BMP.
► Cellular location of human PLRP2 and BMP in THP-1 monocytes.