Unravelling the orientation of the inositol-biphosphate ring and its dependence on phosphatidylinositol 4,5-bisphosphate cluster formation in model membranes

Hypothesis: Inositol phospholipids are well known to form clusters in the cytoplasmic leaflet of the plasma membrane that are responsible for the interaction and recruitment of proteins involved in key biological processes like endocytosis, ion channel activation and secondary messenger production. Although their phosphorylated inositol ring headgroup plays an important role in protein binding, its ori-entation with respect to the plane of the membrane and its lateral packing density has not been previ-ously described experimentally.Experiments: Here, we study phosphatidylinositol 4,5-bisphosphate (PIP2) planar model membranes in the form of Langmuir monolayers by surface pressure-area isotherms, Brewster angle microscopy and neutron reflectometry to elucidate the relation between lateral (in-plane) and perpendicular (out-of -plane) molecular organization of PIP2.Findings: Different surface areas were explored through monolayer compression, allowing us to correlate the formation of transient PIP2 clusters with the change in orientation of the inositol-biphosphate head -group, which was experimentally determined by neutron reflectometry.(c) 2022 The Author(s). Published by Elsevier Inc.

Automated summary

This study experimentally investigates the molecular organization of phosphatidylinositol 4,5-bisphosphate (PIP2) and reveals its correlation with the formation of transient PIP2 clusters in both lateral and perpendicular directions.