PIP2 Reshapes Membranes through Asymmetric Desorption

Abstract

is an important signaling lipid in eukaryotic cell plasma membranes, playing an essential role in diverse cellular processes. The headgroup of PIP2 is highly negatively charged, and this lipid displays a high critical micellar concentration compared to housekeeping phospholipid analogs. Given the crucial role of PIP2, it is imperative to study its localization, interaction with proteins, and membrane-shaping properties. Biomimetic membranes have served extensively to elucidate structural and functional aspects of cell membranes including protein-lipid and lipid-lipid interactions, as well as membrane mechanics. Incorporation of PIP2 into biomimetic membranes, however, has at times resulted in discrepant findings described in the literature. With the goal to elucidate the mechanical consequences of PIP2 incorporation, we studied the desorption of PIP2 from biomimetic giant unilamellar vesicles by means of a fluorescent marker. A decrease in fluorescence intensity with the age of the vesicles suggested that PIP2 lipids were being desorbed from the outer leaflet of the membrane. To evaluate whether this desorption was asymmetric, the vesicles were systematically diluted. This resulted in an increase in the number of internally tubulated vesicles within minutes after dilution, suggesting that the desorption was asymmetric and also generated membrane curvature. By means of a saturated chain homolog of PIP2, we showed that the fast desorption of PIP2 is facilitated by presence of an arachidonic lipid tail and is possibly due to its oxidation. Through measurements of the pulling force of membrane tethers, we quantified the effect of this asymmetric desorption on the spontaneous membrane curvature. Furthermore, we found that the spontaneous curvature could be modulated by externally increasing the concentration of PIP2 micelles. Given that the local concentration of PIP2 in biological membranes is variable, spontaneous curvature generated by PIP2 may affect the formation of highly curved structures that can serve as initiators for signaling events.

Synaptotagmin-1 C2B domains cooperatively stabilize the fusion stalk via a master-servant mechanism

“…Even with T328E,T329E mutations, the mutant master domain (red lines in panels 6a and 6c) shows good interactions with PIP 2 lipids through both its poly-basic patch and its arginines 398,399, although less frequent than the wild-type master domain (black lines). These results indicate that the main interactions between PIP 2 and master C2B domains (either wild-type or mutant) is the polybasic region 321-332, in line with previous studies describing PIP 2 mediated membrane bending 32,35–37 and fusion 36,38–40 . Additionally, also arginines 398,399 appear to be key during C2B:PIP 2 interactions for both wild-type and mutant master domains, also in agreement with previous data 13 .…”

Membrane Heterogeneity Controls Cellular Endocytic Trafficking

“…For clathrin-dependent endocytosis, heterogeneity mainly results from plasma membrane regions enriched in phosphoinositide 4,5 phosphate [PI(4,5)P 2 ] and displaying high membrane curvature, which together provide the initial impetus for formation of a clathrin coated pit ( Figure 1A). Asymmetric enrichments of PI(4,5)P 2 lead to spontaneous induction of membrane curvature in vitro through a mechanism that remains to be elucidated (Shukla et al, 2019). In turn, membrane curvature leads to recruitment and stabilization of a clathrin-lattice at the plasma membrane ( Figure 1B) (Jost et al, 1998;Cremona et al, 1999).…”

Plasma Membrane MCC/Eisosome Domains Promote Stress Resistance in Fungi

“…These abnormal invaginations required Pil1 for their formation, and they shared a boundary with eisosomes (106). It is significant that the membrane invaginations are enriched in PI(4,5)P 2 , as this lipid can promote formation of curved membranes (107). However, more research needs to be done in this area, as, for example, changes in membrane tension also impact membrane fluidity, which can have broad effects on the organization of PM proteins and lipids.…”