Live cell imaging with protein domains capable of recognizing phosphatidylinositol 4,5-bisphosphate; a comparative study
TL;DR: A comparative analysis of several recently-described yeast PH domains as well as the mammalian Tubby domain showed that both the PLCδ1PH-GFP and the GFP-Tubby domain are useful reporters of PtdIns(4,5)P2 changes in the plasma membrane, with distinct advantages and disadvantages.
Abstract: Phosphatidylinositol 4,5-bisphosphate [PtdIns(4,5)P2] is a critically important regulatory phospholipid found in the plasma membrane of all eukaryotic cells. In addition to being a precursor of important second messengers, PtdIns(4,5)P2 also regulates ion channels and transporters and serves the endocytic machinery by recruiting clathrin adaptor proteins. Visualization of the localization and dynamic changes in PtdIns(4,5)P2 levels in living cells is critical to understanding the biology of PtdIns(4,5)P2. This has been mostly achieved with the use of the pleckstrin homology (PH) domain of PLCδ1 fused to GFP. Here we report on a comparative analysis of several recently-described yeast PH domains as well as the mammalian Tubby domain to evaluate their usefulness as PtdIns(4,5)P2 imaging tools. All of the yeast PH domains that have been previously shown to bind PtdIns(4,5)P2 showed plasma membrane localization but only a subset responded to manipulations of plasma membrane PtdIns(4,5)P2. None of these domains showed any advantage over the PLCδ1PH-GFP reporter and were compromised either in their expression levels, nuclear localization or by causing peculiar membrane structures. In contrast, the Tubby domain showed high membrane localization consistent with PtdIns(4,5)P2 binding and displayed no affinity for the soluble headgroup, Ins(1,4,5)P3. Detailed comparison of the Tubby and PLCδ1PH domains showed that the Tubby domain has a higher affinity for membrane PtdIns(4,5)P2 and therefore displays a lower sensitivity to report on changes of this lipid during phospholipase C activation. These results showed that both the PLCδ1PH-GFP and the GFP-Tubby domain are useful reporters of PtdIns(4,5)P2 changes in the plasma membrane, with distinct advantages and disadvantages. While the PLCδ1PH-GFP is a more sensitive reporter, its Ins(1,4,5)P3 binding may compromise its accuracy to measure PtdIns(4,5)P2changes. The Tubby domain is more accurate to report on PtdIns(4,5)P2 but its higher affinity and lower sensitivity may limit its utility when phospholipase C activation is only moderate. These studies also demonstrated that similar changes in PtdIns(4,5)P2 levels in the plasma membrane can differentially regulate multiple effectors if they display different affinities to PtdIns(4,5)P2.
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TL;DR: Depletion of both lipids was required to prevent PM targeting of proteins that interact with acidic lipids or activation of the transient receptor potential vanilloid 1 cation channel, and PI4P contributes to the pool of polyanionic lipids that define plasma membrane identity and to some functions previously attributed specifically to PI(4,5)P2, which may be fulfilled by a more generalpolyanionic lipid requirement.
Abstract: The quantitatively minor phospholipid phosphatidylinositol (4,5)-bisphosphate [PI(4,5)P(2)] fulfills many cellular functions in the plasma membrane (PM), whereas its synthetic precursor, phosphatidylinositol 4-phosphate (PI4P), has no assigned PM roles apart from PI(4,5)P(2) synthesis. We used a combination of pharmacological and chemical genetic approaches to probe the function of PM PI4P, most of which was not required for the synthesis or functions of PI(4,5)P(2). However, depletion of both lipids was required to prevent PM targeting of proteins that interact with acidic lipids or activation of the transient receptor potential vanilloid 1 cation channel. Therefore, PI4P contributes to the pool of polyanionic lipids that define plasma membrane identity and to some functions previously attributed specifically to PI(4,5)P(2), which may be fulfilled by a more general polyanionic lipid requirement.
413 citations
TL;DR: The structural aspects of the deciphering of the 'PI code' by the most common PI-recognizing effectors are highlighted and the mechanistic details of their membrane anchoring are discussed.
Abstract: Phosphoinositide (PI) lipids are essential components of eukaryotic cell membranes. They are produced by mono-, bis- and trisphosphorylation of the inositol headgroup of phosphatidylinositol (PtdIns) and are concentrated in separate pools of cytosolic membranes. PIs serve as markers of the cell compartments and form unique docking sites for protein effectors. Collectively, seven known PIs, the protein effectors that bind them and enzymes that generate or modify PIs compose a remarkably complex protein-lipid signaling network. A number of cytosolic proteins contain one or several effector modules capable of recognizing individual PIs and recruiting the host proteins to distinct intracellular compartment. The recently determined atomic-resolution structures and membrane-targeting mechanisms of a dozen PI effectors have provided insights into the molecular basis for regulation of endocytic membrane trafficking and signaling. In this review, I highlight the structural aspects of the deciphering of the 'PI code' by the most common PI-recognizing effectors and discuss the mechanistic details of their membrane anchoring.
251 citations
TL;DR: This work designed genetically encoded biosensors with distinct relative affinities and expressed them stably in Arabidopsis thaliana and found that PI(4,5)P2 is able to localize PIP2 -interacting protein domains to the plasma membrane in non-stressed root epidermal cells.
Abstract: Phosphatidylinositolphosphates (PIPs) are phospholipids that contain a phosphorylated inositol head group. PIPs represent a minor fraction of total phospholipids, but are involved in many regulatory processes, such as cell signalling and intracellular trafficking. Membrane compartments are enriched or depleted in specific PIPs, providing a unique composition for these compartments and contributing to their identity. The precise subcellular localization and dynamics of most PIP species is not fully understood in plants. Here, we designed genetically encoded biosensors with distinct relative affinities and expressed them stably in Arabidopsis thaliana. Analysis of this multi-affinity 'PIPline' marker set revealed previously unrecognized localization of various PIPs in root epidermis. Notably, we found that PI(4,5)P2 is able to localize PIP2 -interacting protein domains to the plasma membrane in non-stressed root epidermal cells. Our analysis further revealed that there is a gradient of PI4P, with the highest concentration at the plasma membrane, intermediate concentration in post-Golgi/endosomal compartments, and the lowest concentration in the Golgi. Finally, we also found a similar gradient of PI3P from high in late endosomes to low in the tonoplast. Our library extends the range of available PIP biosensors, and will allow rapid progress in our understanding of PIP dynamics in plants.
202 citations
TL;DR: This review discusses current knowledge of the principle types of PPIn-protein interactions, focusing on specific lipid-binding domains, and describes how these domains have been re-tasked by biologists as molecular probes for these lipids in living cells.
196 citations
TL;DR: The kinetic model for signaling from M1 muscarinic receptors is extended and the PIP2 activation of KCNQ channels obeys a cooperative square law and the step synthesizing PIP 2 by PIP 5-kinase is fast and limited primarily by a step(s) that replenishes the pool of plasma membrane PI(4)P.
Abstract: The signaling phosphoinositide phosphatidylinositol 4,5-bisphosphate (PIP2) is synthesized in two steps from phosphatidylinositol by lipid kinases. It then interacts with KCNQ channels and with pleckstrin homology (PH) domains among many other physiological protein targets. We measured and developed a quantitative description of these metabolic and protein interaction steps by perturbing the PIP2 pool with a voltage-sensitive phosphatase (VSP). VSP can remove the 5-phosphate of PIP2 with a time constant of τ <300 ms and fully inhibits KCNQ currents in a similar time. PIP2 was then resynthesized from phosphatidylinositol 4-phosphate (PIP) quickly, τ = 11 s. In contrast, resynthesis of PIP2 after activation of phospholipase C by muscarinic receptors took ∼130 s. These kinetic experiments showed that (1) PIP2 activation of KCNQ channels obeys a cooperative square law, (2) the PIP2 residence time on channels is <10 ms and the exchange time on PH domains is similarly fast, and (3) the step synthesizing PIP2 by PIP 5-kinase is fast and limited primarily by a step(s) that replenishes the pool of plasma membrane PI(4)P. We extend the kinetic model for signaling from M1 muscarinic receptors, presented in our companion paper in this issue (Falkenburger et al. 2010. J. Gen. Physiol. doi:10.1085/jgp.200910344), with this new information on PIP2 synthesis and KCNQ interaction.
182 citations
Cites background from "Live cell imaging with protein doma..."
...This can alter phosphoinositide dynamics, as we and others find (Holz et al., 2000; Raucher et al., 2000; Lei et al., 2001; Várnai et al., 2002; Gamper et al., 2004; Szentpetery et al., 2009)....
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3,341 citations
TL;DR: Inositol phospholipids mediate acute responses, but also act as constitutive signals that help define organelle identity, and play a fundamental part in controlling membrane–cytosol interfaces.
Abstract: Inositol phospholipids have long been known to have an important regulatory role in cell physiology. The repertoire of cellular processes known to be directly or indirectly controlled by this class of lipids has now dramatically expanded. Through interactions mediated by their headgroups, which can be reversibly phosphorylated to generate seven species, phosphoinositides play a fundamental part in controlling membrane-cytosol interfaces. These lipids mediate acute responses, but also act as constitutive signals that help define organelle identity. Their functions, besides classical signal transduction at the cell surface, include regulation of membrane traffic, the cytoskeleton, nuclear events and the permeability and transport functions of membranes.
2,528 citations
"Live cell imaging with protein doma..." refers background in this paper
...PtdIns(4,5)P2 is also important for endocytosis of PM proteins through its binding to several clathrin adaptors [2]....
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TL;DR: In this paper, the PLC(4,5)P2 pools that bind pleckstrin homology (PH) domains were visualized by cellular expression of a PLCδ PH domain and analysis of confocal images in living cells.
Abstract: Phosphatidylinositol 4,5-bisphosphate (PtdIns[4,5]P2) pools that bind pleckstrin homology (PH) domains were visualized by cellular expression of a phospholipase C (PLC)δ PH domain–green fluorescent protein fusion construct and analysis of confocal images in living cells. Plasma membrane localization of the fluorescent probe required the presence of three basic residues within the PLCδ PH domain known to form critical contacts with PtdIns(4,5)P2. Activation of endogenous PLCs by ionophores or by receptor stimulation produced rapid redistribution of the fluorescent signal from the membrane to cytosol, which was reversed after Ca2+ chelation. In both ionomycin- and agonist-stimulated cells, fluorescent probe distribution closely correlated with changes in absolute mass of PtdIns(4,5)P2. Inhibition of PtdIns(4,5)P2 synthesis by quercetin or phenylarsine oxide prevented the relocalization of the fluorescent probe to the membranes after Ca2+ chelation in ionomycin-treated cells or during agonist stimulation. In contrast, the synthesis of the PtdIns(4,5)P2 imaged by the PH domain was not sensitive to concentrations of wortmannin that had been found inhibitory of the synthesis of myo-[3H]inositol– labeled PtdIns(4,5)P2. Identification and dynamic imaging of phosphoinositides that interact with PH domains will further our understanding of the regulation of such proteins by inositol phospholipids.
737 citations
TL;DR: The studies show that PtdIns(4,5)P2 can have second messenger functions of its own, by mediating a transient dissociation of proteins anchored in the plasma membrane.
708 citations
"Live cell imaging with protein doma..." refers background in this paper
...This was finally achieved with the introduction of the PLC1-PH-domain GFP chimera as a molecular probe to detect PtdIns(4,5)P2 in eukaryotic cells [8,9]....
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TL;DR: This study suggests that plasma membrane PIP2 controls dynamic membrane functions and cell shape by locally increasing and decreasing the adhesion between the actin-based cortical cytoskeleton and the plasma membrane.
678 citations
"Live cell imaging with protein doma..." refers background in this paper
...Moreover, PtdIns(4,5)P2 is required for the proper functioning of many ion channels and transporters [3,4] and also contributes to the regulation of actin polymerization [5] and attachment of the PM to the actin cytoskeleton [6]....
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