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Related Concept Videos

Phosphoinositides and PIPs01:42

Phosphoinositides and PIPs

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Phosphoinositides are a group of phospholipids containing a glycerol backbone with two fatty acid chains and a phosphate attached to a myoinositol sugar ring. The inositol head group extends into the cytoplasm, where it is modified by adding phosphate groups to form phosphatidylinositol phosphates or PIPs.
Different phosphoinositides are synthesized and recruited on the cytosolic face of the plasma membrane. The localization of specific phosphoinositides concentrated in separate membrane...
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IP3/DAG Signaling Pathway01:11

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Membrane lipids such as phosphatidylinositol (PI) are precursors for several membrane-bound and soluble second messengers. Specific kinases phosphorylate PI and produce phosphorylated inositol phospholipids. One such inositol phospholipids are the  phosphatidylinositol-4,5 bisphosphate [PI(4,5)P2], present in the inner half of the lipid bilayer. Upon ligand binding, GPCR stimulates Gq proteins to turn on phospholipase Cꞵ. Activated phospholipase Cꞵ cleaves PI(4,5)P2 and...
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Amplifying Signals via Enzymatic Cascade01:22

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When a ligand binds to a cell-surface receptor, the receptor's intracellular domain changes shape, which may either activate its enzyme function or allow its binding to other molecules. The initial signal is amplified by most signal transduction pathways. This means that a single ligand molecule can activate multiple molecules of a downstream target. Proteins that relay a signal are most commonly phosphorylated at one or more sites, activating or inactivating the protein. Kinases catalyze...
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What are Second Messengers?01:12

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Because many receptor binding ligands are hydrophilic, they do not cross the cell membrane and thus their message must be relayed to a second messenger on the inside. There are several second messenger pathways, each with their own way of relaying information. G-protein coupled receptors can activate both phosphoinositol and cyclic AMP (cAMP) second messenger pathways. The phosphoinositol path is active when the receptor induces phospholipase C to hydrolyze the phospholipid,...
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Amplifying Signals via Second Messengers01:15

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Many receptor binding ligands are hydrophilic; they do not cross the cell membrane but bind to cell-surface receptors. Thus, their message must be relayed by second messengers present in the cell cytoplasm. There are several second messenger pathways, each with its own way of relaying information. For example, the G protein-coupled receptors can activate both phosphoinositol and cyclic AMP (cAMP) second messenger pathways. The phosphoinositol pathway is active when the receptor induces...
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GPI Anchoring of Proteins in the ER Membrane01:29

GPI Anchoring of Proteins in the ER Membrane

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GPI-anchoring is a post-translational, reversible protein modification that is ubiquitous in eukaryotes. Such proteins are primarily present on the exoplasmic leaflet of the plasma membrane.
GPI-anchor structure
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Related Experiment Video

Updated: Mar 27, 2026

Identification of Inositol Phosphate or Phosphoinositide Interacting Proteins by Affinity Chromatography Coupled to Western Blot or Mass Spectrometry
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Identification of Inositol Phosphate or Phosphoinositide Interacting Proteins by Affinity Chromatography Coupled to Western Blot or Mass Spectrometry

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A phosphoinositide conversion mechanism for exit from endosomes.

Katharina Ketel1, Michael Krauss1, Anne-Sophie Nicot2

  • 1Leibniz-Institut für Molekulare Pharmakologie, 13125 Berlin, Germany.

Nature
|January 14, 2016
PubMed
Summary

Cellular membrane identity relies on phosphoinositides. This study reveals MTM1 converts phosphatidylinositol 3-phosphate (PI(3)P) to phosphatidylinositol 4-phosphate (PI(4)P) for exocytosis, linking defects to myotubular myopathy.

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Single-molecule Super-resolution Imaging of Phosphatidylinositol 4,5-bisphosphate in the Plasma Membrane with Novel Fluorescent Probes
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Fluorescence-Based Measurements of Phosphatidylserine/Phosphatidylinositol 4-Phosphate Exchange Between Membranes
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Identification of Inositol Phosphate or Phosphoinositide Interacting Proteins by Affinity Chromatography Coupled to Western Blot or Mass Spectrometry
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Single-molecule Super-resolution Imaging of Phosphatidylinositol 4,5-bisphosphate in the Plasma Membrane with Novel Fluorescent Probes
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Fluorescence-Based Measurements of Phosphatidylserine/Phosphatidylinositol 4-Phosphate Exchange Between Membranes
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Area of Science:

  • Cell Biology
  • Molecular Biology
  • Biochemistry

Background:

  • Phosphoinositides regulate vital cell functions including signaling and membrane trafficking.
  • Specific phosphoinositides mark cellular compartments; phosphatidylinositol 3-phosphate (PI(3)P) is found on endosomes, while phosphatidylinositol 4-phosphate (PI(4)P) is at the plasma membrane.
  • Regulated conversion of phosphoinositides is essential for directional membrane traffic between endosomal and secretory pathways.

Purpose of the Study:

  • To elucidate the molecular mechanism of phosphoinositide conversion during endosomal cargo exit via exocytosis.
  • To investigate the role of the phosphatidylinositol 3-phosphatase MTM1 in this process.
  • To explore the link between defective phosphoinositide conversion and X-linked centronuclear myopathy.

Main Methods:

  • Investigated the role of MTM1 in cargo delivery from endosomes to the cell surface.
  • Analyzed phosphoinositide dynamics using biochemical assays.
  • Examined the recruitment of the exocyst complex to endosomes.

Main Results:

  • Surface delivery of endosomal cargo requires PI(3)P hydrolysis by MTM1.
  • MTM1-dependent removal of PI(3)P is coupled with PI4K2α-mediated generation of PI(4)P.
  • This phosphoinositide switch facilitates exocyst complex recruitment and membrane fusion for exocytosis.

Conclusions:

  • Established a mechanism for phosphoinositide conversion from PI(3)P to PI(4)P at endosomes during exocytosis.
  • Defective MTM1 function impairs this conversion, leading to impaired exocytosis.
  • This phosphoinositide conversion defect is proposed as the underlying cause of X-linked centronuclear myopathy.