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Phosphoinositides and PIPs

Phosphoinositides and PIPs

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...

Lipids as Anchors

Lipids as Anchors

In the plasma membrane, the lipids forming the bilayer can also act as an anchor to tether proteins to the membrane. The three main types of lipid anchors found in eukaryotes are – prenyl groups, fatty acyl groups, and glycosylphosphatidylinositol or GPI groups. Prenyl and fatty acyl groups act as anchors on the cytosolic surface of the membrane, whereas GPI anchors proteins on the extracellular side.
The carboxy-terminal of most of the prenylated proteins, such as Ras proteins, contains the...

Membrane Fluidity

Membrane Fluidity

Membrane fluidity is explained by the fluid mosaic model of the cell membrane, which describes the plasma membrane structure as a mosaic of components—including phospholipids, cholesterol, proteins, and carbohydrates—that gives the membrane a fluid character.
Mosaic nature of the membrane
The mosaic characteristic of the membrane helps the plasma membrane remain fluid. The integral proteins and lipids exist as separate but loosely-attached molecules in the membrane. The membrane is a relatively...

Membrane Fluidity

Membrane Fluidity

Cell membranes are composed of phospholipids, proteins, and carbohydrates loosely attached to one another through chemical interactions. Molecules are generally able to move about in the plane of the membrane, giving the membrane its flexible nature called fluidity. Two other features of the membrane contribute to membrane fluidity: the chemical structure of the phospholipids and the presence of cholesterol in the membrane.Fatty acids tails of phospholipids can be either saturated or...

Asymmetric Lipid Bilayer

Asymmetric Lipid Bilayer

Biological membranes show uneven distribution of different types of lipids in the inner and outer layers, resulting in transverse asymmetric membranes. The treatment of the erythrocyte membrane with the enzyme phospholipase confirmed the asymmetric nature of the lipid bilayer. The enzyme hydrolyzes lipids into fatty acids and hydrophilic groups. The phospholipase acts only on the outer layer of the membrane, while the inner layer remains intact. The phospholipase treatment resulted in 80%...

Biosynthesis of Lipids

Biosynthesis of Lipids

Microbial membranes exhibit remarkable diversity in lipid composition, reflecting evolutionary adaptations to various environmental conditions. The three domains of life—Bacteria, Archaea, and Eukarya—synthesize membrane lipids through distinct biosynthetic pathways, leading to fundamental structural differences that impact membrane stability, function, and adaptability.Fatty Acid-Based Lipids in Bacteria and EukaryaBacteria and eukaryotes share a common fatty acid biosynthesis pathway, which...

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Related Experiment Video

Updated: Jun 4, 2026

PIP-on-a-chip: A Label-free Study of Protein-phosphoinositide Interactions

PIP-on-a-chip: A Label-free Study of Protein-phosphoinositide Interactions

Published on: July 27, 2017

Seipin: A central lipid rheostat.

Abdou Rachid Thiam¹, Maxime Carpentier¹

¹Laboratoire de Physique de l'École Normale Supérieure, ENS, Université PSL, CNRS Sorbonne Université, Université Paris-Diderot, Sorbonne Paris Cité, Paris, France.

The Journal of Cell Biology

|June 3, 2026

Summary

Seipin, a flexible protein scaffold, regulates cellular lipid homeostasis and metabolic flux by sensing lipid composition. Its dynamic structure and interactions control lipid pathways, maintaining metabolic stability.

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Area of Science:

Cell Biology
Metabolic Regulation
Lipid Homeostasis

Background:

Seipin is an oligomeric scaffold regulating lipid homeostasis beyond lipid droplet biogenesis.
It senses local lipid composition and membrane features to direct metabolic flux.
Seipin is primarily ER-resident but can relocate to mitochondria-associated membranes.

Purpose of the Study:

To elucidate the regulatory role of seipin in cellular lipid homeostasis.
To understand how seipin's conformational flexibility influences its function.
To propose a unified model for seipin's function as a proteolipid regulatory hub.

Main Methods:

Conformational analysis of seipin.
Investigation of seipin interactions with cofactors and lipid ligands.
Study of seipin localization and function at ER-LD and mitochondria-associated membranes.

Main Results:

Seipin adopts multiple conformations influenced by cofactors and lipids, conferring functional versatility.
Seipin regulates lipid synthesis, turnover, and Ca2+ levels at mitochondria-associated membranes.
Seipin dysfunction leads to lipid imbalance and metabolic/neuronal disorders.

Conclusions:

Seipin acts as a multistate proteolipid regulatory hub, adjusting its structure and interactome dynamically.
It functions as a rheostat controlling lipid pathway decisions in response to metabolic signals.
Seipin is crucial for interorganelle communication and maintaining metabolic stability.