membrane raft/lipid raft parentage -> plasma membrane raft

[ValWood]

Discussion at the GO meeting about whether

membrane raft could have the parentage "plasma membrane"

#5894
Quoting from PMID:16645198, which is the reference for the GO term ‘GO:0045121 !membrane raft’ (the reference title “Rafts defined: a report on the Keystone symposium on lipid rafts and cell function”):

Although “plasma membrane” was suggested for inclusion in the definition of membrane rafts, it was quickly excluded from consideration. Presentations and posters indicating the existence of raft-like domains on intracellular membranes such as the endoplasmic reticulum and mitochondria made it clear that the plasma membrane does not hold a monopoly on membrane domains. Although the nature of such “non-plasma membrane” membrane domains is not yet known, room must be left in the tent to welcome these newcomers.

Thus the current parentage for “membrane raft” is correct, as rafts do not solely occur in the plasma membrane.

based on this. However, one option is to review our annotations and change the label to
"plasma membrane raft"

this would improve annotation propagation and consistency, because despite this discussion, the consensus in the literature seems to be that membrane rafts are plasma membrane features.

CHATGPT
Lipid rafts are specialized, dynamic microdomains within the plasma membrane of cells. They are enriched in cholesterol, sphingolipids, and certain proteins, and are more ordered (less fluid) than the surrounding membrane.
Key Features:
• Composition: High in cholesterol, glycosphingolipids, and saturated phospholipids.
• Structure: More tightly packed and ordered due to saturated lipid chains and cholesterol.
• Size: Typically 10–200 nanometers in diameter.
• Function:
◦ Organize signaling molecules (e.g. receptors, kinases).
◦ Regulate membrane protein trafficking.
◦ Facilitate pathogen entry or immune responses.
◦ Involved in endocytosis and exocytosis.
Controversy and Current Understanding:
Lipid rafts were once controversial due to difficulties in visualizing them directly. However, advanced imaging and biochemical techniques now support their existence and dynamic behavior.

I will try to locate examples of non-PM membrane rafts, but I haven't encountered any in the 16 years since I originally requested this parent be added.

cc @huaiyumi

[ValWood]

🧪 Lipid Composition and Raft Potential by Organelle

Organelle	Cholesterol Content	Sphingolipid Content	Raft-Forming Capacity	Notes
Plasma Membrane	High (~30–40%)	High	Very High	Classic site for rafts; critical for signaling, endocytosis, pathogen entry
Golgi Apparatus	Moderate (~10–20%)	Moderate	Moderate	Raft-like domains may help sort proteins/lipids for transport
Endosomes/Lysosomes	Low to moderate	Low to moderate	Variable	Late endosomes may have raft-like regions important in sorting/degradation
Endoplasmic Reticulum	Low (~1–5%)	Very low	Very Low	Minimal raft formation; lipid synthesis and distribution hub
Mitochondrial Membranes	Very low (~1%)	Very low	Unclear/Low	Generally do not form classical rafts; cardiolipin is the key unique lipid
Nuclear Envelope	Low	Low	Poorly Characterized	Continuity with ER; raft potential is limited

Key Differences in Raft Composition

Feature	Plasma Membrane Rafts	Non-PM Rafts (e.g., Golgi, Endosomes, MAMs)
Cholesterol	Very high (~30–40% of total lipids)	Lower (~5–20%), varies by organelle
Sphingolipids	High (e.g., sphingomyelin, gangliosides)	Moderate to low; often different sphingolipid species
Phospholipid Saturation	Enriched in saturated phosphatidylcholine (PC)	May contain more unsaturated PCs, depending on organelle
Glycosphingolipids	Abundant (e.g., GM1, GM3, Gb3)	Present but often in different ratios or species
Proteins	GPI-anchored proteins, Src-family kinases, flotillins	Cargo sorting proteins, SNAREs, ERLINs, AMBRA1, organelle-specific
Detergent Resistance	High (classic "detergent-resistant membranes")	Variable; often less resistant or biochemically distinct
Functional Roles	Signal transduction, pathogen entry, cytoskeletal anchoring	Vesicle sorting, autophagy, apoptosis, ER-mitochondria signaling

[ValWood]

papers describing non PM rafts call them raft-like domains

e.g. https://www.nature.com/articles/cdd2009208?utm_source=chatgpt.com
mitochondrial raft-like domains