What is the Difference Between Lipid Rafts and Caveolae

The key difference between lipid rafts and caveolae is that a lipid raft is a flat structure while a caveola is an invaginated structure.

Lipid rafts and caveolae are two microdomains of the plasma membrane. They are normally enriched in sphingolipids and cholesterol. Hence, they have less fluid than the remainder of the membrane. Moreover, these two microdomains have two different protein compositions, suggesting that lipids drafts and caveolae have specified roles in the regulation of signalling pathways.

CONTENTS

1. Overview and Key Difference
2. What are Lipid Rafts  
3. What are Caveolae
4. Similarities – Lipid Rafts and Caveolae
5. Lipid Rafts vs Caveolae in Tabular Form
6. Summary – Lipid Rafts vs Caveolae

What are Lipid Rafts?

Lipid raft is a microdomain of the plasma membrane. It has a flat structure. The plasma membranes of the cells contain combinations of glycosphingolipids, cholesterol and protein receptors, which are organized in glycolipoprotein lipid microdomain termed a lipid raft. However, their presence in the plasma membrane is somewhat controversial. It has been proposed that a lipid raft is a specialized membrane microdomain that compartmentalizes cellular processes by serving as an organizing centre for the assembly of signalling molecules. This allows a closer interaction of protein receptors and their effectors to promote kinetically favourable interactions that are important for signal transduction.

The idea of lipid rafts was formally developed by Simons and Ikonen in 1997. At the Keystone Symposium of Lipid Rafts and Cell Function in 1997, lipid rafts were defined as small (70nm) heterogeneous, highly dynamic, sterol and sphingolipid enriched domains that compartmentalize cellular processes. Lipid rafts (planar rafts) are defined as being continuous with the plane of the plasma membrane and are characterized by their lack of distinguishing morphological features. Lipids rafts also contain a specific protein called flotillin.

Lipids rafts are predominately found in the neurons where caveolae are absent. Furthermore, accumulated evidence supports that viruses enter cells via penetration of specific membrane microdomains, including lipid rafts.

What are Caveolae?

Caveola is a microdomain of the plasma membrane having an invaginated structure. Caveolae were discovered by E. Yamada in 1955. Caveolae are flask-shaped invaginations of the plasma membrane that contain specific proteins called caveolin. Caveolin proteins are the most readily observed structure in the caveolae. Caveolae are widely observed in the brain, micro-vessels of the nervous system, endothelial cells, oligodendrocytes, Schwann cells, dorsal root ganglia, and hippocampal neurons.

It has been proposed that caveolins in the caveolae act as tumor suppressors. There are three types of caveolin proteins: caveolin 1, 2, and 3. There are two forms of caveolae known as deep and shallow. These two forms have two different distributions of the three caveolin proteins and respective isoforms.

What are the Similarities Between Lipid Rafts and Caveolae?

• Lipid rafts and caveolae are two microdomains in the plasma membrane.
• Both microdomains are insoluble in detergents.
• They have sphingomyelin, glycosphingolipid, and phosphatidylinositol 4.5- bisphosphate.
• They have specific proteins.
• Furthermore, they are small in size.
• They play specified roles in the regulation of signalling pathways by using their receptors.

What is the Difference Between Lipid Rafts and Caveolae?

Lipid raft is a microdomain of the plasma membrane, having a flat structure, while caveola is a microdomain of the plasma membrane, having a flask-shaped structure. Thus, this is the key difference between lipid rafts and caveolae. Furthermore, the size of the lipid raft is less than 70 nm, while the size of the caveola is around 50-100 nm.

The below infographic presents the differences between lipid rafts and caveolae in tabular form for side by side comparison.

Summary – Lipid Rafts vs Caveolae

There are two main membrane microdomains: lipid rafts and caveolae. Lipid raft is a flat structure, while caveola is an inviginated structure. So, this is the key difference between lipid rafts and caveolae. They are small in size and enriched in sphingolipids and cholesterol. They help to carry out specified roles in the regulation of signalling pathways by using their receptors.

Reference:

1. Laurentiis, Angela, et al. “Lipid Rafts and Caveolae in Signaling by Growth Factor Receptors.” The Open Biochemistry Journal, Bentham Science Publishers Ltd.
2. “Caveolae.” An Overview | ScienceDirect Topics.

Image Courtesy:

1. “Lipid-News-Kraft-5-inch-wide” By 1840567vibin – Own work (CC BY-SA 4.0) via Commons Wikimedia
2. “Caveola TEM” By Krijnse Locker J., Schmid S.L. – Integrated Electron Microscopy: Super-Duper Resolution. PLoS Biol 11(8): e1001639. doi:10.1371/journal.pbio.1001639 (CC BY 4.0) via Commons Wikimedia