Question

What are the roles of lipid rafts in membrane trafficking and signaling?

Answer 1

Ans -

Lipid rafts - is a microdomains that are enriched with cholestrol, sphingolipids and with specific proteins. The rafts in cells appear to be heterozygous both in terms of their proteins and lipid content, and can be localized to different regions of the cell. Lipid rafts are involved in processes like signal transduction, endocytosis and cholesterol trafficking. Lipid rafts are involved in processes like signal transduction, endocytosis and cholesterol trafficking.

Lipid rafts are normally dispersed in cellular membranes and appear to require specialised machinery to reorganise them to operate. Caveolin-1 and MAL are members of two different protein families involved in reorganisation of lipid rafts for signalling and/or intracellular transport in epithelial cells.

There are two types of lipid rafts – planner (or non- caveolar) and caveolae. Caveolae are flasked shaped invaginations of the plasma membrane that contain caveolin proteins. Caveolin, is a cholesterol binding protein.

Caveolae are distinct flask-shaped plasma membrane invaginations that are highly enriched in cholesterol and the cholesterol-binding, integral membrane protein caveolin, which is essential for caveolae formation. Caveolae have a similar lipid composition as rafts and may form as the result of caveolin-facilitated coalescence of many small rafts. Caveolae are largely immobile structures, which mediate a highly regulated rather than a constitutive form of dynamin-dependent endocytosis. Endocytosis helps materials to move inside or outside the cell.

Lipid rafts helps in cell signalling by attaching some recptors on thier suraface. for example- Various receptors present on immune cells like B cells, T cells, basophils and mast cells associate with lipid rafts on ligand binding and initiate signalling cascades leading to inflammation. it has been seen that , disrupting lipid raft integrity alters lipopolysaccharide‐induced cytokine secretion, IgE signalling, and B‐cell and T‐cell activation.