Function
LDL receptor complexes are present in clathrin-coated pits (or buds) on the cell surface, which when bound to LDL-cholesterol via adaptin, are pinched off to form clathrin-coated vesicles inside the cell. This allows LDL-cholesterol to be bound and internalized in a process known as endocytosis and prevents the LDL just diffusing around the membrane surface. This occurs in all nucleated cells (not erythrocytes), but mainly in the liver which removes ~70% of LDL from the circulation.
Once the coated vesicle is internalized it will shed its clathrin coat and will fuse with an acidic late endosome. The change in pH causes a conformational change in the receptor that releases the bound LDL particle. The receptors are then either destroyed or they can be recycled via the endocytic cycle back to the surface of the cell where the neutral pH will cause the receptor to revert to its native conformation ready to receive another LDL particle.
Synthesis of receptors in the cell is regulated by the level of free intracellular cholesterol; if it is in excess for the needs of the cell then the transcription of the receptor gene will be inhibited. LDL receptors are translated by ribosomes on the endoplasmic reticulum and are modified by the Golgi apparatus before travelling in vesicles to the cell surface.
Read more about this topic: LDL Receptor
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