수용체매개 내포작용

Receptor-mediated endocytosis is a specialized form of pinocytosis where cell surface receptors mediate the active uptake of specific molecules such as low-density lipoproteins, otherwise known as LDL, the bad cholesterol.

To initiate the process, adapter proteins interact with specific lipids, phosphatidylinositol phosphates or PIPs in the membrane, to induce a conformational change in the subunits that expose the binding sites for cell surface cargo receptors. When a signal molecule, like LDL, binds to a receptor such as the Apo-B protein here, it causes the membrane to curve inwards, allowing for additional binding in the same vicinity of the growing pit. More protein structures, clathrin triskelions, attach and form the clathrin-coated pit with the cargo facing inside.

Other membrane bending and fusion proteins are recruited to the neck and pinch off the clathrin-coated vesicle. The coating is rapidly released and the naked vesicle will often fuse with endosomes to be further processed by the cell. The cargo receptors disassociate from the LDL in the lower-pH environment within the endosome and intact receptors will be shuttled back to the membrane ready to bind other signaling molecules. The LDL will be further processed and broken down into cholesterol and amino acids.