Scavenger receptor

Function

It is thought that scavenger receptors participate in the removal of many foreign substances and waste materials in the living body by extensive ligand specificity and a variety of receptor molecules.

In atherosclerotic lesions, macrophages that express scavenger receptors on their plasma membrane aggressively uptake the oxidized LDL deposited in the blood vessel wall inside and become foam cells, and they secrete various inflammatory cytokines and accelerate the development of atherosclerosis.

Types

Scavenger receptors are categorized into classes A, B, and C according to their structural characteristics.

• Class A is mainly expressed in the macrophage, and a protein whose molecular weight is about 80 cysteine-rich domain.
• Class B has two transmembrane regions.
• Class C is a transmembrane protein whose N-terminus is located extracellularly.

Scavenger receptor class A

Scavenger receptors type 1 (SR-A1) and 2 (SR-A2) are trimers with a molecular weight of about 220-250 kDa (the molecular weight of monomeric protein is about 80 kDa). They preferentially bind modified LDL by acetic acid and oxidized LDL. They have a cysteine-rich domains.

Scavenger receptor class B

CD36 and scavenger receptor class B1 (SR-B1) are identified as oxidized LDL receptors and classified into class B. Both proteins have two transmembrane domains, and they are concentrated in a specific plasma membrane microdomain, the caveolae. CD36 has been thought to be implicated in cell adhesion, in the phagocytosis of apoptotic cells, and in the metabolism of long-chain fatty acids. SR-B1 can interact not only with oxidized LDL but also with normal LDL and high density lipoproteins (HDL). Recent studies have indicated that SR-B1 are involved in HDL metabolism.

Others

Some receptors that can bind to oxidized LDL have been discovered.

• CD68 and its mouse homologue, macrosialin, has a unique N-terminal mucin-like domain.
• mucin-like structure.
• Lectin-like oxidized LDL receptor-1 (LOX-1) was isolated from an aortic endothelial cell, and recently it has been discovered in macrophages and vascular smooth muscle cells in artery vessels. The expression of LOX-1 is inducted by inflammatory stimuli, so LOX-1 is thought to be involved in the development of atherosclerotic lesions.