| In contrast to the apoB/E receptor which has two well-defined ligands (client molecules) scavenger receptors are membrane receptors with broad specificity. They are present on the phagocytic cells such as macrophages (Fig. 17.4). They also differ from the LDL receptor in that they are not subject to feedback regulation, and therefore they may overload the cell with their ligands. There are classes of scavenger receptor designated A and B, and another known as CD36. Class A receptors contain collagen-like triple-helical structure. Class A scavenger receptor does not bind intact LDL but it readily binds chemically modified (acetylated or oxidized) LDL. Class B receptor participates in HDL metabolism.
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| Figure 17.4 LDL and scavenger receptors. While the LDL (apoB/E) receptor mediates the uptake of intact LDL, the scavenger receptor internalizes modified LDL. Both receptors span the cell membranes. The expression of LDL receptor is regulated by the intracellular cholesterol concentration, while the scavenger receptor remains unregulated. The scavenger receptor type A, which is illustrated here, is present on macrophages and has a collagen-like structure. Scavenger receptor type BI participates in HDL-metabolism. |
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