What is the only structural protein found in LDL?

Low-density lipoprotein (LDL) is a key component in the transport of cholesterol in the bloodstream and is classified as a lipoprotein. It plays a significant role in the development of atherosclerosis when present in excess. The only structural protein found in LDL is ApoB-100.

ApoB-100 is essential for the structural integrity of LDL particles and serves as a ligand for the LDL receptor, facilitating the uptake of LDL by various cells, particularly in the liver. This protein ensures that the lipoprotein complex remains stable and functional in its role of cholesterol transport.

In contrast, while ApoA-1, ApoC-II, and ApoE are important apolipoproteins, they are not structural components of LDL. ApoA-1 is primarily associated with high-density lipoprotein (HDL), ApoC-II plays a role in the metabolism of triglyceride-rich lipoproteins, and ApoE is involved in chylomicron and VLDL (very-low-density lipoprotein) metabolism, thus not being specific to LDL. Hence, the specific structural role of ApoB-100 in LDL is what makes it the correct answer.