APOB (Apolipoprotein B): APOB is a key protein component of low-density lipoproteins (LDL), which transport cholesterol through the bloodstream. It exists mainly in two forms — APOB-48 and APOB-100, with APOB-100 essential for LDL structure and binding to LDL receptors, enabling cholesterol uptake by cells. High levels of APOB-containing lipoproteins are linked to increased risk of atherosclerosis and cardiovascular disease due to plaque buildup in arteries.