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