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