Apolipoprotein B is a major protein constituent of chylomicrons (apo B-48), LDL (apo B-100) and VLDL (apo B-100). Apo B-100 functions as a recognition signal for the cellular binding and internalization of LDL particles by the apoB/E receptor. Interacts with PCSK9. Interacts with MTTP. Interacts with AUP1. Detected in liver (at protein level). Highly expressed in liver. Detected at lower levels in jejunum, duodenum and kidney.