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 (PubMed:22580899). Interacts with MTTP (PubMed:26224785, PubMed:27206948). Interacts with AUP1 (PubMed:28183703). Up-regulated in response to enterovirus 71 (EV71) infection (at protein level). Palmitoylated; structural requirement for proper assembly of the hydrophobic core of the lipoprotein particle. The stop codon (UAA) at position 2180 is created by RNA editing. Apo B-48, derived from the fully edited RNA, is produced only in the intestine and is found in chylomicrons. Apo B-48 is a shortened form of apo B-100 which lacks the LDL-receptor region. The unedited version (apo B-100) is produced by the liver and is found in the VLDL and LDL. Genetic variations in APOB define the low density lipoprotein cholesterol level quantitative trait locus 4 (LDLCQ4) [MIM:615558]. The disease is caused by variants affecting the gene represented in this entry. Most cases of FHBL1 result from nonsense mutations in the APOB gene that lead to a premature stop codon, which generate prematurely truncated apo B protein products (PubMed:21981844). The disease is caused by variants affecting the gene represented in this entry. Defects in APOB associated with defects in other genes (polygenic) can contribute to hypocholesterolemia. Apolipoprotein B entry