Microsomal triglyceride transfer protein large subunit (MTTP) catalyzes the transport of triglyceride, cholesteryl ester, and phospholipid between phospholipid surfaces, and is required for the secretion of plasma lipoproteins that contain apolipoprotein B. It is a heterodimer consisting of a large MTP alpha-subunit and a protein disulfide isomerase (PDI) beta-subunit. Mutations in microsomal triglyceride transfer protein (MTP) cause abetalipoproteinemia [, , ].
This entry represents a conserved region found in several lipid transport proteins, including vitellogenin, microsomal triglyceride transfer protein and apolipoprotein B-100 [].Vitellinogen precursors provide the major egg yolk proteins that are a source of nutrients during early development of oviparous vertebrates and invertebrates. Vitellinogen precursors are multi-domain apolipoproteins that are cleaved into distinct yolk proteins. Different vitellinogen precursors exist, which are composed of variable combinations of yolk protein components; however, the cleavage sites are conserved. In vertebrates, a complete vitellinogen is composed of an N-terminal signal peptide for export, followed by four regions that can be cleaved into yolk proteins: lipovitellin-1, phosvitin, lipovitellin-2, and a von Willebrand factor type D domain (YGP40) [, ].Microsomal triglyceride transfer protein (MTTP) is an endoplasmic reticulum lipid transfer protein involved in the biosynthesis and lipid loading of apolipoprotein B. MTTP is also involved in the late stage of CD1d trafficking in the lysosomal compartment, CD1d being the MHC I-like lipid antigen presenting molecule [].Apolipoprotein B can exist in two forms: B-100 and B-48. Apoliporotein B-100 is present on several lipoproteins, including very low-density lipoproteins (VLDL), intermediate density lipoproteins (IDL) and low density lipoproteins (LDL), and can assemble VLDL particles in the liver []. Apolipoprotein B-100 has been linked to the development of atherosclerosis.
