Relationship between Amphipathic β Structures in the β₁ Domain of Apolipoprotein B and the Properties of the Secreted Lipoprotein Particles in McA-RH7777 Cells

Abstract

Our previous studies demonstrated that the first 1000 amino acid residues (the βα domain) of human apolipoprotein (apo) B-100, termed apoB:1000, are required for the initiation of lipoprotein assembly and the formation of a monodisperse stable phospholipid (PL)-rich particle. The objectives of this study were (a) to assess the effects on the properties of apoB truncates undergoing sequential inclusion of the amphipathic β strands in the 700 N-terminal residues of the β domain of apoB-100 and (b) to identify the subdomain in the β domain that is required for the formation of a microsomal triglyceride transfer protein (MTP)-dependent triacylglycerol (TAG)-rich apoB-containing particle. Characterization of particles secreted by stable transformants of McA-RH7777 cells demonstrated the following. (1) The presence of amphipathic β strands in the 200 N-terminal residues of the β domain resulted in the secretion of apoB truncates (apoB:1050 to apoB:1200) as both lipidated and lipid-poor particles. (2) Inclusion of residues 300-700 of the β domain led to the secretion of apoB:1300, apoB:1400, apoB:1500, and apoB:1700 predominantly as lipidated particles. (3) Particles containing residues 1050-1500 were all rich in PL. (4) There was a marked increase in the lipid loading capacity and TAG content of apoB:1700-containing particles. (5) Only the level of secretion of apoB:1700 was markedly diminished by MTP inhibitor BMS-197636. These results suggest that apoB:1700 marks the threshold for the formation of a TAG-rich particle and support the concept that MTP participates in apoB assembly and secretion at the stage where particles undergo a transition from PL-rich to TAG-rich.

Apolipoprotein B and Cardiovascular Disease: Biomarker and Potential Therapeutic Target

“…The apoB100 polypeptide is made up of five domains: βα1, β1, α2, β2, and α3, with α representing a predominantly α-helical structure and β representing a predominantly β-sheet structure [ 31 , 32 , 33 ]. The N-terminal sequence is vital in the formation of VLDL due to its interaction with the microsomal triglyceride transfer protein (MTP) [ 34 , 35 ]. MTP in the endoplasmic reticulum is required for the first step in apoB generation, transfer of triglycerides, phospholipids and cholesterol esters to the apoB particle [ 36 ].…”

Novel Biomarkers for Atherosclerotic Disease: Advances in Cardiovascular Risk Assessment

“…The βα1 N-terminal domain is a binding site for microsomal triglyceride transfer protein (MTP). MTP is a specific apoB protein needed for VLDL assembly and for scavenger receptors [ 72 ]. The β1 domain is essential for lipid binding and lipoprotein formation, being the anchor that facilitates the firm adhesion of apoB-100 to the surface of different lipoproteins [ 73 ].…”

Hepatitis C virus induces oxidation and degradation of apolipoprotein B to enhance lipid accumulation and promote viral production

“…However, ApoB could not be overexpressed because of its large molecular weight. C-terminal truncated ApoB can mediate the assembly and secretion of VLDL [46]. We thus sought to determine whether overexpression of ApoB-50 (A) Huh-7 cells were infected with HCV (MOI = 1) for 2 days followed by transduction with gp78 shRNA for 2 days.…”