Structure and biosynthesis of apolipoprotein B

Area of Science:

• Molecular Biology
• Biochemistry
• Cell Biology

Background:

• Apolipoprotein B100 (apo B100) is crucial for lipid transport.
• Understanding apo B100 structure and synthesis is key to lipid metabolism research.

Purpose of the Study:

• To determine the complete sequence of apo B100 cDNA and messenger RNA.
• To analyze the structural features of apo B100 related to lipid binding.
• To investigate the synthesis, intracellular transport, and secretion kinetics of apo B100.

Main Methods:

• DNA/RNA sequencing and computer-based sequence analysis.
• Pulse-chase experiments in Hep G2 cells.
• Analysis of protein localization within the endoplasmic reticulum and Golgi apparatus.

Main Results:

• The complete apo B100 messenger RNA sequence (13,689 nucleotides) was determined, coding for a 4563 amino acid protein (approx. 510,000 MW).
• Structural analysis identified amphipathic alpha-helices and hydrophobic beta-structures, suggesting roles in lipid binding.
• Apo B100 is synthesized as a single unit, secreted within 30 minutes, with specific residence times in the endoplasmic reticulum and Golgi apparatus.

Conclusions:

• The apo B100 sequence and structural motifs provide insights into its function in lipid transport.
• The synthesis and secretion pathway of apo B100 are rapid and efficient, occurring without significant post-translational modification of mass.