Structure, evolution, and tissue-specific synthesis of human apolipoprotein AIV

Area of Science:

• Molecular Biology
• Genetics
• Biochemistry

Background:

• Apolipoprotein AIV (apoAIV) is a key protein in the lipid transport system.
• It is associated with lipoproteins like chylomicrons and HDL.
• The human apoAIV gene is genetically linked to apoAI and apoCIII genes.

Purpose of the Study:

• To isolate and characterize a nearly full-length human apoAIV cDNA clone.
• To determine the amino acid sequence and structural features of human apoAIV.
• To compare human apoAIV with its rat counterpart to understand evolutionary dynamics.

Main Methods:

• Screening of an adult human liver DNA library using a human apoAIV gene probe.
• In-frame translation of the isolated cDNA sequence to predict amino acid composition.
• Alignment and comparison of human and rat apoAIV amino acid sequences.
• Hybridization blotting analysis of total RNA from various tissues to determine mRNA levels.

Main Results:

• A nearly full-length human apoAIV cDNA clone was successfully isolated.
• Human apoAIV comprises 396 amino acid residues, including a 20-residue signal peptide.
• The protein contains nucleotide and amino acid repeats with potential amphipathic helix structures.
• Human and rat apoAIV share 61.8% amino acid homology, with a five-residue deletion in the rat protein.
• Evolutionary rates of certain amino acid repeats exceed that of the entire apoAIV protein.
• Despite evolutionary differences, secondary structures and hydropathy profiles of repeats are conserved.

Conclusions:

• The study provides a detailed characterization of the human apoAIV cDNA and protein.
• Comparative analysis reveals significant homology and conserved structural features between human and rat apoAIV.
• The findings offer insights into the evolutionary mechanisms and functional significance of apoAIV.