Tangier disease. The complete mRNA sequence encoding for preproapo-A-I.

Area of Science:

• Molecular Biology
• Genetics
• Biochemistry

Background:

• Tangier disease is characterized by severe deficiency of high-density lipoprotein (HDL) and accumulation of cholesteryl esters.
• Apolipoprotein A-I (apo-A-I) is the major protein component of HDL and plays a crucial role in reverse cholesterol transport.
• The rapid catabolism of apo-A-I is a hallmark of Tangier disease, but its underlying cause remains unclear.

Purpose of the Study:

• To elucidate the molecular basis of apo-A-I abnormalities in Tangier disease.
• To determine the complete amino acid sequence of preproapo-A-I in Tangier disease patients.
• To investigate whether structural defects in apo-A-I contribute to its rapid catabolism.

Main Methods:

• Construction of a Tangier liver cDNA library.
• Nucleic acid sequence analysis of cloned apo-A-I cDNA.
• Specific primer extension analysis on Tangier liver mRNA.
• Comparison of Tangier preproapo-A-I sequence with normal preproapo-A-I.

Main Results:

• Two apo-A-I-containing cDNA clones were identified from the Tangier liver library.
• The complete derived amino acid sequence of Tangier preproapo-A-I was established.
• Tangier preproapo-A-I differed from normal preproapo-A-I by a single base substitution (G to T) at position 120, resulting in an isosteric replacement of glutamic acid with aspartic acid.
• No major structural defect was found in Tangier apo-A-I.

Conclusions:

• The structural defect in apo-A-I in Tangier disease is minimal and unlikely to be the primary cause of its rapid catabolism.
• The accelerated breakdown of apo-A-I in Tangier disease is likely due to a post-translational defect in its metabolism.
• These findings provide insights into the pathogenesis of Tangier disease and apo-A-I metabolism.