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In vitro synthesis of M and Z forms of human alpha 1-antitrypsin
Abstract:
mRNA was prepared from autopsy liver samples from a homozygote for alpha 1-antitrypsin deficiency (PiZZ) and from a normal (PiMM) subject. Both preparations gave equivalent synthesis of alpha 1-antitrypsin in a wheat germ cell-free system. This suggests that the deficiency of plasma alpha 1-antitrypsin associated with the Z variant is due to a failure of processing and secretion of the protein rather than of its synthesis. It is likely that it is the resultant intracellular accumulation of the Z protein rather than a deficiency of protease inhibitor that is the primary cause of the liver pathology associated with this variant.
Insights
Alpha 1-antitrypsin deficiency (PiZZ) is caused by faulty protein processing, not synthesis issues. Intracellular Z protein buildup, not low protease inhibitor levels, likely drives liver damage in PiZZ individuals.
Area of Science:
- Biochemistry
- Genetics
- Molecular Biology
Background:
- Alpha 1-antitrypsin deficiency is a genetic disorder.
- The Z variant (PiZZ) is associated with reduced plasma levels of alpha 1-antitrypsin.
- Liver pathology is observed in individuals with the Z variant.
Purpose of the Study:
- To investigate the synthesis of alpha 1-antitrypsin in PiZZ versus PiMM subjects.
- To determine if the deficiency is due to impaired protein synthesis or post-synthesis processing.
- To elucidate the primary cause of liver pathology in alpha 1-antitrypsin deficiency.
Main Methods:
- mRNA extraction from autopsy liver samples of PiZZ and PiMM individuals.
- In vitro synthesis of alpha 1-antitrypsin using a wheat germ cell-free system.
Main Results:
- Equivalent synthesis of alpha 1-antitrypsin was observed from both PiZZ and PiMM mRNA preparations.
- This indicates that the protein is synthesized effectively in PiZZ individuals.
Conclusions:
- The plasma deficiency of alpha 1-antitrypsin in PiZZ is likely due to impaired protein processing and secretion, not synthesis.
- Intracellular accumulation of the Z protein, rather than low protease inhibitor levels, is the probable cause of liver pathology.