Translation and processing of normal (PiMM) and abnormal (PiZZ) human alpha 1-antitrypsin
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Abstract:
Human liver mRNA isolated from subjects phenotyped as homozygous PiMM or PiZZ alpha 1-antitrypsin, was translated in a reticulocyte cell-free system, and alpha 1-antitrypsin identified by immunoprecipitation. In the presence of dog pancreas membranes the translated alpha 1-antitrypsin appeared as a larger product. Treatment with endo-beta-N-glucosaminidase yielded a protein smaller than the reticulocyte translated product, presumably due to removal of the N-terminal signal sequence by membranes and sugar residues by endo-beta-N-glucosaminidase. Quantitation of alpha 1-antitrypsin translated from PiMM and PiZZ livers suggests that both mRNA species were present at the same cellular concentration, and that processing to the core glycosylation stage proceeded at identical rates.
Insights
Alpha 1-antitrypsin (A1AT) mRNA from PiMM and PiZZ human livers was translated. Both genotypes showed similar A1AT mRNA levels and processing rates to the core glycosylation stage.
Area of Science:
- Biochemistry
- Molecular Biology
- Genetics
Background:
- Alpha 1-antitrypsin deficiency (A1AD) is a genetic disorder that can lead to lung and liver disease.
- The PiZZ genotype is associated with severe A1AD, while PiMM is the normal genotype.
- Understanding A1AT synthesis and processing is crucial for A1AD research.
Purpose of the Study:
- To compare the expression and processing of alpha 1-antitrypsin (A1AT) mRNA between PiMM and PiZZ human liver genotypes.
- To investigate the post-translational modifications of A1AT in a cell-free system.
Main Methods:
- Human liver mRNA from PiMM and PiZZ subjects was translated using a reticulocyte cell-free system.
- Immunoprecipitation was used to identify translated A1AT.
- Dog pancreas membranes were used to assess signal peptide processing.
- Endo-beta-N-glucosaminidase treatment was employed to analyze glycosylation.
Main Results:
- Translated A1AT from PiMM and PiZZ livers showed similar mRNA concentrations.
- A larger A1AT product was observed in the presence of dog pancreas membranes, indicating signal sequence removal.
- Treatment with endo-beta-N-glucosaminidase resulted in a smaller product, confirming removal of sugar residues.
- Processing to the core glycosylation stage occurred at identical rates for both genotypes.
Conclusions:
- The study suggests that A1AT mRNA levels and early post-translational processing are similar in PiMM and PiZZ human livers.
- These findings imply that differences in A1AT deficiency severity are not due to differential mRNA expression or initial glycosylation rates.