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Structural aspects of rat angiotensinogen.
Summary
Rat angiotensinogen exists in two forms (Ao-1, Ao-2) with similar amino acid and immunological profiles. Differences in carbohydrate structure, particularly oligosaccharide chains, explain variations in molecular weight and charge, impacting antibody binding.
Area of Science:
- Biochemistry
- Proteomics
- Glycobiology
Background:
- Rat angiotensinogen (Ao) presents as two distinct molecular weight forms, Ao-1 and Ao-2.
- Both forms exhibit highly similar amino acid compositions and immunological properties.
Purpose of the Study:
- To investigate the structural basis for the molecular weight and charge heterogeneity of rat angiotensinogen.
- To explore the impact of structural modifications on angiotensinogen's interaction with renin and antibodies.
Main Methods:
- Isoelectric focusing (IEF) and ConA Sepharose CL-6B chromatography to analyze carbohydrate moieties.
- Circular dichroism (CD) spectroscopy to determine secondary structure.
- Radioimmunoassay to assess antibody binding and enzyme assays for renin activity.
Main Results:
- Heterogeneity in isoelectric points and molecular weight between Ao-1 and Ao-2 suggests differences in carbohydrate content, specifically oligosaccharide chains.
- Circular dichroism revealed angiotensinogen's structure (17% alpha-helix, 37% beta-structure, 45% irregular).
- Dithiothreitol (DTT) treatment altered secondary structure and significantly reduced antibody binding, without affecting renin cleavage.
Conclusions:
- The primary differences in rat angiotensinogen's weight and charge are attributed to variations in its glycosylation pattern.
- Structural changes induced by reducing agents like DTT can impair angiotensinogen's antigenicity.
- Angiotensinogen's interaction with renin remains unaffected by DTT-induced structural modifications.