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Pathogenic alpha 1-antitrypsin polymers are formed by reactive loop-beta-sheet A linkage.
P Sivasothy1, T R Dafforn, P G Gettins
1Respiratory Medicine Unit, Department of Medicine, University of Cambridge, The Wellcome Trust Centre for Molecular Mechanisms in Disease, Cambridge Institute for Medical Research, Cambridge, CB2 2XY, United Kingdom.
The Journal of Biological Chemistry
|August 5, 2000
Summary
Polymers of alpha(1)-antitrypsin form through reactive loop insertion into beta-sheet A, a finding crucial for understanding serpinopathies. This research clarifies the structural basis of diseases linked to alpha(1)-antitrypsin deficiency.
Area of Science:
- Biochemistry
- Structural Biology
- Molecular Medicine
Background:
- Alpha(1)-antitrypsin (AAT) is a key circulating protease inhibitor and a member of the serpin superfamily.
- Point mutations can cause AAT to adopt a pathogenic polymeric conformation, linked to diseases like cirrhosis, thrombosis, angioedema, and dementia.
- The exact structural mechanism of AAT polymerization has been debated, with proposed models involving reactive loop insertion into different beta-sheet regions.
Purpose of the Study:
- To elucidate the precise structural linkage within polymers of alpha(1)-antitrypsin.
- To resolve the debate regarding reactive loop insertion into beta-sheet A, C, or strand 7A in AAT polymers.
Main Methods:
- Utilized site-directed cysteine mutants of alpha(1)-antitrypsin.
- Employed fluorescence resonance energy transfer (FRET) to measure distances between monomeric units in AAT polymers.
- Applied a combinatorial approach to compare experimental FRET data with theoretical polymer orientations.
Main Results:
- Experimental FRET measurements provided distance data for polymeric alpha(1)-antitrypsin.
- A combinatorial analysis evaluated 2.9 x 10^6 possible polymer orientations.
- The closest correlation between FRET data and theoretical models confirmed a specific polymer structure.
Conclusions:
- Polymers of alpha(1)-antitrypsin definitively form via insertion of the reactive loop into beta-sheet A.
- This finding provides critical insight into the molecular mechanism underlying serpinopathies associated with AAT.
- The study resolves long-standing questions about AAT polymer structure and its pathogenic implications.