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Three-dimensional structure and molecular modelling of C1- inhibitor
1Department of Biochemistry and Chemistry, Royal Free Hospital School of Medicine, London, U.K.
Behring Institute Mitteilungen
|December 1, 1993
Summary
New research reveals the two-domain structure of C1 inhibitor, a key protein in the complement system. This protein undergoes significant structural changes during inactivation, affecting its entire secondary structure, not just the reactive site.
Area of Science:
- Biochemistry
- Structural Biology
- Immunology
Background:
- C1 inhibitor (C1-INH) is a crucial regulator of the complement system.
- Previous structural data for C1-INH was limited, hindering a full understanding of its function and regulation.
Purpose of the Study:
- To elucidate the detailed molecular structure of C1 inhibitor.
- To investigate the structural basis of C1 inhibitor inactivation.
Main Methods:
- Amino acid and nucleic acid sequencing
- Carbohydrate content analysis
- Neutron scattering
- X-ray crystallography
- Nuclear Magnetic Resonance (NMR) spectroscopy
- Fourier Transform Infrared (FTIR) spectroscopy
- Microcalorimetry
Main Results:
- C1 inhibitor is a two-domain protein with a distinct structural organization.
- The calculated molecular weight is 71,100 Da, differing from SDS-PAGE estimates.
- Neutron scattering and microcalorimetry confirm the two-domain structure, with an extended N-terminal domain and a C-terminal SERPIN domain.
- Structural analysis reveals significant changes in secondary structure (alpha-helix and beta-sheet content) throughout the molecule upon cleavage and inactivation, not limited to the reactive center loop.
Conclusions:
- The study provides a comprehensive structural model of C1 inhibitor.
- Inactivation of C1 inhibitor involves widespread conformational changes affecting the entire protein structure.
- These findings enhance our understanding of C1 inhibitor function and regulation within the complement cascade.
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