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A conserved element in the serine protease domain of complement factor B
D E Hourcade1, L M Mitchell, T J Oglesby
1Department of Medicine, Washington University School of Medicine, St. Louis, Missouri 63110, USA. dhourcad@im.wustl.edu
The Journal of Biological Chemistry
|September 25, 1998
Summary
Investigating a conserved region in Factor B and C2 revealed its critical role in complement convertase assembly and function. Specific mutations severely impaired hemolytic activity, suggesting this region is key for therapeutic complement inhibition.
Area of Science:
- Immunology
- Biochemistry
Background:
- Factor B and C2 are crucial serine proteases in the complement system, forming C3 and C5 convertases.
- These proteases undergo conformational changes upon convertase assembly and dissociation, regulating their activity.
Purpose of the Study:
- To investigate the functional significance of an 8-amino acid conserved sequence shared by Factor B and C2.
- To determine the role of this conserved region in the catalytic activity and regulation of complement convertases.
Main Methods:
- Generation of 24 single amino acid substitution mutants of Factor B within the conserved region.
- Assessment of hemolytic activity of Factor B mutants.
- Analysis of complement convertase assembly steps and C3 cleavage activity.
Main Results:
- Most Factor B mutants showed neutral function, but substitutions at Asp715 and Phe716 significantly reduced hemolytic activity.
- Some Asp715 mutants allowed convertase assembly and Factor D-mediated cleavage but failed to cleave C3.
- This indicates a critical role for the conserved region in catalytic site regulation.
Conclusions:
- The conserved region in Factor B and C2 is vital for conformational regulation of the catalytic site.
- This region represents a potential highly specific target for therapeutic inhibition of the complement system.