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Partial sequence of human complement component factor B: novel type of serine protease.
Summary
Factor B is a novel serine protease involved in complement system pathways. Its active site shares homology with other serine proteases, suggesting a unique catalytic mechanism.
Area of Science:
- Biochemistry
- Immunology
- Protease research
Background:
- Factor B is a key component of the alternative complement pathway.
- It is implicated in the enzymatic activity of C3 and C5 convertases.
- Previous studies yielded conflicting results regarding its protease activity.
Purpose of the Study:
- To investigate the proteolytic nature of activated Factor B.
- To determine the location and characteristics of its active site.
- To compare its sequence homology with known serine proteases.
Main Methods:
- Partial amino acid sequencing of the Bb fragment of human Factor B.
- Analysis of NH2-terminal and COOH-terminal sequences.
- Sequence homology comparison with established serine proteases.
Main Results:
- The NH2-terminal sequence of Bb showed no homology with other serine proteases.
- A significant sequence homology was found in the COOH-terminal region.
- Key active site residues (histidine, aspartic acid, serine) were identified in conserved positions.
Conclusions:
- Activated Factor B functions as a novel type of serine protease.
- It possesses a larger catalytic chain compared to previously studied proteases.
- Factor B likely utilizes a distinct activation mechanism within the complement system.