Related Experiment Video
Updated: Jul 11, 2026
13:08
Measurement of Factor V Activity in Human Plasma Using a Microplate Coagulation Assay
Published on: September 9, 2012
Profiling the enzymatic properties and inhibition of human complement factor B
Giang Thanh Le1, Giovanni Abbenante, David P Fairlie
1Centre for Drug Design and Development, Institute for Molecular Bioscience, University of Queensland, Brisbane, Queensland 4072, Australia.
The Journal of Biological Chemistry
|October 9, 2007
Summary
Researchers developed a new assay to study human complement factor B, discovering alkaline conditions enhance its activity. This led to the first reversible inhibitor, crucial for understanding complement-mediated immunity and potentially obtaining active enzyme crystal structures.
Area of Science:
- Biochemistry
- Immunology
Background:
- Human complement factor B is a key enzyme in the alternative complement pathway.
- Factor B exists as an inactive zymogen, with crystal structures only available for its inactive form.
Purpose of the Study:
- To profile the catalytic properties of human complement factor B.
- To develop novel assays and inhibitors for studying factor B's function.
Main Methods:
- Utilized para-nitroanilide peptide derivatives as substrates to assay factor B's catalytic activity.
- Investigated the influence of pH and substrate modifications on enzyme kinetics.
- Developed and tested a novel reversible, competitive substrate-based inhibitor.
Main Results:
- Alkaline pH significantly enhanced factor B's substrate cleavage activity.
- N-terminal extensions on substrates increased factor B's catalytic efficiency and cleavage site selectivity.
- A novel inhibitor was developed that blocks C3a and membrane attack complex formation.
Conclusions:
- Optimized conditions and a new inhibitor provide tools for further research into factor B's active conformation.
- This work may facilitate obtaining crystal structures of active factor B and C3 convertase.
- The findings offer new strategies for modulating complement-mediated immunity.
Related Concept Videos
01:27Complement System
The complement system is a group of approximately 20 plasma proteins that strengthen the body's defenses against infections through opsonization, inflammation, and cell lysis. Opsonization involves coating pathogens with complement proteins, making them more recognizable and facilitating phagocyte engulfment. Certain complement proteins induce inflammation that attracts immune cells to the site of infection. Cell lysis involves the destruction of pathogens through the formation of a membrane...
01:30Enzyme Inhibition
Inhibitors are molecules that reduce enzyme activity by binding to the enzyme. In a normally functioning cell, enzymes are regulated by a variety of inhibitors. Drugs and other toxins can also inhibit enzymes. Some inhibitors bind to the enzyme’s active site, while others inhibit enzymatic activity by binding to other sites on the protein structure.