Isolation and characterization of rat complement factor B and its interaction with cell-bound human C3.

Area of Science:

• Biochemistry
• Immunology
• Proteomics

Background:

• The complement system is crucial for innate immunity.
• Factor B is a key component of the alternative pathway of complement activation.
• Understanding Factor B's properties is essential for studying complement function.

Purpose of the Study:

• To isolate and characterize native rat Factor B (Brat).
• To confirm Brat's functional integrity and molecular properties.
• To establish a baseline for complement research in rats.

Main Methods:

• Sequential chromatography (QAE-A50, Biorex-70, Sephadex G-200).
• Immunoelectrophoresis and immunodiffusion for protein identification.
• Sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) for purity and molecular weight analysis.
• Functional assays involving cobra venom factor (CoVF) and C3 cleavage.

Main Results:

• Rat Factor B (Brat) was purified with 8-15% recovery, yielding a homogeneous protein.
• Native Brat exhibited beta electrophoretic mobility and a molecular weight of 100,000, remaining unchanged after reduction.
• Brat demonstrated functional activity by forming a C3 convertase with CoVF and human complement component C1, cleaving both rat and human C3.
• Zymosan treatment cleaved Brat into alpha and gamma fragments, indicating its role in complement activation.

Conclusions:

• Rat Factor B (Brat) was successfully isolated in its native, functional form.
• The characterization confirms Brat's molecular weight and its essential role in the complement alternative pathway.
• The study provides a foundation for further investigations into rat complement biology.