Recombinant Human C1QB protein

Supplementary information

This supplementary information is collated from multiple sources and compiled automatically.

C1QB or complement component 1 q subcomponent beta chain is a protein that plays a mechanical role in the complement system. It has a mass of approximately 25 kDa and is expressed in many tissues including the liver and blood plasma. C1QB is a subunit of the C1q complex which is the first component of the classical complement pathway. This protein works with C1q's other subunits to recognize and bind to the Fc region of antibodies facilitating the activation of the complement pathway.

Biological function summary

C1QB is involved in the immune response and helps in the clearance of pathogens and apoptotic cells. It forms part of the C1q complex which includes two other components: C1QA and C1QC. This complex binds to antibodies that are attached to antigens on the surface of pathogens activating the C1r and C1s serine proteases. The activated enzymes then cleave other complement proteins triggering a cascade that results in opsonization inflammation and cell lysis.

Pathways

C1QB takes a significant role in the classical complement pathway and humoral immunity. The classical pathway starts with the binding of the C1 complex to antigen-antibody complexes. Through this mechanism C1QB associates with proteins such as C2 and C4 which further propagate the complement activation cascade. The classical complement pathway links to the lectin pathway where mannose-binding lectin substitutes for C1q to recognize pathogens.

Defects or deficiencies in C1QB relate to systemic lupus erythematosus (SLE) and hereditary angioedema. In SLE impaired function of C1QB leads to decreased clearance of immune complexes contributing to autoimmune reactions. This protein interacts with C1QA in disease mechanisms. In hereditary angioedema although C1QB is not directly defective its involvement in complement activation relates to mutations in C1 inhibitor protein. These mutations result in uncontrolled complement activation underlying the pathophysiology of the disorder.