complement component C3b binding

Definition

Target type: molecularfunction

Binding to a C3b product of the complement cascade. [GOC:add, ISBN:0781735149]

Complement component C3b binding is a molecular function that involves the specific interaction between a protein or other molecule and the C3b fragment of complement. C3b is a crucial component of the complement system, a key part of the innate immune system that plays a vital role in defending against pathogens.

C3b is generated through the activation of the complement cascade, a series of enzymatic reactions that ultimately lead to the formation of the membrane attack complex (MAC), which can lyse target cells. C3b binds to the surface of pathogens, such as bacteria, viruses, and fungi, initiating the formation of the MAC.

The binding of C3b to a target surface can occur in two ways:

1. **Direct binding:** C3b can directly bind to certain molecules on the target surface, such as carbohydrates or proteins. This interaction is often facilitated by the presence of specific receptors on the target surface.

2. **Indirect binding:** C3b can bind indirectly to the target surface through other proteins, such as antibodies or complement components. This type of binding often occurs when antibodies are bound to the target surface, creating a pathway for complement activation and C3b deposition.

Once C3b is bound to the target surface, it can trigger several downstream events, including:

* **Opsonization:** C3b serves as an opsonin, a molecule that enhances phagocytosis. Phagocytes, such as macrophages and neutrophils, express receptors for C3b, allowing them to recognize and engulf pathogens coated with C3b.

* **Activation of the alternative pathway:** C3b can activate the alternative pathway of complement, leading to the amplification of the complement cascade and the generation of more C3b.

* **Formation of the MAC:** C3b can participate in the formation of the MAC, which is a complex of complement proteins that can lyse target cells.

Proteins that possess the molecular function of complement component C3b binding often play critical roles in immune responses. They can contribute to pathogen recognition, opsonization, complement activation, and cell lysis. Dysregulation of C3b binding can lead to various immune system disorders, such as autoimmune diseases or impaired immune defense against pathogens.'
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Proteins (1)

Compounds (11)