Functions of human complement inhibitor C4b-binding protein in relation to its structure

Area of Science:

• Immunology
• Biochemistry
• Molecular Biology

Background:

• The complement cascade is a critical immune defense but can damage host tissues.
• Complement inhibitors, like C4b-binding protein (C4BP), are essential for self-tissue protection.
• C4BP is a large plasma glycoprotein that inhibits the classical and lectin complement pathways.

Purpose of the Study:

• To review the structure-function relationships of C4BP.
• To elucidate the interactions between C4BP and its ligands, including complement factors C4b and C3b.
• To describe C4BP's diverse functions and its role in pathogenesis.

Main Methods:

• Structural analysis of C4BP and its subunits (alpha and beta chains).
• Investigation of binding interactions with complement factors (C4b, C3b), heparin, and protein S.
• Review of existing literature on C4BP functions and pathogen interactions.

Main Results:

• C4BP's structure, composed of complement control protein (CCP) domains, facilitates its inhibitory functions.
• Detailed mapping of binding sites for C4b, C3b, heparin, and protein S.
• Understanding C4BP's roles in complement inhibition, protection of apoptotic cells, B cell stimulation, and pathogen evasion.

Conclusions:

• C4BP is a multifunctional protein with critical roles in immune regulation and self-protection.
• Structure-function studies provide insights into C4BP's interactions and biological activities.
• C4BP's involvement in pathogenesis highlights its significance in host-pathogen interactions.