Complement Component 4 Binding Protein Beta
In contrast to its seven alpha-chain partners, complement component 4 binding protein beta (C4BPB) enters the C4BP octamer as a single copy and is encoded by the C4BPB gene. The beta chain is built from three complement control protein (CCP) modules followed by a non-CCP segment, and it does not itself act as a cofactor for C4b inactivation. Its distinguishing feature is the exclusive binding site it provides for protein S, the vitamin K-dependent anticoagulant, thereby linking complement regulation to the coagulation system on endothelial and B-cell surfaces. Hepatocyte-derived and secreted into plasma, C4BPB circulates almost entirely within the assembled complex, and free monomeric forms are essentially not observed.
