Decay-accelerating factor

DAF regulates the complement system on the cell surface. It recognizes C4b and C3b fragments that are created during activation of C4 (classical or lectin pathway) or C3 (alternative pathway). Interaction of DAF with cell-associated C4b of the classical and lectin pathways interferes with the conversion of C2 to C2b, thereby preventing formation of the C4b2a C3-convertase, and interaction of DAF with C3b of the alternative pathway interferes with the conversion of factor B to Bb by factor D, thereby preventing formation of the C3bBb C3 convertase of the alternative pathway. Thus, by limiting the amplification convertases of the complement cascade, DAF indirectly blocks the formation of the membrane attack complex.

This glycoprotein is broadly distributed among hematopoietic and non-hematopoietic cells. It is a determinant for the Cromer blood group system.

Structure

DAF is a 70 kDa membrane protein that attaches to the cell membrane via a glycophosphatidylinositol (GPI) anchor.

DAF contains four complement control protein (CCP) repeats with a single N-linked glycan positioned between CCP1 and CCP2. CCP2, CCP3, CCP4 and three consecutive lysine residues in a positively charged pocket between CCP2 and CCP3 are involved in its inhibition of the alternate complement pathway. CCP2 and CCP3 alone are involved in its inhibition of the classical pathway.