| Abstrakt: |
Properdin is a plasma glycoprotein which stabilizes the C3bnBb¯ enzyme complex of the alternative pathway of the complement system1,2. Unlike the classical pathway, which is initiated by interaction of C1q with the Fc regions of IgG or IgM antibodies in immune complexes, the alternative pathway can be directly activated via binding of C3b to surfaces of foreign organisms3,4. The stabilized C3bnBbP¯ complex activates components C3 and C5 resulting in opsonization of foreign material (via C3b) and assembly of the membrane attack complex (via C5b) on target cells. Therefore properdin greatly enhances complement-mediated clearance and inactivation mechanisms in both natural and acquired resistance to infection1,4. This paper shows that the primary amino acid sequence of properdin is composed mainly of six repeating motifs, each of ∼60 amino acids, and that similar sequences are found in thrombospondin5, the circumsporozoite protein of malaria parasites6–8and regions of the membrane-attack components of complement9. These similarities may provide insight into the mechanisms by which parasites avoid host defences mediated by complement. |
