Mannan-binding protein, a complement activating animal lectin.

Mannan-binding protein is an animal serum lectin (i.e. a molecule with the ability to bind specifically to certain carbohydrate structures). The relevant carbohydrate ligands are found on many pathogenic microorganisms. After binding to suitable carbohydrate ligands, mannan-binding protein is found to be an activator of the classical pathway of complement via an activation of the C1r2C1s2 complex, i.e. antibody and C1q independent. The molecular organization of MBP resembles that of C1q with a distinct division of collagen-like and globular amino acid sequences. This molecular similarity seems to be the basis for the common functional activity of the two proteins. MBP may play an important protective role, especially at early stages of infection prior to the generation of the specific humoral and cellular defence system. The paper explores the structure and the physiological functions of mannan-binding protein.