FICOLINS AND THE FIBRINOGEN-LIKE DOMAIN

Ficolins are a group of proteins containing collagen-hire and fibrinog en-like (FBG) sequences and they have a similar overall structure to C lq and the collectins. There are two types of ficolin in man: L-ficoli n and M-ficolin. L-ficolin is synthesized in the liver and secreted in to the plasma. It binds to several apparently unrelated structures inc luding sugar residues and enhances phagocytosis of bound bacteria. M-f icolin is synthesized mainly in monocytes and is detected on the monoc yte surface. The polypeptide sequences of ficolins, the collectins and Clq diverge mainly in their C-terminal globular regions which are, re spectively, FBG domains, Ca2+-dependent: carbohydrate recognition doma ins (C-type CRD), and collagen-related sequences. The FBG domain consi sts of 220-250 residues and is found in a number of proteins besides f ibrinogen and ficolins. The crystal structure of the FBG domain has be en characterized and the elucidation of its binding properties should provide essential insights into its role in ficolins and other protein s.