Fibrinogen is a 340 kDa glycoprotein found in the blood plasma of all verte
brates. It is transformed into a fibrin clot by the action of thrombin. Rec
ent X-ray structures of core fragments of both fibrinogen and fibrin have r
evealed many details about this polymerization event. These include structu
res of a 30 kDa recombinant gamma C domain, an 86 kDa fragment D from human
fibrinogen and a cross-linked double-D fragment from fibrin.