Fibrinogen, the principal protein of vertebrate blood clotting is a hexamer
containing two sets of three different chains (α, β, and γ), linked
to each other by disulfide bonds [1,2]. The N-terminal sections of these three
chains contain the cysteines that participate in the cross-linking of the
chains. The C-terminal parts of the α, β and γ chains contain a
domain of about 225 amino-acid residues, which can function as a molecular
recognition unit [2,3,4,5,6]. In fibrinogen as well as in angiopoietin this domain
is implicated in protein-protein interactions. In lectins, such as mammalian
ficolins and invertebrate tachylectin 5A, the fibrinogen C-terminal domain
binds carbohydrates. As shown in the schematic representation this domain
contains four conserved cysteines involved in two disulfide bonds.
| | | |
A B P
'C': conserved cysteine involved in a disulfide bond.
'*': position of the pattern.
'A,B,P': regions within the domain
The 3D structure of the fibrinogen C-terminal domain (see <PDB:1FZA; F>) shows
a fold composed of three separate regions [2,5,6,7]. The N-terminal region, also
termed A domain, forms a helix and a β-sheet held together by the first
disulfide bond. The second region, or B domain, is the largest. The third
region, also termed P domain, forms long extended coil regions and contains
the C-terminal disulfide bond. This P region is the most divergent and
contains most ligand binding sites and in some cases residues implicated in
Some proteins known to contain a fibrinogen C-terminal domain:
- Vertebrate fibrinogen α, β and γ chains.
- Mammalian tenascin-X, an extracellular matrix protein that mediates
interactions between cells and the extracellular matrix and accelerates
collagen fibril formation. The C-terminal fibrinogen domain binds with
fibrillar proteins in the extracellular matrix.
- Vertebrate angiopoietin proteins, which contain a C-terminal fibrinogen
domain that interacts with tyrosine-protein kinase receptor TIE2.
- Mammalian prothrombinase or fibroleukin.
- Sea cucumber fibrinogen-like protein A.
- Fruit fly protein scabrous (gene sca). Scabrous is involved in the
regulation of neurogenesis in Drosophila and may encode a lateral inhibitor
of R8 cells differentiation.
- Horseshoe crab techylectin-5A, a nonself-recognizing lectin with a
fibrinogen C-terminal domain that recognizes carbohydrates.
- Mammalian ficolins, with a collagen-like domain and a C-terminal fibrinogen
domain that contains potential calcium-binding sites and can interact with
As a signature pattern for this domain, we selected the region around the
fourth cysteine. We also developed a profile that covers the entire fibrinogen
In contactin-associated proteins (Cntnap/Caspr) and intelectins (Itln)
only the N-terminal 'A' region of the fibrinogen C-terminal domain is well
conserved and detected.
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