Fibrin-Anti-Polymerants

Definition
Fibrin-anti-polymerants are small synthetic peptides that can prevent the polymerisation of the thrombin-cleaved fibrinogen by interacting with fibrin monomers1.

Related peptides
These peptides bear a sequence similarity to the terminal sequence of the a- and ß-chains that are exposed following the removal of the fibrinopeptides A and B, respectively, by thrombin1.

Discovery
N-Terminal tetrapeptide analogs of fibrin alpha-chain were first synthesized and studied by Kawasaki et al., in 1992. The inhibitory effects of these peptides on fibrinogen/thrombin clotting were examined. They found that, of the synthetic peptides, amide analogs of Gly-Pro-Arg-Pro exhibited a more potent inhibitory effect2. Later the same group found that, the extension of peptide chain from N-terminal tripeptide decreased the inhibitory effect. The most potent effect was shown by a new N-terminal decapeptide analog, H-Gly-Pro-Arg-Pro-Pro-Glu-Arg-His-Gln-Ser-NH23.

Structural Characteristics
Some commercially available synthetic fibrin anti polymerants bear the following
sequences:
H-Gly-His-Arg-Pro-OH
H-Gly-Pro-Arg-OH
H-Gly-Pro-Arg-Pro-OH
H-Gly-Pro-Arg-Pro-NH2
H-Gly-Pro-Arg-Pro-Pro-Glu-Arg-His-Gln-Ser-NH2

The peptide H-Gly-Pro-Arg-Pro-OH has a sequence similar to the terminal sequence of the a-chain that is exposed following the removal of the fibrinopeptide A by thrombin.The peptide H-Gly-His-Arg-Pro-OH is similar to the terminal sequence of the ß chain after removal of fibrinopeptide B by thrombin. The extension of peptide chain from N-terminal tripeptide decreased the inhibitory effect3.

Mode of Action
The peptide H-Gly-Pro-Arg-Pro-OH can prevent the polymerisation of the thrombin-cleaved fibrinogen by competitively blocking the interaction between the fibrin monomers1.

Functions
Fibrin anti-polymerants are mainly used in various structure-function studies of enzymes and structural proteins like fibrinogen, fibrin etc1.

References
1.Dowd AJ, McGonigle S, Dalton JP (1995). Fasciola hepatica cathepsin L proteinase cleaves fibrinogen and produces a novel type of fibrin clot. Eur. J. Biochem, 232: 241-246.
2.Kawasaki K, Hirase K, Miyano M, Tsuji T, Iwamoto M (1992). Amino acids and peptides. XVI. Synthesis of N-terminal tetrapeptide analogs of fibrin alpha-chain and their inhibitory effects on fibrinogen/thrombin clotting. Chem Pharm Bull (Tokyo). 40(12):3253-3260.
3.Kawasaki K, Tsuji T, Hirase K, Miyano M, Inouye S, Iwamoto M (1993). Amino acids and peptides. XVII. Synthesis of peptides related to N-terminal portion of fibrin alpha-chain and their inhibitory effect on fibrinogen/thrombin clotting. Chem Pharm Bull (Tokyo). 41(3):525-528.