Jump to content

Draculin

From Wikipedia, the free encyclopedia
Draculin
Identifiers
OrganismDesmodus rotundus
SymbolLTF
Entrez112309586
HomoloGene1754
UniProtK9IMD0
Other data
ChromosomeUnplaced: 29.75 - 29.79 Mb
Search for
StructuresSwiss-model
DomainsInterPro

Draculin (named after Count Dracula) is a glycoprotein found in the saliva of vampire bats. It is a single-chain polypeptide protein composed of 708 amino acids, weighing about 88.5 kDa when reduced and 83 kDa when non-reduced, and selectively inhibits FIXa and FXa.[1] It functions as an anticoagulant, inhibiting coagulation factors IX (IXa) and X (Xa) by establishing rapid equilibrium with factor Xa, and is the first natural polypeptide which has been described to show immediate anti-IXa and anti-Xa properties.[2] In addition, Draculin inhibits the conversion of prothrombin to thrombin, preventing fibrinogen from converting to fibrin.[1] These two processes inhibit blood coagulation thus keeping the blood of the bitten victim from clotting while the bat is drinking. The activation of factor X is a common point between the intrinsic and extrinsic pathway of blood coagulation.[1] Activated factor X (FXa) is the sole enzyme that catalyzes the conversion of prothrombine into thrombin, which is vital in the coagulation cascade.[1] Draculin is a member of the Lactoferrin family of proteins that functions as an antibacterial protein in other mammals, but has been co-opted in bat evolution to function as an anticoagulant.[3]

Draculin is a noncompetitive, tight-binding inhibitor of FXa. The inhibition upon contact with the blood of the victim is immediate. Draculin forms equimolar complexes with factor FXa. The formation of draculin-factor Xa is a two-stage process. The first reversible stage is characterized by the following constants: k1 = 1.117*106 M-1*sec-1, k-1 = 15.388*10-1 sec-1. The second irreversible (concentration-independent) stage is characterized by the forward reaction rate constant k2 = 0.072 sec-1. The dissociation constant is determined as the ratio k-1/k1 = 13.76 nM.[4] Because of the immediate inhibition, the reaction is not readily reversible initially, but is a reversible reaction. It does not act on thrombin, trypsin or chymotrypsin and does not express fibrinolytic activity. The protein increases the lag phase as well as the height of the peak of thrombin generation when in plasma, leading to prolonged bleeding.[1] The biological activity of Draculin is highly dependent on glycosylation of the native protein and can be severely affected by the salivation pattern of the animals. [1]

Daily salivation of vampire bats yields a saliva that progressively decreases in anticoagulant activity. However, there is no significant change in overall protein content during this time. After a 4-day period of rest, anticoagulant activity of the saliva is restored. In addition, purified native draculin, obtained from high- and low-activity saliva, shows significant differences in composition of the carbohydrate moiety, and glycosylation pattern. Furthermore, controlled chemical de-glycosylation of native draculin progressively leads to complete loss of the biological activity, despite the conditions leaving the polypeptide backbone intact. These results suggest that oligosaccharides linked to draculin are essential for it to express against Fxa. In addition, it suggests that draculin is actually secreted as a mixture of glycoforms. The final anticoagulant activity of draculin then, in turn, relies on correct glycosylation, implying that glycosylation is the limiting step for production of draculin with optimal anticoagulant properties. In this regard, the appropriate glycosylation of draculin may be in part responsible for the dual, independent, inhibitory action of native draculin on FIXa and FXa, suggesting a novel mechanism of inhibition which is different from other known natural inhibitors of FXa.[1]

Structure

[edit]

Draculin is a single-chain protein composed of 708 amino acids, weighing about 83 kDa with a pI of 4.1-4.2. When reduced, the gel electrophoresis data indicates a slightly higher molecular mass suggesting intra-chain disulphide bonds.[2]

There are two different structural forms of draculin. However, the two forms do not significantly differ from the other. Both structures are able to and do bind to coagulation factors IXa and Xa. The main difference is evident in inhibition activity. One structural form will inhibit factor IXa and the other Xa. The inhibitory activity of one factor is not affected by the presence of the other.[1] FXa-Draculin complex is a two-step mechanism that, through experimental conditions, is reversible.[1]

See also

[edit]

References

[edit]
  1. ^ a b c d e f g h i Fernandez, Ana Z.; Tablante, Alfonso; Beguı́n, Suzette; Hemker, H. Coenraad; Apitz-Castro, Rafael (1999-09-14). "Draculin, the anticoagulant factor in vampire bat saliva, is a tight-binding, noncompetitive inhibitor of activated factor X" (PDF). Biochimica et Biophysica Acta (BBA) - Protein Structure and Molecular Enzymology. 1434 (1): 135–142. doi:10.1016/S0167-4838(99)00160-0. ISSN 0167-4838. PMID 10556567.
  2. ^ a b Apitz-Castro, Rafael; Béguin, Suzette; Tablante, Alfonzo; Bartoli, Fulvia; Holt, John C; Hemker, H Coenraad (1995). "Purification and Partial Characterization of Draculin, the Anticoagulant Factor Present in the Saliva of Vampire Bats (Desmodus rotundus)" (PDF). Thrombosis and Haemostasis. 73 (1): 094–100. doi:10.1055/s-0038-1653731. ISSN 0340-6245. PMID 7740503.
  3. ^ Low DH, Sunagar K, Undheim EA, Ali SA, Alagon AC, Ruder T, Jackson TN, Pineda Gonzalez S, King GF, Jones A, Antunes A, Fry BG (August 2013). "Dracula's children: molecular evolution of vampire bat venom". Journal of Proteomics. 89: 95–111. doi:10.1016/j.jprot.2013.05.034. PMID 23748026.
  4. ^ "Full Article". protein.bio.msu.ru. Archived from the original on 2023-04-22. Retrieved 2023-04-22.
[edit]