Apart from its physiological role, Factor VIII plays a crucial role in the management of Hemophilia A. As part of treatment, pure or recombinant Factor VIII is given in replacement of the insufficient clotting factor in an effort to successfully manage or avoid bleeding episodes. In conclusion, factor VIII is essential for blood clotting and serves as a key component of specific treatment strategies for the management of hemophilia A.
Including a signal peptide of 19 residues, factor VIII is produced as a single polypeptide chain. The mature factor VIII contains 2332 amino acid residues organized into six domains. Factor VIII appears as a Heavy Chain and Light Chain . With the Heavy Chain [A1-A2-B ] and Light Chain [ A3-C1-C2 ] together, factor VIII crystallizes into a fully functional heterodimer structure. Factor V and Factor VIII are homologous cofactors with identical domain structures. Each functions as a cofactor, meaning it activates other proteins via binding them. A3-C1-C2 sites interact with Factor IXa, the von Willebrand Factor, and the surface of the platelet; whereas the A1 domain site binds Factor X, the A2 domain binds Factor IXa, and the B domain binds both Factor IXa and the von Willebrand Factor.
Below we show the structural similarities of Factor V and Factor VII.
Factor VIII is essentially inactive as a cofactor in blood coagulation, unless it is converted into its active cofactor form by proteolytic cleavage. The binding site for this chemical activation is located in the C2 Domain of the Light Chain, making it an important aspect of our investigation. Furthermore, the C2 Domain has a few interactions with the A1 Domain that stabilize the conformation of the two chains. The - Gln120, Glu122, Lys2239, Gln2266, Leu2302, which are involved in direct contact are . The experimental electron density maps also identify three metal binding sites. Two Cu2+ binding sites and in the A1 domain, with each Cu2+ ion being liganded by two hystidine and one cysteine residue with a trigonal planar coordination geometry. The Ca+ is located in the A3 domain, and liganded by carboxyl groups of aspartate and glutamate residues as well as two backbone carbonyl oxygens.Though the C1 and C2 Domains contain numerous important residues, the most relevant ones in terms of biological functioning of the factor VII are the ones involved in bonding, i.e basic or hydrophobic residues positioned in the hairpin loops at the base of the domains. we highlight the most relevant ones.
The assembly of the factor IXa-factor VIIIa complex is essential in blood-clotting activity. Researchers have identified that mutations in the binding regions of the Factor VIII necessary for the formation of this complex are frequently found in patients with hemophilia A and B. The interaction sites with factor IXa are present throughout the entire protein complex - both in Heavy Chain and Light Chain of Factor VIII. The three distinct interacting regions are: , and , which has been assumed to have the highest affinity for its analogous site of the Factor IX. The respective interaction sites (with the focus on Region III binding residues) necessary for the complex assembly are indicated . Even more interestingly, previous research identified three residues - Arg2215, Lys2249, Leu2251 - in the C2 domain of Factor VIII, whose resemble those of Factor IX's Arg-Leu-Arg helix. This is a remarkable finding considering the fact that - Arg2215, Lys2249, Leu2251 - residues are located on different loops of the C2 domain. It is assumed that this observation of similarities in the structure of the two factors implies additional crystal contact.
Hemophilia A is caused by a variety of mutations in the factor VIII gene and typically requires replacement therapy with purified protein. Because hemophilia is X-linked recessive, it affects men far more commonly than women; 1 in 4,000 to 1 in 5,000 males worldwide. Hemophilia A patients are mostly treated with replacement treatment, which involves injecting concentrates of recombinant or plasma-derived FVIII and FIX intravenously. (Morfini et al., 2013) In the event of bleeding, this is done to replace the coagulation factor deficit or stop the bleeding altogether. For individuals experiencing bleeding episodes, it's important to give factor concentrates as soon as possible. This helps reach the right levels of the missing clotting proteins and continues until the bleeding completely stops. The amount and timing of these infusions vary for people with hemophilia A and B, considering the specific properties of the clotting factor concentrates for Factor VIII and Factor IX. It is evident that replacement therapy for hemophilia has advanced to a high standard in modern times because of the availability of several safe and efficient medicines generated from plasma or recombinant DNA.
For individuals experiencing bleeding episodes, it's important to give factor concentrates as soon as possible. This helps reach the right levels of the missing clotting proteins and continues until the bleeding completely stops. The amount and timing of these infusions vary for people with hemophilia A and B, considering the specific properties of the clotting factor concentrates for Factor VIII and Factor IX. It is evident that replacement therapy for hemophilia has advanced to a high standard in modern times because of the availability of several safe and efficient medicines generated from plasma or recombinant DNA.
Payne, A. B., Miller, C. H., Kelly, F. M., Michael Soucie, J., & Craig Hooper, W. (2013). The CDC Hemophilia A Mutation Project (CHAMP) mutation list: a new online resource.Human mutation, 34(2), E2382–E2391. https://doi.org/10.1002/humu.22247
Stoilova-McPhie S., Lynch G.C., Ludtke S., Pettitt B.M. Domain organization of membrane-bound factor VIII. Biopolymers. 2013 Jul;99(7):448-59. https://doi.org/10.1002/bip.22199.
Morfini, M., Coppola, A., Franchini, M., & Di Minno, G. (2013). Clinical use of factor VIII and factor IX concentrates. Blood transfusion = Trasfusione del sangue, 11 Suppl 4(Suppl 4), s55–s63. https://doi.org/10.2450/2013.010s
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