[FIBA_HUMAN] Defects in FGA are a cause of congenital afibrinogenemia (CAFBN) [MIM:202400]. This is a rare autosomal recessive disorder characterized by bleeding that varies from mild to severe and by complete absence or extremely low levels of plasma and platelet fibrinogen. Note=The majority of cases of afibrinogenemia are due to truncating mutations. Variations in position Arg-35 (the site of cleavage of fibrinopeptide a by thrombin) leads to alpha-dysfibrinogenemias. Defects in FGA are a cause of amyloidosis type 8 (AMYL8) [MIM:105200]; also known as systemic non-neuropathic amyloidosis or Ostertag-type amyloidosis. AMYL8 is a hereditary generalized amyloidosis due to deposition of apolipoprotein A1, fibrinogen and lysozyme amyloids. Viscera are particularly affected. There is no involvement of the nervous system. Clinical features include renal amyloidosis resulting in nephrotic syndrome, arterial hypertension, hepatosplenomegaly, cholestasis, petechial skin rash.
[THRB_BOVIN] Thrombin, which cleaves bonds after Arg and Lys, converts fibrinogen to fibrin and activates factors V, VII, VIII, XIII, and, in complex with thrombomodulin, protein C. Functions in blood homeostasis, inflammation and wound healing (By similarity). [FIBA_HUMAN] Fibrinogen has a double function: yielding monomers that polymerize into fibrin and acting as a cofactor in platelet aggregation.
A peptide containing residues 1-50 of the Aalpha-chain of fibrinogen, expressed as a fusion peptide with beta-galactosidase, is rapidly cleaved by thrombin at Arg-16, similarly to whole fibrinogen. When Phe-8, which is highly conserved, is replaced with tyrosine (F8Y), the cleavage is slowed drastically [Lord, Byrd, Hede, Wei and Colby (1990) J. Biol. Chem. 265, 838-843]. To examine the structural basis for this result, we have determined the crystal structure of bovine thrombin complexed with a synthetic peptide containing residues 1-23 of fibrinogen Aalpha and the F8Y mutation. The crystals are in space group P43212, with unit-cell dimensions of a = 88.3 A (1 A = 0.1 nm), c = 195.5 A and two complexes in the asymmetric unit. The final R factor is 0.183 for 2sigma data from 7.0 to 2.5 A resolution.There is continuous density for the five residues in the P3, P2, P1, P1' and P2' positions of the peptide (Gly-14f to Pro-18f) at the active site of thrombin, and isolated but well-defined density for Tyr-8f at position P9 in the hydrophobic pocket of thrombin. The tyrosine residue is shifted relative to phenylalanine in the native peptide because the phenol side chain is larger and makes a novel, intrapeptide hydrogen bond with Gly-14f. Adjacent peptide residues cannot form the hydrogen bonds that stabilize the secondary structure of the native peptide. Consequently, the 'reaction'geometry at the scissile bond, eight residues from the mutation, is perturbed and the peptide is mostly uncleaved in the crystal structure.
Crystal structure of fibrinogen-Aalpha peptide 1-23 (F8Y) bound to bovine thrombin explains why the mutation of Phe-8 to tyrosine strongly inhibits normal cleavage at Arg-16.,Malkowski MG, Martin PD, Lord ST, Edwards BF Biochem J. 1997 Sep 15;326 ( Pt 3):815-22. PMID:9307032
From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.
↑ Benson MD, Liepnieks J, Uemichi T, Wheeler G, Correa R. Hereditary renal amyloidosis associated with a mutant fibrinogen alpha-chain. Nat Genet. 1993 Mar;3(3):252-5. PMID:8097946 doi:http://dx.doi.org/10.1038/ng0393-252
↑ Malkowski MG, Martin PD, Lord ST, Edwards BF. Crystal structure of fibrinogen-Aalpha peptide 1-23 (F8Y) bound to bovine thrombin explains why the mutation of Phe-8 to tyrosine strongly inhibits normal cleavage at Arg-16. Biochem J. 1997 Sep 15;326 ( Pt 3):815-22. PMID:9307032