1rf0
Crystal Structure of Fragment D of gammaE132A Fibrinogen
Structural highlights
DiseaseFIBA_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.[1] FunctionFIBA_HUMAN Fibrinogen has a double function: yielding monomers that polymerize into fibrin and acting as a cofactor in platelet aggregation. Evolutionary Conservation Check, as determined by ConSurfDB. You may read the explanation of the method and the full data available from ConSurf. Publication Abstract from PubMedStructural analysis of recombinant fibrinogen fragment D revealed that the calcium-binding site (beta2-site) composed of residues BbetaAsp261, BbetaAsp398, BbetaGly263, and gammaGlu132 is modulated by the "B:b" interaction. To determine the beta2-site's role in polymerization, we engineered variant fibrinogen gammaE132A in which calcium binding to the beta2-site was disrupted by replacing glutamic acid at gamma132 with alanine. We compared polymerization of gammaE132A to normal fibrinogen as a function of calcium concentration. Polymerization of gammaE132A at concentrations of calcium <or=1 mM exhibited an uncharacteristic 2-3-fold increase in lateral aggregation and fiber thickness compared to normal fibrinogen, while polymerization of variant and normal were indistinguishable at 10 mM calcium. These results suggest that the beta2-site controls the extent of lateral aggregation. That is, when the calcium anchor (beta2-site) is eliminated before "B:b" interactions occur then lateral aggregation is enhanced. We solved structures of fragment D of gammaE132A fibrinogen (rfD-gammaE132A) with and without Gly-His-Arg-Pro-amide (GHRPam) and found no change to the global structure. X-ray diffraction data showed GHRPam binding in the "a" and "b" polymerization sites and that calcium could still bind to the beta2-site of gammaE132A fibrinogen at 70 mM calcium. We found that the gamma2 calcium-binding site (in loop gamma294-301) did not have calcium bound in the structure of fragment D of gammaE132A fibrinogen with GHRPam bound (rfD-gammaE132A+GH). Analysis of structures rfD-gammaE132A+GH and rfD-BbetaD398A+GH indicated that differences in calcium occupation of the gamma2-site resulted from minor conformational changes provoked by crystal packing and GHRPam binding to the "a" site did not directly modulate calcium binding to this site. Calcium-binding site beta 2, adjacent to the "b" polymerization site, modulates lateral aggregation of protofibrils during fibrin polymerization.,Kostelansky MS, Lounes KC, Ping LF, Dickerson SK, Gorkun OV, Lord ST Biochemistry. 2004 Mar 9;43(9):2475-83. PMID:14992585[2] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. See AlsoReferences
| ||||||||||||||||||||
