title: Amelioration of the severity of heparin-binding antithrombin mutations by posttranslational mosaicism.
abstract: The balance between actions of procoagulant and anticoagulant factors protects organisms from bleeding and thrombosis. Thus, antithrombin deficiency increases the risk of thrombosis, and complete quantitative deficiency results in intrauterine lethality. However, patients homozygous for L99F or R47C antithrombin mutations are viable. These mutations do not modify the folding or secretion of the protein, but abolish the glycosaminoglycan-induced activation of antithrombin by affecting the heparin-binding domain. We speculated that the natural β-glycoform of antithrombin might compensate for the effect of heparin-binding mutations. We purified α- and β-antithrombin glycoforms from plasma of 2 homozygous L99F patients. Heparin affinity chromatography and intrinsic fluorescence kinetic analyses demonstrated that the reduced heparin affinity of the α-L99F glycoform (K(D), 107.9 ± 3nM) was restored in the β-L99F glycoform (K(D), 53.9 ± 5nM) to values close to the activity of α-wild type (K(D), 43.9 ± 0.4nM). Accordingly, the β-L99F glycoform was fully activated by heparin. Similar results were observed for recombinant R47C and P41L, other heparin-binding antithrombin mutants. In conclusion, we identified a new type of mosaicism associated with mutations causing heparin-binding defects in antithrombin. The presence of a fully functional β-glycoform together with the activity retained by these variants helps to explain the viability of homozygous and the milder thrombotic risk of heterozygous patients with these specific antithrombin mutations.
authors.affiliation: Centro Regional de Hemodonación, Servicio de Hematología y Oncología Médica, Hospital Universitario Morales Meseguer, Regional Campus of International Excellence Campus Mare Nostrum, University of Murcia, Murcia, Spain.
authors.forename: Irene
authors.initials: I
authors.lastname: Martínez-Martínez
authors.forename: José
authors.initials: J
authors.lastname: Navarro-Fernández
authors.forename: Alice
authors.initials: A
authors.lastname: Østergaard
authors.forename: Ricardo
authors.initials: R
authors.lastname: Gutiérrez-Gallego
authors.forename: José
authors.initials: J
authors.lastname: Padilla
authors.forename: Nataliya
authors.initials: N
authors.lastname: Bohdan
authors.forename: Antonia
authors.initials: A
authors.lastname: Miñano
authors.forename: Cristina
authors.initials: C
authors.lastname: Pascual
authors.forename: Constantino
authors.initials: C
authors.lastname: Martínez
authors.forename: María Eugenia
authors.initials: ME
authors.lastname: de la Morena-Barrio
authors.forename: Sonia
authors.initials: S
authors.lastname: Aguila
authors.forename: Shona
authors.initials: S
authors.lastname: Pedersen
authors.forename: Søren Risom
authors.initials: SR
authors.lastname: Kristensen
authors.forename: Vicente
authors.initials: V
authors.lastname: Vicente
authors.forename: Javier
authors.initials: J
authors.lastname: Corral
mesh_terms: D000990:Antithrombin III / Q000235:genetics* / Q000378:metabolism*; D020152:Antithrombin III Deficiency / Q000235:genetics*; D001665:Binding Sites; D002846:Chromatography, Affinity; D004247:DNA / Q000235:genetics; D006493:Heparin / Q000378:metabolism*; D006579:Heterozygote; D006720:Homozygote; D006801:Humans; D007700:Kinetics; D008297:Male; D009030:Mosaicism; D009154:Mutation / Q000235:genetics*; D010375:Pedigree; D016133:Polymerase Chain Reaction; D011485:Protein Binding; D011487:Protein Conformation; D011499:Protein Processing, Post-Translational; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization; D013927:Thrombosis / Q000235:genetics* / Q000378:metabolism / Q000473:pathology
chemical_list: D000990:Antithrombin III; D006493:Heparin; D004247:DNA