Portal de Periódicos da CAPES

Factor IX Zutphen: a Cys18→Arg mutation results in formation of a heterodimer with α 1-microglobulin and the inability to form a calcium-induced conformation

1995; Portland Press; Volume: 311; Issue: 3 Linguagem: Inglês

10.1042/bj3110753

1470-8728

E G C Wojcik, Marieke van den Berg, I K van der Linden, S R Poort, R Cupers, Rogier M. Bertina,

Coagulation, Bradykinin, Polyphosphates, and Angioedema

Factor IX Zutphen is a variant factor IX molecule isolated from the blood of a patient with severe haemophilia B. The molecular defect in factor IX Zutphen is a Cys18-->Arg mutation as a result of a T-->C transition at residue 6427 of the factor IX gene of the patient. The mutation disrupts the disulphide bond in the Gla-domain between Cys18 and Cys23. The remaining free cysteine residue results in the formation of a 95 kDa complex with alpha 1-microglobulin through an intermolecular disulphide bond. The same complex circulates at high levels in plasma of carriers of the mutation. The variant molecule has a calcium-binding defect, which is shown not to be caused by incomplete gamma-carboxylation. Factor IX Zutphen can not bind to phospholipids and can not be activated by factor XIa or by factor VIIa-tissue factor complex. Two sequential metal ion-dependent conformational transitions (factor IX-->factor IX′-->factor IX*) have been proposed for human factor IX [Liebman (1987) J. Biol. Chem. 262, 7605-7612], based upon the metal ion requirements for binding to anti-factor IX:Mg(II) antibodies, which are specific for the factor IX′ conformation, and anti-factor IX:Ca(II) antibodies, which are specific for the factor IX* conformation. We used these conformation-specific antibodies, and antibodies raised against a synthetic peptide corresponding to residues 35-50 of human factor IX [anti-factor IX(35-50)] to study the metal ion-induced conformation of factor IX Zutphen. The disruption of the disulphide bond in the Gla-domain, maybe in combination with the complex with alpha 1-microglobulin, destabilized the factor IX′ conformation. The formation of the factor IX* conformation was prevented independent of the presence of alpha 1-microglobulin. The disulphide bond in the Gla-domain is therefore essential for the calcium-dependent conformation and function of factor IX.