Thromb Haemost 2009; 102(04): 645-655
DOI: 10.1160/TH09-03-0152
Blood Coagulation, Fibrinolysis and Cellular Haemostasis
Schattauer GmbH

Identification of a protein S-interactive site within the A2 domain of the factor VIII heavy chain

Masahiro Takeyama
1   Department of Pediatrics, Nara Medical University, Kashihara, Nara, Japan
,
Keiji Nogami
1   Department of Pediatrics, Nara Medical University, Kashihara, Nara, Japan
,
Evgueni L. Saenko
2   Department of Biochemistry and Molecular Biology, University of Maryland School of Medicine, Baltimore, Maryland, USA
,
Katsumi Nishiya
1   Department of Pediatrics, Nara Medical University, Kashihara, Nara, Japan
,
Kenichi Ogiwara
1   Department of Pediatrics, Nara Medical University, Kashihara, Nara, Japan
,
Midori Shima
1   Department of Pediatrics, Nara Medical University, Kashihara, Nara, Japan
› Author Affiliations

Financial support: This work was partly supported by grants for MEXT KAKENHI (19591264) and The Mother and Child Health Foundation. An account of this work was presented at the 49th annual meeting of the American Society of Hematology, December 8, 2007, Atlanta, Georgia, USA.
Further Information

Publication History

Received: 11 March 2009

Accepted after major revision: 23 June 2009

Publication Date:
24 November 2017 (online)

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Summary

We have recently demonstrated that protein S impairs the intrinsic tenase complex, independent of activated protein C, in competitive interactions between the A2 and A3 domains of factor VIIIa and factor IXa. In the present study, we have identified a protein S-interactive site in the A2 domain of factor VIIIa. Anti-A2 monoclonal antibody recognising a factor IXa-functional region (residues 484–509) on A2, and synthetic peptide inhibited the A2 binding to protein S by ∼60% and ∼70%, respectively, in solid-phase binding assays. The 484–509 peptide directly bound to protein S dose-dependently. Covalent cross-linking was observed between the 484–509 peptide and protein S following reaction with EDC (1-ethyl-3-(3-dimethylaminopropyl)-carbodiimide). The cross-linked adduct was consistent with 1:1 stoichiometry of reactants. Cross-linking formation was blocked by addition of the 484–497 peptide, but not by the 498–509 peptide. Furthermore, N-terminal sequence analysis of the 484–509 peptide-protein S adduct showed that three sequential residues (S488, R489, and R490) in A2 were not identified, suggesting that these residues participate in cross-link formation. Mutant A2 molecules where these residues were converted to alanine were evaluated for the binding of protein S. The S488A, R489A, and R490A mutants demonstrated ∼four-fold lower affinity than wild-type A2.These results indicate that the 484–509 region in the A2 domain of factor VIIIa, in particular sequential residues at positions 488–490, contributes to a unique protein S-interactive site.