Identification of Coagulation Factor VIII A2 Domain Residues Forming the Binding Epitope for Low-Density Lipoprotein Receptor-Related Protein
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- 作者：Andrey G. Sarafanov ; Evgeny M. Makogonenko ; Igor V. Pechik ; Klaus-Peter Radtke ; Alexey V. Khrenov ; Natalya M. Ananyeva ; Dudley K. Strickland ; and Evgueni L. Saenko
- 刊名：Biochemistry
- 出版年：2006
- 出版时间：February 14, 2006
- 年：2006
- 卷：45
- 期：6
- 页码：1829 - 1840
- 全文大小：4264K
- 年卷期：v.45,no.6(February 14, 2006)
- ISSN：1520-4995
文摘
Regulation of the coagulation factor VIII (fVIII) level in circulation involves a hepatic receptorlow-density lipoprotein receptor-related protein (LRP). One of two major LRP binding sites in fVIII islocated within the A2 domain (A2), likely exposed within the fVIII complex with von Willebrand factorand contributing to regulation of fVIII via LRP. This work aimed to identify A2 residues forming itsLRP-binding site, previously shown to involve residues 484-509. Isolated A2 was subjected to alanine-scanning mutagenesis followed by expression of a set of mutants in a baculovirus system. In competitionand surface plasmon resonance assays, affinities of A2 mutants K466A, R471A, R484A, S488A, R489A,R490A, H497A, and K499A for LRP were found to be decreased by 2-4-fold. This correlated with1.3-1.5-fold decreases in the degree of LRP-mediated internalization of the mutants in cell culture.Combining these mutations into pairs led to cumulative effects, i.e., 7-13-fold decrease in affinity forLRP and 1.6-2.2-fold decrease in the degree of LRP-mediated internalization in cell culture. We concludethat the residues mentioned above play a key role in formation of the A2 binding epitope for LRP.Experiments in mice revealed an ~4.5 times shorter half-life for A2 in the circulation in comparison withthat of fVIII. The half-lives of A2 mutant R471A/R484A or A2 co-injected with receptor-associated protein,a classical ligand of LRP, were prolonged by ~1.9 and ~3.5 times, respectively, compared to that of A2.This further confirms the importance of the mutated residues for interaction of A2 with LRP and suggeststhe existence of an LRP-dependent mechanism for removing A2 as a product of dissociation of activatedfVIII from the circulation.