Characterization of the functional defect in factor IX Alabama. Evidence for a conformational change due to high affinity calcium binding in the first epidermal growth factor domain.

摘要: Factor IX Alabama is a factor variant in which glycine has been substituted for Asp47 the first epidermal growth (EGF) domain. The structural defect results molecule with 10% of normal coagulant activity. interactions immunoaffinity-purified its activator, cofactors, and substrate have investigated to determine functional variant. activated by XIa/calcium at near rates. Calcium fluorescence-quenching experiments indicate that high affinity calcium binding EGF domain not altered Alabama. active site IXa fully competent activate X absence when using polylysine as surface catalyze reaction. only 64% activity presence 300 microM CaCl2 polylysine-catalyzed system although apparent constants are similar. 52-60% calcium/phospholipid vesicle system. addition VIIIa phospholipid decreases relative rate 18-19% normal. Three-dimensional computer-aided models no major alterations resulting from substitution Asp47. model predicts calcium-binding involving Asp47, Asp49, Asp64, Asp65. Our data, however, necessary form site. We conclude coordinates bound calcium, inducing conformational change essential proper interaction VIIIa.