title: Structural basis of the cofactor- and substrate-assisted activation of human coagulation factor IXa.
abstract: Human coagulation factor IX serves both to maintain and to control blood coagulation. The dual function of this hemophilic factor is implemented by a tiered activation mechanism. Processed two-chain factor IXa is catalytically silent; only together with its cofactor VIIIa does factor IXa form the highly potent Xase complex. The detailed mechanism of this secondary activation has remained elusive so far. Here we present the crystal structures of Xase-like factor IXa mutants with several-thousand-fold activity enhancement that mimic the secondary activation by Xase formation. The structures reveal how cofactor-triggered and substrate-assisted modulations in the factor IXa 99- and 60-loops cooperate in S4 through S2' formation, allowing for productive substrate recognition. We could further physically map and visualize a distinct communication line, along which agonists such as Ca(2+) direct their effects to the active site and vice versa.
authors.affiliation: Department of Molecular Biology, Division of Structural Biology, University of Salzburg, 5020 Salzburg, Austria.
authors.forename: Thomas
authors.initials: T
authors.lastname: Zögg
authors.affiliation: Department of Molecular Biology, Division of Structural Biology, University of Salzburg, 5020 Salzburg, Austria. Electronic address: Hans.Brandstetter@sbg.ac.at.
authors.forename: Hans
authors.initials: H
authors.lastname: Brandstetter
mesh_terms: D000590:Amino Acid Chloromethyl Ketones / Q000378:metabolism; D020816:Amino Acid Motifs; D001665:Binding Sites; D002118:Calcium / Q000378:metabolism; D020134:Catalytic Domain; D018360:Crystallography, X-Ray; D003546:Cysteine Endopeptidases / Q000737:chemistry / Q000378:metabolism; D019855:Ethylene Glycol / Q000378:metabolism; D015949:Factor IXa / Q000037:antagonists & inhibitors / Q000737:chemistry* / Q000378:metabolism*; D015944:Factor VIIIa / Q000737:chemistry / Q000378:metabolism; D006801:Humans; D006860:Hydrogen Bonding; D008954:Models, Biological; D008958:Models, Molecular; D050505:Mutant Proteins / Q000737:chemistry; D009363:Neoplasm Proteins / Q000737:chemistry / Q000378:metabolism; D011487:Protein Conformation; D012964:Sodium / Q000378:metabolism
chemical_list: D000590:Amino Acid Chloromethyl Ketones; D050505:Mutant Proteins; D009363:Neoplasm Proteins; C086298:glutamyl-glycyl-arginyl-chloromethyl ketone; D015944:Factor VIIIa; D012964:Sodium; D015949:Factor IXa; D003546:Cysteine Endopeptidases; C030910:cancer procoagulant; D019855:Ethylene Glycol; C040308:phenylalanyl-prolyl-arginine-chloromethyl ketone; D002118:Calcium