title: Crystal structures of the FXIa catalytic domain in complex with ecotin mutants reveal substrate-like interactions.
abstract: Thrombosis can lead to life-threatening conditions such as acute myocardial infarction, pulmonary embolism, and stroke. Although commonly used anti-coagulant drugs, such as low molecular weight heparin and warfarin, are effective, they carry a significant risk of inducing severe bleeding complications, and there is a need for safer drugs. Activated Factor XI (FXIa) is a key enzyme in the amplification phase of the coagulation cascade. Anti-human FXI antibody significantly reduces thrombus growth in a baboon thrombosis model without bleeding problems (Gruber, A., and Hanson, S. R. (2003) Blood 102, 953-955). Therefore, FXIa is a potential target for anti-thrombosis therapy. To determine the structure of FXIa, we derived a recombinant catalytic domain of FXI, consisting of residues 370-607 (rhFXI370-607). Here we report the first crystal structure of rhFXI370-607 in complex with a substitution mutant of ecotin, a panserine protease protein inhibitor secreted by Escherichia coli, to 2.2 A resolution. The presence of ecotin not only assisted in the crystallization of the enzyme but also revealed unique structural features in the active site of FXIa. Subsequently, the sequence from P5 to P2' in ecotin was mutated to the FXIa substrate sequence, and the structures of the rhFXI370-607-ecotin mutant complexes were determined. These structures provide us with an understanding of substrate binding interactions of FXIa, the structural information essential for the structure-based design of FXIa-selective inhibitors.
authors.affiliation: Daiichi Asubio Medical Research Laboratories LLC, Cambridge, Massachusetts 02139, USA. lei.jin@daiamed.com
authors.forename: Lei
authors.initials: L
authors.lastname: Jin
authors.forename: Pramod
authors.initials: P
authors.lastname: Pandey
authors.forename: Robert E
authors.initials: RE
authors.lastname: Babine
authors.forename: Joan C
authors.initials: JC
authors.lastname: Gorga
authors.forename: Katherine J
authors.initials: KJ
authors.lastname: Seidl
authors.forename: Ellen
authors.initials: E
authors.lastname: Gelfand
authors.forename: David T
authors.initials: DT
authors.lastname: Weaver
authors.forename: Sherin S
authors.initials: SS
authors.lastname: Abdel-Meguid
authors.forename: James E
authors.initials: JE
authors.lastname: Strickler
mesh_terms: D000925:Anticoagulants / Q000737:chemistry; D001665:Binding Sites; D020134:Catalytic Domain; D002851:Chromatography, High Pressure Liquid; D018360:Crystallography, X-Ray / Q000379:methods*; D019281:Dimerization; D004926:Escherichia coli / Q000378:metabolism; D029968:Escherichia coli Proteins / Q000737:chemistry*; D015945:Factor XIa / Q000737:chemistry*; D006801:Humans; D008958:Models, Molecular; D009154:Mutation; D033903:Periplasmic Proteins / Q000737:chemistry*; D011485:Protein Binding; D011487:Protein Conformation; D017434:Protein Structure, Tertiary; D011994:Recombinant Proteins / Q000737:chemistry; D012306:Risk; D012694:Serine / Q000737:chemistry; D013237:Stereoisomerism; D013927:Thrombosis
chemical_list: D000925:Anticoagulants; C039076:Eco protein, E coli; D029968:Escherichia coli Proteins; D033903:Periplasmic Proteins; D011994:Recombinant Proteins; D012694:Serine; D015945:Factor XIa