Functional consequences of the Ser334-->Pro mutation in a human factor X variant (factor XMarseille).
A factor X molecular variant was identified in a 55-year-old woman at a routine preoperative coagulation screening. Plasma factor X antigen was normal, whereas factor X activity was decreased when factor X was activated by either the extrinsic pathway (21%), the intrinsic pathway (21%) or the factor X activator from Russell viper venom, RVV-X (26%). Factor XMarseille was isolated from plasma by immunoaffinity chromatography and compared with normal factor X purified by the same method. Activation of factor XMarseille by factor IXa or by RVV-X in a purified system showed that the rate of cleavage was decreased, whereas once produced, factor XaMarseille had a normal catalytic efficiency for either the peptide substrate S-2765 (D-Arg-Gly-Arg-NH-Np) or prothrombin. The rate of inhibition of factor XaMarseille by antithrombin III was also normal. Defective proteolysis of factor XMarseille by factor IXa or by RVV-X was the consequence of a threefold decrease in the kcat for the activation of factor XMarseille while the Km of RVV-X or factor IXa for factor X was normal. We have determined the molecular basis of the defect in the factor XMarseille gene by amplification of all eight exons, single-strand conformational polymorphism analysis of the amplified exons and subsequent sequence analysis. The patient was homozygous for a T-->C mutation in exon VIII, resulting in the substitution of Ser334 by proline. From comparison of three-dimensional models of various serine proteases, it appears that Ser334 is located within a surface-exposed variable region of factor X. This observation suggests that the Ser334-->Pro mutation either is responsible for a misalignment of the active sites of specific factor X activators in close proximity to the cleavage site, or that the Ser-->Pro mutation alters the spatial orientation of the cleavage site by nonlocal modifications of factor X structure.
Laboratoire de Recherche sur l'Hémostase et la Thrombose, Faculté Xavier Bichat, Paris, France.
A
A
Bezeaud
T
T
Miyata
D
D
Helley
Y Z
YZ
Zeng
H
H
Kato
M F
MF
Aillaud
I
I
Juhan-Vague
M C
MC
Guillin
D000818:Animals; D001483:Base Sequence; D002118:Calcium / Q000378:metabolism; D002417:Cattle; D004247:DNA; D017931:DNA Primers; D015943:Factor Va / Q000378:metabolism; D005170:Factor X / Q000235:genetics / Q000378:metabolism*; D005171:Factor X Deficiency / Q000097:blood; D015951:Factor Xa / Q000378:metabolism; D005260:Female; D006801:Humans; D008875:Middle Aged; D008969:Molecular Sequence Data; D010743:Phospholipids / Q000378:metabolism; D017354:Point Mutation; D011392:Proline / Q000235:genetics*; D011516:Prothrombin / Q000378:metabolism; D011817:Rabbits; D012694:Serine / Q000235:genetics*
D017931:DNA Primers; D010743:Phospholipids; D012694:Serine; D015943:Factor Va; D011516:Prothrombin; D005170:Factor X; D004247:DNA; D011392:Proline; D015951:Factor Xa; D002118:Calcium