Molecular defect in coagulation factor XFriuli results from a substitution
of serine for proline at position 343
HL James, A Girolami and DS Fair
Department of Biochemistry, University of Texas Health Center, Tyler 75710.
Our previous findings suggested that coagulation factor XFriuli could be
functionally defective owing to a point mutation in the portion of the
factor X gene coding for the fully activated heavy chain. To verify the
existence of this postulated change, we analyzed all eight exons of the
normal and Friuli factor X gene. Each exon was amplified from genomic DNA
using the polymerase chain reaction and cloned into the plasmid pUC19. The
amplified DNA inserts were subjected to direct sequencing by the dideoxy
chain termination method with forward and reverse oligonucleotide
sequencing primers. A point mutation (C to T transition at nucleotide
position 19,297) that results in coding for serine (TCC) in place of
proline (CCC) at amino acid position 343 was found. This substitution
involves a highly conserved proline residue oriented spatially close to
both the cleavage site of the zymogen and the active site of the enzyme and
explains the previous observations of discrete biochemical and functional
differences between factor XFriuli and normal factor X. The mutation
abolished an HgiCI restriction site present in the normal factor X gene,
and this change constitutes the basis for a convenient method for screening
individuals carrying this molecular defect. Proline343 is in conserved
region 5 of the serine protease superfamily to which factor X belongs and
is part of a 14- residue L*****P******C motif that occurs in at least 16
other enzymes. Computer analysis suggests that the motif may be an
essential aspect of conformational features important to functional
properties of factor X as well as other serine proteases.
Volume 77,
Issue 2,
pp. 317-323,
01/15/1991
Copyright © 1991 by The American Society of Hematology
