| |
|
|
|
|
|
|
|||
|
B Lind, AH Johnsen and S Thorsen
Department of Clinical Biochemistry, Rigshospitalet, Copenhagen, Denmark.
The dysfunctional protein C from a thrombophilic patient heterozygote for a
G1388 to A converting the codon for Arg(-1) to His was purified from plasma
and characterized. N-terminal amino acid sequence analysis of the light
chain of the protein C demonstrated that the dysfunctional protein C is
elongated with one amino acid, namely the mutated His. This finding is
compatible with disruption by the mutated His of the original basic
propeptidase recognition sequence (Arg(-5)-Ile-Arg-Lys- Arg(-1)), resulting
in a shift of the cleavage site to a new position, Lys(-2)-His(-1), which
follows an alternative basic amino acid propeptidase recognition sequence
(Arg(-5)-Ile-Arg-Lys(-2)). Because the mutation affects the propeptide that
directs the gamma- carboxylation converting Glu to Gla residues in the Gla
domain, it was investigated whether the mutation impaired this reaction.
Gla fragment obtained by cleavage of the dysfunctional protein C light
chain with endoproteinase Asp-N was isolated by reverse-phase
high-performance liquid chromatography, methylated, and subjected to
N-terminal sequence analysis. The methylation step enabled the positive
identification of Gla residues as well as the determination of the relative
amount of Gla and Glu residues at each of the nine gamma-carboxylation
sites of the Gla domain. The analysis showed that all nine potential gamma-
carboxylation sites of the dysfunctional protein C were normally
carboxylated. This result is compatible with the notion that position - 1
is not a part of the recognition element for the gamma-carboxylase. In
conclusion, evidence is provided showing that the mutation leads to
aberrant propeptide processing and secretion of dysfunctional normally
carboxylated protein C extended with the mutated His.
This article has been cited by other articles:
| |||||||||||
| Copyright © 1997 by American Society of Hematology Online ISSN: 1528-0020 | |||||||||