Antithrombin Murcia (K241E) causing antithrombin deficiency: a possible role for altered glycosylation.
BACKGROUND
Identification of mutations in the SERPINC1 gene has revealed different mechanisms responsible for antithrombin deficiency. Deletions and nonsense mutations associate with type I deficiency. Certain missense mutations cause type II deficiency by affecting the heparin binding site or the reactive center loop, while others result in type I deficiency by intracellular retention or RNA instability.


METHODS
We studied the molecular, biochemical, proteomic and glycomic characterization of a new natural mutant (K241E) that may be classified as pleiotropic.


RESULTS
The mutation caused a significant decrease in the anticoagulant activity mainly due to a reduced heparin affinity and a modification of the electrostatic potential that might explain the impaired ability of the mutant protein to form complexes with the target protease in the absence of heparin. Mass spectrometry and glycomic analyses confirmed an increased molecular weight of 800 Da in the mutant protein possibly due to core-fucosylation, provoking the loss of heparin affinity. Additionally, carriers of this mutation also have a minor mutant isoform that still followed normal glycosylation, retaining similar heparin affinity to wild-type alpha-antithrombin, and certain anticoagulant activity, which may explain the milder thrombotic risk of patients carrying this mutation. Similar results were observed using recombinant K241E antithrombin molecules.


CONCLUSIONS
Our data suggest a new mechanism involved in antithrombin type II deficiency by indirectly affecting the glycosylation of a natural variant. Additional studies are required to confirm this hypothesis.
Martínez-Martínez
Irene
I
University of Murcia, Centro Regional de Hemodonación, Murcia 30003, Spain.
Ordóñez
Adriana
A
Navarro-Fernández
José
J
Pérez-Lara
Angel
A
Gutiérrez-Gallego
Ricardo
R
Giraldo
Rafael
R
Martínez
Constantino
C
Llop
Esther
E
Vicente
Vicente
V
Corral
Javier
J
D000328:Adult; D019943:Amino Acid Substitution; D000990:Antithrombin III / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D020152:Antithrombin III Deficiency / Q000235:genetics*; D001483:Base Sequence; D015153:Blotting, Western; D005260:Female; D020022:Genetic Predisposition to Disease / Q000235:genetics*; D006031:Glycosylation; D006801:Humans; D008297:Male; D008958:Models, Molecular; D009154:Mutation; D010375:Pedigree; D011487:Protein Conformation
C542513:SERPINC1 protein, human; D000990:Antithrombin III