Title :
N-glycans and the N
terminus of
protein C inhibitor affect the cofactor-enhanced rates of thrombin inhibition
Abstract :
- Protein C inhibitor ( PCI ) is a serine protease inhibitor, displaying broad protease specificity, found in blood and other tissues
- In blood, it is capable of inhibiting both procoagulant and anticoagulant proteases
- Mechanisms that provide specificity to PCI remain largely unrevealed
- In this study we have for the first time provided a full explanation for the marked size heterogeneity of blood-derived PCI and identified functional differences between naturally occurring PCI variants
- The heterogeneity was caused by differences in N-glycan structures , N-glycosylation occupancy, and the presence of a Delta6-N-cleaved form
- Bi-, tri-, and tetra-antennary complex N-glycans were identified
- Fucose residues were identified both on the core GlcNAc and as parts of sialyl-Le(a/x) epitopes
- Moreover, a glycan with a com position that implied a di-sialyl antenna was observed
- PCI was N-glycosylated at all three potential N-glycosylation sites, Asn-230, Asn-243, and Asn-319 , but a small fraction of PCI lacked the N-glycan at Asn-243
- The overall removal of N-glycans affected the maximal heparin- and thrombomodulin-enhanced rates of thrombin inhibition differently in different solution conditions
- In contrast, the Delta6-N-region increased both the heparin- and the thrombomodulin-enhanced rates of thrombin inhibition at all conditions examined
- These results thus demonstrate that the N-linked glycans and the N-terminal region of blood-derived PCI in different ways affect the cofactor-enhanced rates of thrombin inhibition and provide information on the mechanisms by which this may be achieved
- The findings are medically important, in view of the documented association of PCI with atherosclerotic plaques and the promising effect of PCI on reducing hypercoagulability states