Carbohydrate moieties on the procofactor factor V, but not the derived cofactor factor Va, regulate its inactivation by activated protein C

Comprehensive N- and O-glycosylation mapping of human coagulation factor V

BACKGROUND/OBJECTIVE

Coagulation factor V (FV), a multidomain glycoprotein, is an essential cofactor in the blood clotting cascade. FV deficiency is a rare bleeding disorder that results in poor clotting after an injury or surgery. The only treatment for the disease is infusions of fresh frozen plasma and blood platelets. Glycosylation affects the biological activity, pharmacokinetics, immunogenicity, and in vivo clearance rate of proteins in the plasma. The glycan profile of FV, as well as how it affects the activity, stability, and immunogenicity, remains unknown.

METHODS

In this study, we comprehensively mapped the glycosylation patterns of human plasma-derived FV by combining multienzyme digestion, hydrophilic interaction chromatography enrichment of glycopeptides, and alternated fragmentation mass spectrometry analysis.

RESULTS/CONCLUSION

A total of 57 unique N-glycopeptides and 51 O-glycopeptides were identified, which were categorized into 40 N-glycan and 17 O-glycan compositions. Such glycosylation details are fundamental for future functional studies and therapeutics development. In addition, the established methodology can be readily applied to analyze glycosylation patterns of proteins with more than 2000 amino acids.

The anticoagulant function of coagulation factor V

Almost two decades ago an anticoagulant function of factor V (FV) was discovered, as an anticoagulant cofactor for activated protein C (APC). A natural mutant of FV in which the R506 inactivation site was mutated to Gln (FVLeiden) was inactivated slower by APC, but also could not function as anticoagulant cofactor for APC in the inactivation of activated factor VIII (FVIIIa). This mutation is prevalent in populations of Caucasian descent, and increases the chance of thrombotic events in carriers. Characterisation of the FV anticoagulant effect has elucidated multiple properties of the anticoagulant function of FV: 1) Cleavage of FV at position 506 by APC is required for anticoagulant function. 2) The C-terminal part of the FV B domain is required and the B domain must have an intact connection with the A3 domain of FV. 3) FV must be bound to a negatively charged phospholipid membrane. 4) Protein S also needs to be present. 5) FV acts as a cofactor for inactivation of both FVa and FVIIIa. 6) The prothrombotic function of FVLeiden is a function of both reduced APC cofactor activity and resistance of FVa to APC inactivation. However, detailed structural and mechanistic properties remain to be further explored.

α(1,3)-Fucosyltransferases FUT4 and FUT7 control murine susceptibility to thrombosis

The α(1,3)-fucosyltransferases, types IV and VII (FUT4 and FUT7, respectively), are required for the synthesis of functional selectin-type leukocyte adhesion molecule ligands. The selectins and their ligands modulate leukocyte trafficking, and P-selectin and its ligand, P-selectin glycoprotein ligand-1, can modulate hemostasis and thrombosis. Regulation of thrombosis by FUT4 and/or FUT7 activity was examined in mouse models of carotid artery thrombosis and collagen/epinephrine-induced thromboembolism. Mice lacking both FUT4 and FUT7 (Fut(-/-) mice) had a shorter time to occlusive thrombus formation in the injured carotid artery and a higher mortality due to collagen/epinephrine-induced pulmonary thromboemboli. Mice lacking P-selectin or P-selectin glycoprotein ligand-1 did not have a prothrombotic phenotype. Whole blood platelet aggregation was enhanced, and plasma fibrinogen content, clot weight, and clot strength were increased in Fut(-/-) mice, and in vitro clot lysis was reduced compared with wild type. Fut4(-/-), but not Fut7(-/-), mice had increased pulmonary thromboembolism-induced mortality and decreased thromboemboli dissolution in vivo. These data show that FUT4 and FUT7 activity regulates thrombosis in a P-selectin- and P-selectin glycoprotein ligand-1-independent manner and suggest that FUT4 activity is important for thrombolysis.

Carbohydrates and activity of natural and recombinant tissue factor

The effect of glycosylation on tissue factor (TF) activity was evaluated, and site-specific glycosylation of full-length recombinant TF (rTF) and that of natural TF from human placenta (pTF) were studied by liquid chromatography-tandem mass spectrometry. The amidolytic activity of the TF.factor VIIa (FVIIa) complex toward a fluorogenic substrate showed that the catalytic efficiency (V(max)) of the complex increased in the order rTF(1-243) (Escherichia coli) < rTF(1-263) (Sf9 insect cells) < pTF for the glycosylated and deglycosylated forms. Substrate hydrolysis was unaltered by deglycosylation. In FXase, the K(m) of FX for rTF(1-263)-FVIIa remained unchanged after deglycosylation, whereas the k(cat) decreased slightly. A pronounced decrease, 4-fold, in k(cat) was observed for pTF.FVIIa upon deglycosylation, whereas the K(m) was minimally altered. The parameters of FX activation by both rTF(1-263D)-FVIIa and pTF(D)-FVIIa were identical and similar to those for rTF(1-243)-FVIIa. In conclusion, carbohydrates significantly influence the activity of TF proteins. Carbohydrate analysis revealed glycosylation on asparagines 11, 124, and 137 in both rTF(1-263) and pTF. The carbohydrates of rTF(1-263) contain high mannose, hybrid, and fucosylated glycans. Natural pTF contains no high mannose glycans but is modified with hybrid, highly fucosylated, and sialylated sugars.

Gingipain-dependent interactions with the host are important for survival of Porphyromonas gingivalis

Porphyromonas gingivalis, a major periodontal pathogen, must acquire nutrients from host derived substrates, overcome oxidative stress and subvert the immune system. These activities can be coordinated via the gingipains which represent the most significant virulence factor produced by this organism. In the context of our contribution to this field, we will review the current understanding of gingipain biogenesis, glycosylation, and regulation, as well as discuss their role in oxidative stress resistance and apoptosis. We can postulate a model, in which gingipains may be part of the mechanism for P. gingivalis virulence.

Identification of the N-linked glycosylation sites of vitamin K-dependent carboxylase and effect of glycosylation on carboxylase function

The vitamin K-dependent carboxylase is an integral membrane protein which is required for the post-translational modification of a variety of vitamin K-dependent proteins. Previous studies have suggested carboxylase is a glycoprotein with N-linked glycosylation sites. In this study, we identify the N-glycosylation sites of carboxylase by mass spectrometric peptide mapping analyses combined with site-directed mutagenesis. Our mass spectrometric results show that the N-linked glycosylation in carboxylase occurs at positions N459, N550, N605, and N627. Eliminating these glycosylation sites by changing asparagine to glutamine caused the mutant carboxylase to migrate faster on SDS-PAGE gels, adding further evidence that these sites are glycosylated. In addition, the mutation studies identified N525, a site that cannot be recovered by mass spectroscopy analysis, as a glycosylation site. Furthermore, the potential glycosylation site at N570 is glycosylated only if all five natural glycosylation sites are simultaneously mutated. Removal of the oligosaccharides by glycosidase from wild-type carboxylase or by elimination of the functional glycosylation sites by site-directed mutagenesis did not affect either the carboxylation or epoxidation activity when the small FLEEL pentapeptide was used as a substrate, suggesting that N-linked glycosylation is not required for the enzymatic function of carboxylase. In contrast, when site N570 and the five natural glycosylation sites were mutated simultaneously, the resulting carboxylase protein was degraded. Our results suggest that N-linked glycosylation is not essential for carboxylase enzymatic activity but is important for protein folding and stability.

Elucidation of N-glycosylation sites on human platelet proteins: a glycoproteomic approach

Among known platelet proteins, a prominent and functionally important group is represented by glycoprotein isoforms. They account e.g. for secretory proteins and plasma membrane receptors including integrins and glycoprotein VI as well as intracellular components of cytosol and organelles including storage proteins (multimerin 1 etc.). Although many of those proteins have been studied for some time with regard to their function, little attention has been paid with respect to their glycosylation sites. Here we report the analysis of N-glycosylation sites of human platelet proteins. For the enrichment of glycopeptides, lectin affinity chromatography as well as chemical trapping of protein bound oligosaccharides was used. Therefore, concanavalin A was used for specific interaction with carbohydrate species along with periodic acid oxidation and hydrazide bead trapping of glycosylated proteins. Derivatization by peptide:N-glycosidase F yielded deglycosylated peptides, which provided the basis for the elucidation of proteins and their sites of modification. Using both methods in combination with nano-LC-ESI-MS/MS analysis 70 different glycosylation sites within 41 different proteins were identified. Comparison with the Swiss-Prot database established that the majority of these 70 sites have not been specifically determined by previous research projects. With this approach including hydrazide bead affinity trapping, the immunoglobulin receptor G6f, which is known to couple to the Ras-mitogen-activated protein kinase pathway in the immune system, was shown here for the first time to be present in human platelets.