Fibrin glycosylation

Tissue plasminogen activator (tPA) is a protease with 527 amino acids and 4 glycosylation sites that acts in vivo as a thrombolytic agent. Its function is to proteolytically convert the zymogen, plasminogen, into active plasmin, which in turn degrades fibrin strands, thus dissolving the clots (Walsh, 2003). For this reason, recombinant tPA molecules... 

Plasminogen is the precursor of the serine protease plasmin which is involved in dissolution of fibrin clots and, hence, in removal of thrombi. The plasma concentration is about 12mg/100ml and the molecular mass 81 kDa. It contains 17.1% carbohydrate on two sites, one N-linked and one O-linked oligosaccharide. A variant is also known that is only 0-glycosylated. The structures of the oligosaccharides have been determined [71-73], and are shown in Fig. 11. 

The excess vessel wall fibrin accumulation and atherosclerosis seen as a long-term complication of diabetes may well result from the glycosylation-induced inhibition in fibrinogen (fibrin)-plasmin degradative function and heparin-catalyzed antithrombin III activity. 

B30. Brownlee, M., Vlassara, H., and Cerami, A., Nonenzymatic glycosylation reduces the su,sceptibility of fibrin to degradation by plasmin. Diabetes 32, 680-684 (1983). 

Mammalian cells produce two t-PA variants of N-linked glycosylation, type 1 (at asparagines 117,184, and 448) and type 2 (only as asparagines 117 and 448). The rate of fibrin-dependent plasminogen activation is two- to threefold faster for type 2 compared with type 1. The cDNA obtained from a human melanoma cell line was expressed in CHO cells to achieve glycosylation and a protein identical to the natural protein. Protein engineering studies have produced variant t-PA molecules with modified pharmacokinetics, affinity tor fibrin, catalytic activity, and side effects. 

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