Functional role of the polysaccharide component of rabbit thrombomodulin proteoglycan. Effects on inactivation of thrombin by antithrombin, cleavage of fibrinogen by thrombin and thrombin-catalysed activation of factor V.
Thrombomodulin (TM), a major anticoagulant protein at the vessel wall, serves as a potent cofactor for the activation of Protein C by thrombin. Previous work has indicated that (rabbit) TM is a proteoglycan that contains a single polysaccharide chain, tentatively identified as a sulphated galactosaminoglycan, and furthermore suggested that this component may be functionally related to additional anticoagulant activities expressed by the TM molecule [Bourin, Ohlin, Lane, Stenflo & Lindahl (1988) J. Biol. Chem. 263, 8044-8052]. Results of the present study establish that (enzymic) removal of the polysaccharide chain abolishes the inhibitory effect of TM on thrombin-induced fibrinogen clotting as well as the promoting effect of TM on the inactivation of thrombin by antithrombin, but does not affect the ability of TM to serve as a cofactor in the activation of Protein C. Studies of yet another biological activity of rabbit TM, namely the ability to prevent the activation of Factor V by thrombin [Esmon, Esmon & Harris (1982) J. Biol. Chem. 257, 7944-7947], confirmed that TM markedly delays the conversion of the native 330 kDa Factor V precursor into polypeptide intermediates, and further into the 96 kDa heavy chain and 71-74 kDa light-chain components of activated Factor Va. In contrast, the activation kinetics of a similar sample of Factor V incubated with thrombin in the presence of chondroitinase ABC-digested TM did not differ from that observed in the absence of TM. It is concluded that the inhibitory effect of TM on Factor V activation also depends on the presence of the polysaccharide component on the TM molecule.
Bourin
M C
MC
Department of Veterinary Medical Chemistry, Swedish University of Agricultural Sciences, Uppsala.
Lindahl
U
U
D000818:Animals; D000991:Antithrombins / Q000494:pharmacology*; D002808:Chondroitin Lyases / Q000378:metabolism; D004591:Electrophoresis, Polyacrylamide Gel; D005165:Factor V / Q000378:metabolism*; D015943:Factor Va / Q000378:metabolism; D005340:Fibrinogen / Q000378:metabolism*; D007700:Kinetics; D008168:Lung / Q000032:analysis; D011134:Polysaccharides / Q000378:metabolism; D011817:Rabbits; D011956:Receptors, Cell Surface / Q000302:isolation & purification / Q000378:metabolism / Q000494:pharmacology*; D018179:Receptors, Thrombin; D013329:Structure-Activity Relationship; D013917:Thrombin / Q000378:metabolism*
D000991:Antithrombins; D011134:Polysaccharides; D011956:Receptors, Cell Surface; D018179:Receptors, Thrombin; D015943:Factor Va; D005165:Factor V; D005340:Fibrinogen; D013917:Thrombin; D002808:Chondroitin Lyases