Maintenance of ribosomal protein S19 in plasma by complex formation with prothrombin.

We have demonstrated that the cross-linking of ribosomal protein S19 (RP S19) on platelets by activated factor XIII provides chemotactic potency to monocytes/macrophages for a resolution of coagulum. Factor XIII is activated by an active form of prothrombin, thrombin. We here report that RP S19 is present as a complex with prothrombin in the blood stream. Formation of this complex was blocked by a mutation of the glycosaminoglycan-binding basic cluster (Lys(23) -Lys(29) ) in RP S19. Prothrombin-RP S19 interaction was enhanced by an absence of Ca(2+) and the plasma RP S19 concentration was significantly low in the patient treated with warfarin, indicating participation of the γ-carboxyl glutamic acid domain of prothrombin making a salt bridge with the basic cluster. The complex formation likely explains why a protein as small as RP S19 can prevent from a filtering system of renal glomeruli at a steady state. The translocation of RP S19 from prothrombin to platelets during blood coagulation seems to be also advantageous for RP S19 from the perspective of oligomerisation by activated factor XIII, which should have been activated by thrombin.