Role of high-molecular-weight kininogen in surface-binding and activation of coagulation Factor XI and prekallikrein.

Abstract

In the contact phase of activation of the kinin-forming, intrinsic clotting, and fibrinolytic systems, high-molecular-weight kininogen acts as a cofactor for the activation of Factor XI, prekallikrein, and Hageman factor. One mechanism by which high-molecular-weight kininogen acts as a cofactor has been studied by using 125f-labeled Factor XI and prekallikrein in kaolin-activated normal human plasma and plasmas deficient in high-molecular-weight kininogen and Hageman factor. High-molecular-weight kininogen was found to be essential for normal binding and cleavage of both Factor XI and prekallikrein on the kaolin surface. Hageman factor was essential for cleavage but not for binding of Factor XI and prekallikrein to kaolin. In normal plasma 80% of the activated Factor XI remained surface-bound, whereas 80% of the kallikrein was not surface-bound. These findings are consistent with the hypothesis that, in the initial phase of contact activation, high-molecular-weight kininogen links both Factor XI and prekallikrein to the exposed surface where they are activated by surface-bound activated Hageman factor. Once activated, the Factor XI molecules remain localized at the site of activation, in contrast to the kallikrein molecules which are found largely in the surrounding plasma.Activation of Hageman factor (Factor XII) upon a negatively charged surface initiates intrinsic coagulation, fibrinolysis, and the generation of vasoactive peptides (1-5). High-molecularweight (Mr) kininogen is a cofactor for the optimal activation of surface-bound Hageman factor by kallikrein (6-8) and for the activation of prekallikrein and Factor XI by surface-bound activated Hageman factor (6-8). Prekallikrein is complexed to high Mr kininogen in plasma (9). Recent studies (10; R. C. Wiggins, B. N. Bouma, C. G. Cochrane, and J. H. Griffin, unpublished data) suggest that Factor XI is also complexed to high Mr kininogen in plasma. In this study we demonstrate that one mechanism by which high Mr kininogen acts as a cofactor for the activation of both Factor XI and prekallikrein in plasma is to bind both these molecules to the surface where they are activated by surface-bound activated Hageman factor. We also demonstrate that, while activated Factor XI remains associated with the surface, kallikrein dissociates from the surface. MATERIALS AND METHODS Purified proteinsFactor XI was isolated from normal human plasma as described elsewhere (11) and was determined to be more than 95% homogeneous on sodium dodecyl sulfate (NaDodSO4/polyacrylamide gels. The purified protein had a specific clotting activity of 220 units/mg, where 1 clotting unit is defined as the amount of activity present in 1 ml of citrated normal human plasma. Factor XI was radiolabeled with '25iodine by the insolubilized lactoperoxidase method (12). The 125I-labeled Factor XI (125I-Factor XI), 5 ,uCi/,ug, retained its procoagulant activities at 3.6 clotting units/ml.Prekallikrein was isolated from normal human plasma by a method similar to that described for Factor XI (11...

Kininogen deficiency protects from ischemic neurodegeneration in mice by reducing thrombosis, blood-brain barrier damage, and inflammation

“…Second, this apparent contradiction suggests potentially novel mechanisms by which KNG promotes thrombosis, which at this point are unknown. Although these may involve FXI, which binds highmolecular-weight KNG, [29][30][31] whether these interactions alone account for the prothrombotic activity of KNG is uncertain. Third, the degree of neuroprotection caused by KNG depletion is remarkable and exceeds that observed in other reports of cerebral ischemia in animals deficient in members of the kallikrein-kinin system.…”

Activation of Rabbit Hageman Factor by Homogenates of Cultured Rabbit Endothelial Cells

“…However, if the HF-cleaving activity is exposed when EC or deeper layers are damaged, HF activation should occur. Furthermore, damage to the EC layer might expose subcellular structures with a sufficient density of negative charges to facilitate assembly of the surfacebound HF-high Mr kininogen-Factor XI-prekallikrein complexes similar to the one demonstrated for kaolin (12,39,40). Under these circumstances, the EC enzyme could initiate HF cleavage, an essential step for the reciprocal activation between HF and prekallikrein (41).…”

“…The finding that, in the presence of kaolin and high Mr kininogen, Factor XI could also be activated by EC-generated HFa is consistent with our observation that kaolin-bound HF was cleaved by the EC extract to yield the 52,000 and 28,000 Mr fragments of the surface-bound a-HFa. The marked requirement for high Mr kininogen for Factor XI activation emphasizes the role of this cofactor molecule in placing the Factor XI on an appropriate surface where it can be activated by a-HFa (12,39).…”

“…The specific clotting activity was 1.6-fold greater than that of single-chain HF. Prekallikrein (kindly provided by Dr. Richard Ulevitch, Research Institute of Scripps Clinic), Factor XI, and high M; kininogen were purified from citrated rabbit plasma as previously reported (10)(11)(12). Factor XI and prekallikrein migrated as homogeneous single-protein bands on SDS-PAGE in the presence and absence of reducing agents.…”

Identification of [hydroxyproline3]‐lysyl‐bradykinin released from human kininogens by human urinary kallikrein

“…However, since the amount of hydroxyproline acquired into the procollagen chains is required for formation of the typical triple helix structure of functional collagen [ 161, hydroxylation of proline in kininogen precursors might similarly influence the conformation and function of the secreted proteins. in this context, it could be speculated that such a hydroxylation might also influence the versatile functions of kininogens in serving as a cofactor in contact activation of the Hageman factor-dependent pathways [20] or as thiol protease inhibitors [21,22] in addition to being the kinin precursors.…”