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PubMed1996

Autoantibodies to kininogen-phosphatidylethanolamine complexes augment thrombin-induced platelet aggregation.

Autoantibodies to the zwitterionic phospholipid (PL), phosphatidylethanolamine (PE), have been described in patients with thrombotic disease. We have reported that certain anti-PE antibodies (aPE) are not specific for PE, but are directed to PE-binding plasma proteins, high molecular weight kininogen (HK) and low molecular weight kininogen (LK). Kininogens bind to platelets and inhibit thrombin-induced platelet aggregation. This inhibition is specific for thrombin because kininogens do not inhibit platelet aggregation induced by adenosine diphosphate (ADP), collagen or calcium ionophore. To date, a platelet kininogen receptor has not been described. We recently reported that purified kininogens bind to purified PE in vitro. This opens the possibility that kininogens can bind to platelets by virtue of exposed PE in the platelet membrane. We thus questioned if aPE can recognize platelet bound kininogens and negate their antithrombotic property. Our experiments support this possibility by demonstrating that exogenously added kininogen-dependent IgG aPE markedly increased thrombin-induced platelet aggregation in vitro but did not alter ADP-induced aggregation. In contrast, kininogen independent IgG aPE which recognized PE per se did not augment thrombin-induced platelet aggregation. These data support a hypothesis that kininogen dependent aPE may cause thrombosis in vivo due to disruption of the normal antithrombotic effects of kininogen.

Animals↗
PubMed1992

Differential regulation of kininogen gene expression by estrogen and progesterone in vivo.

Kininogens which have multifunctional domains, serve as the precursors of potent vasoactive kinin peptides and also function as cysteine proteinase inhibitors. Given its potential role in blood pressure homeostasis and inflammation, we have examined the regulation of rat kininogen gene expression by sex hormones in vivo. Our studies indicate a differential regulation of kininogen gene expression in rat liver by estrogen and progesterone. Northern and dot blot analysis using a rat low molecular weight kininogen cDNA probe show that kininogen mRNA levels in the liver of female rats are 4-fold higher than those in male rats. Ovariectomy results in a reduction of kininogen transcripts in the liver, while estradiol replacement of the ovariectomized rats increases kininogen mRNA levels. Similarly, Northern blot analysis using a kallikrein cDNA probe shows that estradiol treatment induces an increase of kallikrein gene expression in the kidney of the same animals. In contrast, progesterone treatment of the ovariectomized rats results in an increase in renal kallikrein mRNA levels while it reduces kininogen gene expression as compared to vehicle-treated ovariectomized animals. Immunoreactive kininogen levels in the serum, analyzed by a direct radioimmunoassay and Western blot, are increased by estradiol but slightly decreased by progesterone treatment. Western blot of serum proteins on a two-dimensional polyacrylamide gel reveals that in estradiol-treated ovariectomized rats, the levels of several 68,000 Da kininogens varying in charge are markedly higher than those in ovariectomized rats. The results indicate that estrogen is one of the determinants in regulating low molecular weight kininogen gene expression in vivo. The impact of estrogen-regulated kininogen expression on cardiovascular function awaits further investigation.

Animals↗
PubMed1995

Murine fibroblasts synthesize and secrete kininogen in response to cyclic-AMP, prostaglandin E2 and tumor necrosis factor.

Fibroblasts prepared from the meninges of newborn mice or from mouse embryos, as well as fibroblast L929 cells, secreted an immunoreactive material (ir-kininogen) against rabbit anti-mouse low-molecular-weight kininogen antibody in response to dibutyryl cAMP. Western blots using a bradykinin-directed monoclonal, as well as a polyclonal anti-mouse low-molecular-weight kininogen antibody, showed that ir-kininogen had a molecular weight of 80,000 and that it contained a kinin moiety. N-terminal amino acid sequence of the ir-kininogen was consistent with that of mouse L-kininogen. The ir-kininogen produced by fibroblasts released a kinin by incubating with trypsin and mouse submandibular gland kallikrein, and it was identified as bradykinin by means of high-performance liquid chromatography, indicating that mouse fibroblasts produce and secrete a kininogen. Forskolin, prostaglandin E2 and tumor necrosis factor alpha stimulated the production of ir-kininogen by meningeal fibroblasts, whereas neither dibutyryl cAMP nor these agents influenced kininogen production by mouse hepatocytes in primary cultures. These results demonstrated that fibroblasts are a source of kininogen in the mouse, and that it is regulated by the inflammatory mediators, prostaglandin E2 and tumor necrosis factor. Therefore locally produced kininogen is implicated in pathogenesis of inflammation.

Amino Acid Sequence↗
PubMed1987

Molecular biology of the angiotensinogen and kininogen genes.

In order to investigate the structures and expressions of the angiotensinogen and kininogen genes, we have isolated cDNA and genomic clones and characterized their structures. The following results were obtained. (a) The primary structures of rat and human angiotensinogens and bovine, human, and rat kininogens were determined, and they exhibit characteristic features. (b) Angiotensinogen and alpha 1-antitrypsin are related in not only protein structures but also gene organizations. (c) Angiotensinogen mRNA is synthesized not only in the liver but also in the brain, kidney, lung, adrenal gland, and ovary. (d) Angiotensinogen mRNA markedly increased in the liver but not in the brain after induction of acute inflammation. (e) Low molecular weight (LMW) and high molecular weight (HMW) kininogen mRNAs are generated from a single gene by alternative RNA processing events. (f) At least four types of kininogen mRNAs exist in rat liver. Two of them are LMW and HMW kininogen mRNAs, while the other two encode additional forms of kininogens (T-kininogens). (g) Two T-kininogen mRNAs but not LMW and HMW kininogen mRNAs dramatically increased after induction of acute inflammation, and T-kininogen turned out to be identical to alpha 1-major acute phase protein. (h) Kininogens have multifunctional domains; an amino-terminal domain for cystein proteinase inhibitor, a bradykinin moiety, and in the case of HMW kininogen a carboxyl-terminal domain for a cofactor of blood coagulation.

Angiotensinogen↗
PubMedDate not supplied

[Amino acid makeup, structural characteristics and substrate specificity of rabbit plasma kininogen].

Highly purified kininogen preparation with the activity of 16-18 int. units per mg was isolated from rabbit blood serum. Its molecular weight was estimated to be 54 000 by gel filtration through Sephadex G-200. Leucine was identified as N-terminal amino acid by the dansylation method. Rabbit kininogen consists of 394 amino acid residues (except tryptophane). Amino acid composition of kininogen is characterized by a high content of dicarbonic amino acids, proline and by a low content of methionine. Kininogen molecule does not contain SH-groups. 13.1-13.5 SH-groups were found in kininogen after the reduction of S-S bonds with beta-mercaptoethanol in the presence of 8 M urea, thus indicating the presence of 6-7 S-S bonds in kininogen molecule. Kininogen group does not occupy C-terminal position in the molecule, because the treatment of the protein with carboxypeptidase B does not change the content of bradykinine in it. Purified kininogen preparation is a substrate for kallikrein from rabbit blood plasma, human saliva and trypsin. Unlike trypsin, kallikreines from human blood plasma and saliva release kinines from kininogen with reduced S-S bonds. Under spontaneous reoxidation of reduced S-S bonds up to 90%, substate properties of kininogen for tripsin recover only by 50%. Rabbit kininogen is similar to beef kininogen II in its molecular weight, amino acid composition and the number of S-S bonds.

Amino Acid Sequence↗
PubMed1975

Purification and heterogeneity of human kininogen. Use of DEAE-chromatography, molecular sieving and antibody specific immunosorbents.

Various methods of preparing human kininogen were investigated with an aim to limit the immunoreactive contaminant proteins to permit purification by immunosorption. A five-step procedure is described giving 7.5% yield of highly purified kininogen (pharmacological purity 14--20) from pooled human plasma, and containing approximately 30% alpha-2HS-glycoprotein and 2.8% albumin. Alpha-2HS could not be removed by polyacrylamide gel electrophoresis or isoelectric focusing in column. Analysis of heterogeneity of kininogen after chromatography on DEAE-Sephadex using various linear gradients and gel filtration on Sephadex G-100 suggested that a minor component may be an aggregate, not included in the yield. It remains uncertain whether this component derives from an occasionally observed high molecular form of active kininogen in the primary purification steps in the 7-12 S sieve fractions from Sephadex G-200, and excluded from further purification by pooling. Purification with immunosorbents was investigated using batch operations with antibody specific polymers prepared with antisera insolubilized with ethylchloroformate. It was found that the adsorption-desorption procedure was favourable for immunization purposes in producing highly specific immunologically pure kininogen. The kininogen obtained by this method or by the removal of contaminant alpha-2HS and albumin with the corresponding antibody specific polymers gave similar heterogenous patterns by polyacrylamide gel electrophoresis, indicating a main band of kininogen and several faintly stained bands which responded only to anti-kininogen. With 200 mug of the kininogen protein purified by immunosorption using monospecific antiserum the kininogen precipitation titre was 1:8 after 6--8 weeks in rabbits. With a polymer prepared with 4 ml anti-kininogen serum (1:8) and incubated with 800 mug highly purified kininogen approximately half the protein was desorbed with 2 M and 3 M sodium iodide in the first adsorption-desorption procedure.

Amino Acids↗
PubMed1988

High-molecular weight kininogen is present in cultured human endothelial cells: localization, isolation, and characterization.

The presence of high-molecular weight (mol wt) kininogen was demonstrated in cultured human endothelial cells derived from the umbilical cord by immunofluorescence techniques. Cultured human endothelial cells contain 58 +/- 11 ng (n = 16) high-mol wt kininogen/10(6) cells as determined by an enzyme-linked immunosorbent assay (ELISA) specific for high-mol wt kininogen. High-mol wt kininogen was isolated from cultured human endothelial cells by immunoaffinity chromatography. Nonreduced sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) demonstrated that endothelial cell high-mol wt kininogen consisted of five protein bands with mol wts of 95,000, 85,000, 65,000, 46,000, and 30,000 daltons. Immunoblotting of the endothelial cell high-mol wt kininogen by using specific antisera against the heavy and light chain indicated that the 95,000-, 85,000-, and 65,000-dalton bands consisted of the heavy and light chain whereas the 46,000- and 30,000-dalton bands reacted only with the anti-light chain antiserum. Immunoprecipitation studies performed with lysed, metabolically labeled endothelial cells and monospecific antisera directed against high-mol wt kininogen suggested that high-mol wt kininogen is not synthesized by the endothelial cells. Endothelial cells cultured in high-mol wt kininogen-free medium did not contain high-mol wt kininogen. These studies indicate that endothelial cell high-mol wt kininogen was proteolytically cleaved in the culture medium and subsequently internalized by the endothelial cells. Binding and internalization studies performed with 125I-labeled, proteolytically cleaved, high-mol wt kininogen showed that endothelial cells can indeed bind and internalize proteolytically cleaved high-mol wt kininogen in a specific and saturable way.

Cells, Cultured↗
PubMed1985

Rat plasma high-molecular-weight kininogen. A simple method for purification and its characterization.

High-molecular-weight kininogen has been isolated from rat plasma in three steps in a relatively high yield. The purified preparation gave a single band on sodium dodecyl sulfate-polyacrylamide gel electrophoresis in the absence and presence of 2-mercaptoethanol, and the apparent Mr was estimated as 100,000. On incubation with rat plasma kallikrein, rat high Mr kininogen yielded a kinin-free protein consisting of a heavy chain (Mr = 64,000) and a light chain (Mr = 46,000), liberating bradykinin. The kinin-free protein was S-alkylated, and its heavy and light chains were separated by a zinc-chelating Sepharose 6B column. The amino acid compositions of rat high Mr kininogen and its heavy and light chains were very similar to those of bovine high Mr kininogen and its heavy and fragment 1.2-light chains, respectively. A high histidine content in the light chain of rat high Mr kininogen indicated the presence of a histidine-rich region in this protein as in bovine high Mr kininogen, although this region was not cleaved by rat plasma kallikrein. Rat high Mr kininogen corrected to normal values the prolonged activated partial thromboplastin time of Brown-Norway Katholiek rat plasma known to be deficient in high Mr kininogen and of Fitzgerald trait plasma. The kinin-free protein had the same correcting activity as intact high Mr kininogen. Rat high Mr kininogen also accelerated approximately 10-fold the surface-dependent activation of rat factor XII and prekallikrein, which was mediated with kaolin, amylose sulfate, and sulfatide. These results indicate that rat high Mr kininogen is quite similar to human and bovine high Mr kininogens in terms of biochemical and functional properties.

Animals↗
PubMed2003

Porcine endometrial expression of kininogen, factor XII, and plasma kallikrein in cyclic and pregnant gilts.

Establishment of pregnancy in the pig is accompanied by a localized uterine acute inflammatory response and increase in uterine blood flow. Following rapid trophoblast elongation on Day 12 of pregnancy there is an increase in tissue kallikrein activity and release of bradykinin into the uterine lumen, suggesting the kallikrein-kininogen-kinin system is active in the porcine uterus. The present study investigated endometrial expression and presence of the various factors of the kallikrein-kininogen-kinin system. Endometrial L- and H-kininogen gene expression as well as presence of kininogens in the uterine flushings was evaluated throughout the estrous cycle and early pregnancy in the pig. The possible involvement of plasma kallikrein and Factor XII, activators of the kallikrein-kininogen-kinin system, were evaluated through analysis of gene expression in endometrial and conceptus tissues. Gene expression for plasma kallikrein, Factor XII, and H-kininogen were detected in endometrium but not early conceptus tissues. Factor XII and H-kininogen gene expression were similar across the days of the estrous cycle and early pregnancy. Endometrial plasma kallikrein gene expression was low but increased on Day 15 of the estrous cycle, whereas expression was similar across the days of early pregnancy. In comparison to cyclic gilts, endometrial L-kininogen gene expression increased fourfold on Days 15 and 18 of pregnancy. Both L- and H-kininogen were detected in the uterine flushings of cyclic and pregnant gilts. Presence of L- and H-kininogen in the porcine uterus and endometrial gene expression of plasma kallikrein and Factor XII provide evidence that the kallikrein-kininogen-kinin system is biologically active during establishment of pregnancy in the pig.

Animals↗
PubMed1992

Kininogen deficiency in the rat.

The Brown Norway Katholiek (B/N-Ka) strain rat is the only animal strain that demonstrates deficiency in plasma HMW- and LMW-kininogens with a low level of prekallikrein. We developed an RIA for rat HMW-kininogen, LMW-kininogen, and T-kininogen, and using them measured these proteins in B/N-Ka and normal strain (B/N-Ki) rats. Plasma level of immunoreactive as well as kinin-releasing HMW-kininogen and LMW-kininogen in B/N-Ka rats was either around 3% of their levels in the normal B/N-Ki rats. The cause of the plasma deficiency of kininogens in the B/N-Ka strain was examined by 35S-methionine uptake of primary cultures of hepatocytes from the B/N-Ki and B/N-Ka strains. The results indicated that the kininogens were synthesized in the B/N-Ka liver but not secreted into the medium. Northern blot analysis of poly A(+)RNA extracted from the livers of both strains demonstrated that the band corresponding to mRNA of HMW-kininogen was present in the mRNA from B/N-Ka liver as well as in that from the B/N-Ki one. The band was similar in size and intensity in both cases. This result confirmed the data that immunoreactive HMW-kininogen was found in the liver of B/N-Ka rats (12). Thus, the cause of plasma deficiency of HMW-kininogen in the mutant appears to be secretory defect in nature. The B/N-Ka rats showed less reactivity to the inflammatory stimulus, such as carrageenin or kaolin, but the strain expressed almost the same response as normal rats to phorbol ester (PMA) or zymosan for pleurisy induction. These results indicate that kinin may play an important role in exudation in carrageenin- and kaolin-induced edema but not in that induced by PMA or zymosan. The deficient rat strain could be useful for differentiation of the inflammatory model which shows involvement of the kinin system.

Animals↗
PubMed1992

Distribution of immunoreactive T-kininogen in rat nervous tissues.

The distribution in the nervous system of T-kininogen, the third kallikrein-resistant kininogen of the rat, was determined using bioassays and a radioimmunoassay system. In rat brain homogenates, trypsin released large amounts of a kinin-like myostimulating activity while urinary kallikrein released small amounts. The kinins released by trypsin were identified by HPLC as mostly T-kinin. Radioimmunoassays showed that a T-kininogen-like immunoreactive factor was uniformly distributed throughout the central nervous system. Higher levels were found in female rats than in male rats. Maximum levels were observed in newborn animals. A slight increase of T-kininogen content of the brain was observed after turpentine injection while T-kininogen level in liver was dramatically increased. T-kininogen plasma contamination to the nervous tissues was estimated by injecting 125I-labelled T-kininogen. The T-kininogen content of rat cultured cells and neurons was also examined. Highest levels were found in dorsal root ganglia neurons, lower levels in Schwann cells, phaeochromocytoma cells, mixed cells from spinal ganglion and in astrocytes. Immunocytochemistry showed the presence of T-kininogen in the cytoplasm of cultured dorsal root ganglia neurons and embryonic hippocampal neurons. The distribution of T-kininogen throughout the central and peripheral nervous system of the rat, the variations of its level during the life span suggest that T-kininogen would play the role of a cysteine proteinase inhibitor and not that of a T-kinin-releasing substrate in nervous tissues.

Aging↗
PubMed1989

Sex dimorphism and inflammatory regulation of T-kininogen and T-kininogenase.

Studies were carried out in order to better understand hormonal and inflammatory regulation of the T-kininogen and T-kininogenase system. T-kininogen from rat serum and T-kininogenase from rat submandibular gland were purified to homogeneity, and specific antisera to the purified proteins were generated. Simple, sensitive and specific radioimmunoassays were developed for measuring both T-kininogen and T-kininogenase. The assays incorporated a modified poly(ethylene glycol) technique for separating free from antibody-bound forms. Optimal combinations of poly(ethylene glycol) and gamma-globulin were found, yielding low background and high specific binding. The assays can detect a minimum of 160 pg of T-kininogen and 80 pg of T-kininogenase per tube. Serial dilutions of sera from normal and turpentine-treated rats showed complete parallelism with the T-kininogen standard curve. T-kininogen levels in rat serum and rat tissues increased more than 10-fold following turpentine treatment, while T-kininogenase levels in the submandibular gland and other tissues remained unchanged. Through use of a kinin-directed kininogen monoclonal antibody, Western blots of two-dimensional gels of serum following acute inflammation showed increased levels of several kininogens which vary in both molecular weight and isoelectric point. Analysis of serum kininogen levels shows sexual dimorphism, with female rats having 3.9-fold higher levels than males. Contrarily, T-kininogenase levels in the submandibular gland of male rats are 2.4-fold higher than those in females. The studies also showed that the T-kininogen and T-kininogenase system is regulated by sex hormones. T-kininogen is an acute-phase protein whose rapid increase and mobilization following inflammation may provide a primary defense against proteolytic damage during trauma.

Animals↗
PubMed1995

Human kininogens interact with M protein, a bacterial surface protein and virulence determinant.

Streptococcus pyogenes, the most significant streptococcal species in clinical medicine, expresses surface proteins with affinity for several human plasma proteins. Here we report that kininogens, the precursors to the vasoactive kinins, bind to the surface of S. pyogenes. M protein, a surface molecule and a major virulence factor-in these bacteria, occurs in > 80 different serotypes. Among 49 strains of S. pyogenes, all of different M serotypes, 41 bound radiolabelled kininogens, whereas 6 M protein-negative mutant strains showed no affinity. M protein of most serotypes bind fibrinogen, and among the 55 strains tested, binding of kininogens was closely correlated to fibrinogen binding (r = 0.88, P < 0.0001). Western blotting, slot binding and enzyme immunoassay experiments demonstrated that M proteins isolated from S. pyogenes of three different M protein serotypes (M1, M6 and M46) bound kininogens. The affinity between kininogens and M1 protein was determined to be 5 x 10(7) M-1 and < or = 10(6) M-1 for high molecular weight (H-kininogen) and low molecular weight kininogen, respectively. The kininogen binding site was tentatively mapped to the N-terminal portion of M1 protein, and this site does not overlap the specific and separate binding sites for albumin, IgG and fibrinogen using monoclonal antibodies to, and synthetic peptides of, the kininogen sequence, the major M protein-binding site(s) was mapped to the C-terminal portion of the H-kininogen light chain. We anticipate that the kininogen-M protein interaction contributes to the host-parasite relationship in S. pyogenes infections.

Amino Acid Sequence↗
PubMed1999

Mapping of the discontinuous H-kininogen binding site of plasma prekallikrein. Evidence for a critical role of apple domain-2.

Plasma prekallikrein, a zymogen of the contact phase system, circulates in plasma as heterodimeric complex with H-kininogen. The binding is mediated by the prekallikrein heavy chain consisting of four apple domains, A1 to A4, to which H-kininogen binds with high specificity and affinity (K(D) = 1.2 x 10(-8) M). Previous work had demonstrated that a discontinuous kininogen-binding site is formed by a proximal part located in A1, a distal part exposed by A4, and other yet unidentified portion(s) of the kallikrein heavy chain. To detect relevant binding segment(s) we recombinantly expressed single apple domains and found a rank order of binding affinity for kininogen of A2 > A4 approximately A1 > A3. Removal of single apple domains in prekallikrein deletion mutants reduced kininogen binding by 21 (A1), 64 (A2), and 24% (A4), respectively, whereas deletion of A3 was without effect. Transposition of homologous A2 domain from prekallikrein to factor XI conferred high-affinity kininogen binding from the former to the latter. The principal role of A2 for H-kininogen docking to the prekallikrein heavy chain was further substantiated by the finding that cleavage of a single peptide bond in A2 drastically diminished the H-kininogen binding affinity. Furthermore, the epitope of monoclonal antibody PKH6 which blocks kallikrein-kininogen complex formation with an IC(50) of 8 nM mapped to the center portion of domain A2. Our data indicate that domain A2 and two flanking sequence segments of A1 and A4 form a discontinuous binding platform for H-kininogen on the prekallikrein heavy chain. Domain-specific antibodies directed to these critical sites efficiently interfered with contact phase-induced bradykinin release from H-kininogen.

Binding Sites↗
PubMed1986

Completion of the primary structure of human high-molecular-mass kininogen. The amino acid sequence of the entire heavy chain and evidence for its evolution by gene triplication.

The amino acid sequence of the heavy chain of human high-molecular-mass kininogen has been determined. It completes the primary structure of the high-Mr kininogen molecule. The heavy chain contains 362, the total kininogen molecule 626 amino acid residues. Three carbohydrate side chains were found in the heavy chain, all of them N-glycosidically linked to asparagine, which is present in the acceptor sequon Asn-Xaa-Thr (or -Ser); one additional potential glycosylation site devoid of a sugar side chain is found at position 30. There is a high degree of homology between the heavy chains of human high-Mr kininogen and bovine high-Mr kininogen (74% identity), or rat T-kininogen (61%). Comparison of the primary structure of human high-Mr kininogen with that of human low-Mr kininogen predicted from its cDNA sequence, reveals that the heavy chains of the two human kininogens are completely identical. Two heavy chain segments believed to contain the reactive sites for cysteine proteinase inhibition show an extensive sequence homology with other mammalian cysteine proteinase inhibitors. Within the heavy chain of human high-Mr kininogen are repetitive units strongly suggesting that the heavy chain of human kininogens has evolved from at least two ancestral units by a series of gene duplication and fusion events.

Amino Acid Sequence↗
PubMed1987

Determination of the bifunctional properties of high molecular weight kininogen by studies with monoclonal antibodies directed to each of its chains.

In normal human plasma two forms of kininogen exist, low molecular weight kininogen (LMWK) and high molecular weight kininogen (HMWK). When these proteins are cleaved they are found to have a common heavy chain and bradykinin, but each has a unique light chain. Monoclonal antibodies to the heavy and light chains of HMWK have been developed, and the effects of each on the function of this protein are defined. Initial studies showed that an antibody, C11C1, completely neutralized the coagulant activity of plasma HMWK whereas another antibody, 2B5, did not. On a competitive enzyme-linked immunosorbent assay (CELISA) the C11C1 antibody was consumed by kininogen antigen in normal plasma but not by kininogen antigen in HMWK-deficient plasma. On immunoblot, the C11C1 antibody recognized one kininogen protein in normal plasma and did not recognize any kininogen antigen in HMWK-deficient plasma. These combined studies indicated that the C11C1 antibody was directed to an epitope on the unique 46-kDa light chain of HMWK. In contrast, the 2B5 antibody on a CELISA was consumed by kininogen antigen in both normal plasma and HMWK-deficient plasma but not by total kininogen-deficient plasma. On immunoblot, the 2B5 antibody recognized both kininogens in normal plasma but only LMWK in HMWK-deficient plasma. These combined studies indicated that the 2B5 antibody was directed to the common 64-kDa heavy chain of the plasma kininogens. Utilizing direct binding studies or competition kinetic experiments, the 2B5 and C11C1 antibodies bound with high affinity (1.71 and 0.77 nM, respectively) to their antigenic determinants on the HMWK molecule. The 2B5 antibody did neutralize the ability of HMWK to inhibit platelet calpain. These studies with monoclonal antibodies directed to each of the HMWK chains indicate that HMWK is a bifunctional molecule that can serve as a cofactor for serine zymogen activation and an inhibitor of cysteine proteases.

Animals↗
PubMed1980

Immunochemical studies of human high molecular weight kininogen and of its complexes with plasma prekallikrein or kallikrein.

Human plasm contains at least two distinct kininogens, designated high Mr and low Mr kininogens, that differ in their Mr and susceptibility to different kallikreins. By limited proteolysis, plasma kallikrein cleaves high Mr kininogen to liberate kinin and gives a molecule containing two disulfide-linked polypeptide chains. Following reduction and alkylation of the two-chain molecule, the heavy chain and the light chain were isolated, and antisera were raised in goats against the alkylated heavy and light chains. The anti-heavy chain antiserum immunoprecipitated both high Mr and low Mr kininogen, whereas the anti-light chain antiserum was specific for high Mr kininogen. Thus, the heavy chain of kinin-free high Mr kininogen and low Mr kininogen extensively share identical immunologic determinants. In contrast, the immunologic determinants of the isolated light chain are unique to high Mr kininogen. Using immunochemical techniques, it was shown that high Mr kininogen or the light chain derived from it forms a complex either with prekallikrein or with kallikrein. Titrations of prekallikrein or kallikrein with increasing amounts of either high Mr kininogen or its alkylated light chain indicated that the complexes contain equimolar amounts of each molecule. These results show that a single site for prekallikrein or kallikrein binding to high Mr kininogen resides in the light chain region of the molecule.

Epitopes↗
PubMed1996

Phosphatidylethanolamine induces specific conformational changes in the kininogens recognizable by antiphosphatidylethanolamine antibodies.

Autoantibodies to the zwitterionic phospholipid (PL), phosphatidylethanolamine (PE) have been described in patients with thrombotic diseases. Recently, we reported that many antiphosphatidylethanolamine antibodies (aPE) are not specific for PE per se, but are directed to plasma proteins which can bind PE, for example, high molecular weight kininogen (HK), low molecular weight kininogen (LK) and/or proteins in complex with HK, factor XI or prekallikrein. In the ELISA, we now show that intact HK binds to all PL tested. By using a monoclonal antibody (mAb) to the HK light chain, binding to cardiolipin (CL) was highest followed by phosphatidylserine (PS), PE and phosphatidylcholine (PC). By contrast, LK bound best to PE, with lesser amounts binding to PC and CL. Many aPE recognize only a kininogen-PE complex and neither PE nor kininogen when they are tested independently. We now report that these aPE are specific for the kininogen-PE complex as they do not recognize the kininogens when the latter are presented on other PL substrates. This indicates that PE induces unique antigenic conformational changes in the kininogens which are not induced when the kininogens bind to other PL. The kininogens bind to platelets and endothelial cells through an as yet undefined receptor. Since PE is a normal constituent of the outer layer of cell and platelet plasma membranes, it is available for the kininogens to bind. In vitro studies showed that purified IgG which bound kininogen-PE complexes in ELISA also caused platelets to undergo irreversible aggregation when stimulated by subthreshold concentrations of bovine thrombin.

Animals↗