Direct evidence for multifacial contacts between high molecular weight kininogen and plasma prekallikrein

Plasma Kallikrein Inhibitors in Cardiovascular Disease: An Innovative Therapeutic Approach

Plasma prekallikrein is the liver-derived precursor of the trypsin-like serine protease plasma kallikrein, and circulates in plasma bound to high molecular weight kininogen. Plasma prekallikrein is activated to plasma kallikrein by activated factor XII or prolylcarboxypeptidase. Plasma kallikrein regulates the activity of multiple proteolytic cascades in the cardiovascular system such as the intrinsic pathway of coagulation, the kallikrein-kinin system, the fibrinolytic system, the renin-angiotensin system, and the complement pathways. As such, plasma kallikrein plays a central role in the pathogenesis of thrombosis, inflammation, and blood pressure regulation. Under physiological conditions, plasma kallikrein serves as a cardioprotective enzyme. However, its increased plasma concentration or hyperactivity perpetuates cardiovascular disease (CVD). In this article, we review the biochemistry and cell biology of plasma kallikrein and summarize data from preclinical and clinical studies that have established important functions of this serine protease in CVD states. Finally, we propose plasma kallikrein inhibitors as a novel class of drugs with potential therapeutic applications in the treatment of CVDs.

[An elderly case of congenital prekallikrein deficiency]

The proband is a 69-year-old woman with purpura and subcutaneous hematoma.We investigated this patient with prekallikrein (PK) deficiency, using both standard coagulation study and molecular genetic analysis of the PK gene. In a coagulation study, the prothrombin time (PT) was normal but the activated partial thromboplastin time (APTT) was prolonged. Preincubation of normal plasma with APTT reagent caused shortening of abnormal clotting time. Plasma PK activity was <1%. Her parents were cousins. Molecular genetic analysis showed a homozygous Gly401Glu substitution in exon 11 in the PK gene. This mutation has already been reported in a Japanese patient as PK Tokushima. Gly401 is positioned in PK light chain, which encodes the serine protease domain. The disulfide binding is formed between Cys400 and Cys416, thus Gly401 is located next to His415, which is one of the activation peptides and is important in supporting the correct conformation of proteins. Therefore, we suggest that this mutation may prevent formation of disulfide binding and reduce enzyme activity. In conclusion, in the elderly case with prolonged APTT, we should consider the contact factor deficiency and determine PK activity apart from the abnormality of coagulation factor VIII, IX, XI and XII activities.

A new type of plasma prekallikrein deficiency associated with homozygosity for Gly104Arg and Asn124Ser in apple domain 2 of the heavy-chain region

Three Japanese patients demonstrated plasma prekallikrein (PK) deficiency (PKD) after an examination of the proband family line named 'PKD Seki'. A molecular genetic analysis of these PK genes showed homozygous amino acid substitutions Gly104Arg and Asn124Ser in exon 5, which encodes part of the apple domain 2 (A2) of the heavy chain. This is the first case involving substitutions in the heavy chain of the PK gene which affected blood coagulation. Because the apple domains of PK bind to the C-terminal domain (D6(H)) of high-molecular weight kininogen (HMWK), the two substitutions in A2 may therefore be the main cause of PKD Seki. We subsequently investigated the effects of amino acid substitutions in A2 to elucidate the binding activity of PK to HMWK using mutant A2 proteins produced in Escherichia coli. We clearly demonstrated that the Gly104Arg-substitution with the Asn124Ser-substitution in A2 reduce the binding activity of A2 to HMWK. PKD Seki is the first significant case to show the amino acid substitutions in the A2 affecting the binding capacity of PK with HMWK. Our findings therefore suggest that the binding of PK to HMWK may play a crucial role in the first step of blood coagulation.

The kallikrein-kininogen-kinin system: lessons from the quantification of endogenous kinins

The purpose of the present review is to describe the place of endogenous kinins, mainly bradykinin (BK) and des-Arg(9)-BK in the kallikrein-kininogen-kinin system, to review and compare the different analytical methods reported for the assessment of endogenous kinins, to explain the difficulties and the pitfalls for their quantifications in biologic samples and finally to see how the results obtained by these methods could complement and extend the pharmacological evidence of their pathophysiological role.

Fourier transform infrared (FT-IR) spectroscopic studies of peptide models for interaction of the binding regions of high molecular weight kininogen and prekallikrein

The binding sites for high molecular weight kininogen (HK) on prekallikrein (PK) are composed of two discontinuous segments in the primary sequence, one in Apple 1 domain (PK56=F56-G86) and the other in Apple 4 (PK266=K266-G295). The site on HK, HK31, is subsumed in a 31-amino-acid sequence (S565-K595) near the C-terminus which has the same affinity for prekallikrein as the entire HK molecule. The binding among them is likely due to conformational changes which serve to juxtapose the PK binding domain within HK with the HK binding site. Resolution-enhanced Fourier transform infrared spectroscopy (FT-IR) has been employed to analyze the contents of secondary structural elements of PK56 and HK31 and to reveal the possible specific binding portion and structural changes in HK31 and PK56 upon binding. From the amide I bands of their deconvoluted FT-IR spectra, it is known that PK56 contains no helix component, while HK31 has two different helical conformations. A quantitative comparison of the spectra of HK31, PK56 and their binding complex suggests that the conformation of 3(10)-helix in HK31 has been changed to an alpha-helix, and one disordered segment of PK56 may have been changed to extended conformation. The other structural components in PK56 and HK31 remain unchanged. Since previous studies have shown that these peptides mimic the natural protein in their bioactivity, their interaction may reflect similar changes in the natural molecules.

High Molecular Weight Kininogen Peptides Inhibit the Formation of Kallikrein on Endothelial Cell Surfaces and Subsequent Urokinase-Dependent Plasmin Formation

A sequence of 31 amino acids (S565-K595) in domain 6 of the light chain of high molecular weight kininogen (HK) has previously been shown to be responsible for the binding of plasma prekallikrein (PK) or kallikrein. To find effective peptides that might block binding between HK and PK on cell surfaces, a new series of synthetic peptides has now been prepared that incorporates portions of this binding domain sequence. For mapping the minimal sequence within HK, these new peptides were tested for their ability to compete with HK for binding PK in a cell-free system and on human umbilical vein endothelial cells (HUVEC). In the former, at pH 7.4, the kds for binding between kallikrein and either D567-K595, S565-P594, D567-S593, or D567-T591 were all similar to that for the binding of S565-K595 (0.2 to 0.4 μmol/L), but those for the binding of D568-K595, W569-K595, and D567-P589 were an order of magnitude greater (kd = 2 to 5 μmol/L). D567-S586, the shortest chain length of the N- and C-terminal truncation sequences tested, does not effectively compete with kininogen for kallikrein binding (kd = 100 μmol/L). These results imply that D567-T591, a 25-residue peptide (HK25c), contains sufficient structural information for binding kallikrein in solution. D567-T591 also is the minimum structural sequence to block binding of kallikrein to HUVEC-bound HK (IC50 = 50 nmol/L) and to inhibit PK activation to kallikrein on the cell surface (IC50 = 80 nmol/L). In addition, D567-T591 also inhibits the generation of kallikrein-activated urokinase, which activates plasminogen to plasmin (IC50 = 100 nmol/L). Thus, HK-derived peptides may be useful compounds for modulating excessive fibrinolysis and hypotension in sepsis and multiple trauma.

High Molecular Weight Kininogen Peptides Inhibit the Formation of Kallikrein on Endothelial Cell Surfaces and Subsequent Urokinase-Dependent Plasmin Formation

A sequence of 31 amino acids (S565-K595) in domain 6 of the light chain of high molecular weight kininogen (HK) has previously been shown to be responsible for the binding of plasma prekallikrein (PK) or kallikrein. To find effective peptides that might block binding between HK and PK on cell surfaces, a new series of synthetic peptides has now been prepared that incorporates portions of this binding domain sequence. For mapping the minimal sequence within HK, these new peptides were tested for their ability to compete with HK for binding PK in a cell-free system and on human umbilical vein endothelial cells (HUVEC). In the former, at pH 7.4, the kds for binding between kallikrein and either D567-K595, S565-P594, D567-S593, or D567-T591 were all similar to that for the binding of S565-K595 (0.2 to 0.4 μmol/L), but those for the binding of D568-K595, W569-K595, and D567-P589 were an order of magnitude greater (kd = 2 to 5 μmol/L). D567-S586, the shortest chain length of the N- and C-terminal truncation sequences tested, does not effectively compete with kininogen for kallikrein binding (kd = 100 μmol/L). These results imply that D567-T591, a 25-residue peptide (HK25c), contains sufficient structural information for binding kallikrein in solution. D567-T591 also is the minimum structural sequence to block binding of kallikrein to HUVEC-bound HK (IC50 = 50 nmol/L) and to inhibit PK activation to kallikrein on the cell surface (IC50 = 80 nmol/L). In addition, D567-T591 also inhibits the generation of kallikrein-activated urokinase, which activates plasminogen to plasmin (IC50 = 100 nmol/L). Thus, HK-derived peptides may be useful compounds for modulating excessive fibrinolysis and hypotension in sepsis and multiple trauma.

Physical and biological significance of peptide sequences mediating the interaction between high molecular weight kininogen and plasma prekallikrein

HK31 (S565-K595) has previously been shown to encompass the binding domain for plasma prekallikrein (PK) within domain 6 of high molecular weight kininogen (HK). The complementary binding domain for HK within PK is mapped to PK56 (F56-G86), in the Apple 1 domain and to PK266 (K266-C295) in the Apple 4 domain. Isothermal titration calorimetry demonstrated that either PK peptide binds to HK31 in 1:1 stoichiometry. Binding of the alternate PK peptide into a ternary complex is facilitated nearly 2-fold. Fluorescence emission spectroscopy revealed that only the binding of PK56 caused a limited decrease in intrinsic tryptophane fluorescence emission intensity of HK31. We conclude that the two PK peptides bind to the HK peptide at different sites. To map the minimal sequence within HK31, truncated new peptides were tested for their ability to compete with HK for binding PK in a cell-free system. D567-T591, a 25-residue peptide which contains sufficient structural information for binding kallikrein in solution, blocked the binding of kallikrein to HK bound to endothelial cells and inhibited PK activation to kallikrein and the generation of kallikrein-activated urokinase on endothelial cell surfaces. HK-derived peptides could modulate excessive fibrinolysis and hypotension in sepsis and multiple trauma.