A comparison of the kallikrein-kinin system in sheep and dogs

Three preparations of kallikrein, made from the urine of man, dog and sheep, all formed active kinins when incubated with the plasma of sheep or dogs. The six kinins could not be distinguished from one another by parallel assays on guinea-pig ileum, rat uterus and rat duodenum; they are thought to be identical, or nearly so. As judged by the amount of kinin produced, a sample of dog plasma appeared to contain about 4.3 times as much substrate as a sample of sheep plasma. This ratio did not depend on the kallikrein used. Attempts to compare the three kallikreins gave inconsistent results which may be due to presence in the preparations of kallikrein of other enzymes acting on the same substrate. Sheep plasma does not form kinins on contact with glass.

Purification and partial characterization of kininogenase activity from Schistosoma mansoni adult worms

An enzyme presenting kallikrein-like activity (designated sK1) was purified from the supernatant of Schistosoma mansoni adult worm homogenate. The enzyme cleaves bradykinin from purified rat plasma kininogen. Activity was optimal at pH 9.0 and the enzyme showed amidolytic activity, since it hydrolysed the kallikrein synthetic substrate D-Pro-Phe-Arg-p-nitroanilide. The activity of sK1 upon rat plasma kininogen was strongly inhibited by the serine proteinase inhibitors phenylmethanesulfonyl fluoride, aprotinin or soybean trypsin inhibitor, but not by ethylenediaminetetraacetic acid or sodium tetrathionate. The molecular mass of sK1, as determined by polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulfate, was 66 kDa and the pI value, estimated by analytical chromatofocusing, was 4.2. Physical and chemical properties suggest that sK1 is a serine proteinase of the kallikrein family. Evidence is presented which suggests that sK1 is a component of the tegumental surface of the parasite and the levels of its activity in the male adult worm are approximately 21 times higher than those in the female adult worm. The intravenous injection of 3 micrograms of sK1 into an anaesthetized rat induced a drastic reduction in the arterial blood pressure of the animal. This effect lasted for about 1 min, and was followed by a progressive recovery of the arterial pressure. Neither bradycardia nor cardiac arrhythmias were noticed, suggesting a peripheral vasodilation effect. The presence of sK1 on the surface of adult male worms could play an important role in the wandering capacity of coupled worms into the visceral vasculature of the host.

Expression and characterization of human tissue kallikrein variants

Human tissue kallikrein is a serine protease implicated in the pathology of various inflammatory disorders. As one of the two principal enzymes that generate proinflammatory kinin peptides in vivo, tissue kallikrein represents an attractive target for therapeutic intervention in diseases such as asthma, pancreatitis, and rheumatoid arthritis. Three distinct human tissue kallikrein variants, differing in one or two amino acid substitutions, are predicted to exist based on genomic or cDNA nucleotide sequences derived from different tissues. The effects of these substitutions on the biochemical properties of tissue kallikrein are unknown but could, in principle, confer tissue-specific functions on the enzyme or affect the clinical utility of specific kallikrein inhibitors. All three variants, as well as a deglycosylated derivative, were expressed in high yield as recombinant proteins in Pichia pastoris. The recombinant kallikrein variants and natural urinary kallikrein all hydrolyzed synthetic peptides with similar specificity and efficiency and released kallidin from kininogen at comparable rates. Similarly, no significant differences were observed in the interactions between kallikrein variants and protein inhibitors such as SBTI, alpha1-PI, and aprotinin. We conclude that the known tissue kallikrein variants represent allelic variants and are not likely to have tissue-specific activity related to the amino acid substitutions.

Crystal structure of recombinant human tissue kallikrein at 2.0 A resolution

Human tissue kallikrein, a trypsin-like serine protease involved in blood pressure regulation and inflammation processes, was expressed in a deglycosylated form at high levels in Pichia pastoris, purified, and crystallized. The crystal structure at 2.0 A resolution is described and compared with that of porcine kallikrein and of other trypsin-like proteases. The active and S1 sites (nomenclature of Schechter I, Berger A, 1967, Biochem Biophys Res Commun 27:157-162) are similar to those of porcine kallikrein. Compared to trypsin, the S1 site is enlarged owing to the insertion of an additional residue, cis-Pro 219. The replacement Tyr 228 --> Ala further enlarges the S1 pocket. However, the replacement of Gly 226 in trypsin with Ser in human tissue kallikrein restricts accessibility of substrates and inhibitors to Asp 189 at the base of the S1 pocket; there is a hydrogen bond between O delta1Asp189 and O gammaSer226. These changes in the architecture of the S1 site perturb the binding of inhibitors or substrates from the modes determined or inferred for trypsin. The crystal structure gives insight into the structural differences responsible for changes in specificity in human tissue kallikrein compared with other trypsin-like proteases, and into the structural basis for the unusual specificity of human tissue kallikrein in cleaving both an Arg-Ser and a Met-Lys peptide bond in its natural protein substrate, kininogen. A Zn+2-dependent, small-molecule competitive inhibitor of kallikrein (Ki = 3.3 microM) has been identified and the bound structure modeled to guide drug design.

Determination and analysis of antigenic epitopes of prostate specific antigen (PSA) and human glandular kallikrein 2 (hK2) using synthetic peptides and computer modeling

Prostate specific antigen (PSA) and human glandular kallikrein 2 (hK2), produced essentially by the prostate gland, are 237-amino acid monomeric proteins, with 79% identity in primary structure. Twenty-five anti-PSA monoclonal antibodies (Mabs) were studied for binding to a large array of synthetic linear peptides selected from computer models of PSA and hK2, as well as to biotinylated peptides covering the entire PSA sequence. Sixteen of the Mabs were bound to linear peptides forming four independent binding regions (I-IV). Binding region I was localized to amino acid residues 1-13 (identical sequence for PSA and hK2), II (a and b) was localized to residues 53-64, III (a and b) was localized to residues 80-91 (= kallikrein loop), and IV was localized to residues 151-164. Mabs binding to regions I and IIa were reactive with free PSA, PSA-ACT complex, and with hK2; Mabs binding to regions IIb, IIIa, and IV were reactive with free PSA and PSA-ACT complex, but unreactive with hK2; Mabs binding to region IIIb detected free PSA only. All Mabs tested (n = 7) specific for free PSA reacted with kallikrein loop (binding region IIIb). The presence of Mabs interacting with binding region I did not inhibit the catalytic activity of PSA, whereas Mabs interacting with other binding regions inhibited the catalysis. Theoretical model structures of PSA, hK2, and the PSA-ACT complex were combined with the presented data to suggest an overall orientation of PSA with regard to ACT.

Structure and other chemical characterizations of gila toxin, a lethal toxin from lizard venom

The complete primary structure of a lethal toxin, horridum toxin, from the venom of the lizard, Heloderma horridum horridum, was determined by Edman degradation. The amino acid sequence was deduced by overlapping peptide fragments generated by chemical and enzymatic digestions. Horridum toxin causes hemorrhage in internal organs and particularly in the eye, leading to exophthalmia, an effect that has not been observed for other toxins. It is a glycoprotein with a total of 210 residues. Examination of the primary sequence revealed that horridum toxin has considerable homology to tissue-type kallikrein and trypsin. Furthermore, synthetic substrates for trypsin, such as tosyl-L-arginine methyl ester, benzoyl-L-arginine ethyl ester and other p-nitroanilide substrates, were hydrolyzed. The toxin released bradykinin upon hydrolysis of kininogen. This enzymatic behavior is similar to that of plasma kallikrein: however, the presence of a characteristic "kallikrein-like" loop at 91-100 (GTIYNCNYVN) in the primary structure and other features similar to tissue kallikrein suggest that horridum toxin is more like tissue kallikrein. This toxin degraded all three chains of fibrinogen but did not form a clot, which suggests that it is different from thrombin. Moreover, it differs from another lethal factor from H. horridum horridum, gila toxin, which has 245 amino acid residues and does not cause exophthalmia.

Purification, properties, and N-terminal amino acid sequence of a kallikrein-like enzyme from the venom of Lachesis muta rhombeata (Bushmaster)

Pit viper venoms contain multiple proteinases which cause considerable damage in tissues and systemic effects after envenomation. A proteinase, kallikrein-like enzyme, belonging to the serine group must play a very important role on systemic effects. The corresponding enzyme from Lachesis muta rhombeata venom was purified to homogeneity by a combination of isoelectrofocusing fractionation followed by one step of gel filtration HPLC. The enzyme focused with pI 5.0-6.5, it had a molecular mass of 32 kDa by gel filtration HPLC, had edematogenic activity, and induced a hypotensic effect in anesthetized rats. It exhibited strong N-alpha-tosyl-L-Arg methyl esterase (955.38 units/mg) and N-Bz-DL-Arg-pNA amidolytic (233.02 units/mg) activities, hydrolyzed tripeptide nitroanilide derivatives weakly or not at all, and cleaved selectively the A-alpha and B-beta chains of fibrinogen, apparently leaving the Y-chain unaffected. The 30 N-terminal amino acid sequence of the L. m. rhombeata protein showed greatest identity (74% in 26 amino acids) with Crotalus viridis kallikrein-like protein, but significant similarities in sequence were observed with enzymes from other snake venoms and pig pancreatic kallikrein.

Inclusion of conserved buried water molecules in the model structure of rat submaxillary kallikrein

A new approach to the molecular modelling of homologous serine proteases is adopted, by including a set of 21 buried waters known to be preserved in enzymes sharing the primary specificity of trypsin, in the homology modelling of rat submaxillary gland kallikrein. Buried waters--water molecules sequestered from bulk solvent within a protein matrix--appear to be integral conserved components of all serine proteases of known structure and should be incorporated into serine protease models built on the basis of sequence/structural homology to this family. The absence of such waters might induce errors in a force field simulation, favouring the formation of nonexistent hydrogen bonds and locally inaccurate structure. The kallikrein model refinement has led to the conclusion that an additional buried water should be added to the original rigid matrix of 21 conserved water molecules. The structurally preserved protein cavities of such waters validate the modelled structure.

Structure of mouse 7S NGF: a complex of nerve growth factor with four binding proteins

BACKGROUND

Nerve growth factor (NGF) is a neurotrophic factor that promotes the differentiation and survival of certain populations of neurons in the central and peripheral nervous systems. 7S NGF is an alpha 2 beta 2 gamma 2 complex in which the beta-NGF dimer (the active neurotrophin) is associated with two alpha-NGF and two gamma-NGF subunits, which belong to the glandular kallikrein family of serine proteinases. The gamma-NGF subunit is an active serine proteinase capable of processing the precursor form of beta-NGF, whereas alpha-NGF is an inactive serine proteinase. The structure of 7S NGF could be used as a starting point to design inhibitors that prevent NGF binding to its receptors, as a potential treatment of neurodegenerative diseases.

RESULTS

The crystal structure of 7S NGF shows that the two gamma-NGF subunits make extensive interactions with each other around the twofold axis of the complex and have the C-terminal residues of the beta-NGF subunits bound within their active sites. The 'activation domain' of each of the alpha-NGF subunits is in an inactive (zymogen-like) conformation and makes extensive interactions with the beta-NGF dimer. The two zinc ions that stabilize the complex are located at the relatively small interfaces between the alpha-NGF and gamma-NGF subunits.

CONCLUSIONS

The structure of 7S NGF shows how the twofold axis of the central beta-NGF dimer organizes the symmetry of this multisubunit growth factor complex. The extensive surface of beta-NGF buried within the 7S complex explains the lack of neurotrophic activity observed for 7S NGF. The regions of the beta-NGF dimer that contact the alpha-NGF subunits overlap with those known to engage NGF receptors. Two disulphide-linked loops on alpha-NGF make multiple interactions with beta-NGF and suggest that it might be possible to design peptides that inhibit the binding of beta-NGF to its receptors.

Renal epidermal growth factor precursor: proteolytic processing in an in vitro cell-free system

The enzymatic processing of the membrane-bound renal epidermal growth factor precursor (proEGF) could be an important step in the control of nephrogenic repair consecutive to kidney insult. The enzyme machinery responsible for that processing was examined in a cell-free system consisting of renal membranes isolated from kidney homogenates by differential centrifugation, and incubated in vitro. After a 24-h incubation at 37 degrees C, 6-14% of membrane-bound proEGF was processed and soluble products with EGF immunoreactivity were released. As revealed by HPLC and Western blotting analysis, the products of proEGF proteolysis consisted of 6 kDa EGF (the molecular weight of mature EGF) and two polypeptides with molecular weights around 45 kDa. Interestingly the 45 kDa EGF forms, like the 6 kDa EGF, exhibited mitogenic activity toward growth-arrested NRK-52E renal cell line. The kinetic study of proEGF degradation gave data consistent with the 45 kDa product(s) being processing intermediate(s) between proEGF and 6 kDa EGF. The enzymatic activity responsible for proEGF nicking was inhibited by divalent heavy metal ions (Cu2+ or Zn2+) and several protease inhibitors (aprotinin, PMSF, leupeptin, soybean trypsin inhibitor), suggesting that proEGF is processed by kallikrein-like serine proteases present in the membrane preparations. Along with previous studies, the current observations suggest that renal kallikreins might play a role in renal tubular regeneration by promoting the release of soluble EGF in renal tissue.

Purification and characterization of a kinin- and angiotensin II-forming enzyme in the dog heart

OBJECTIVE

To purify and characterize a kinin-forming enzyme in the dog heart and to examine the ability of this enzyme to generate angiotensin (Ang) II from Ang I.

METHODS

The enzyme was isolated from heart homogenate using a diethylaminoethyl-Sepharose column, an aprotinin affinity column and a wheat germ lectin-Sepharose 6MB column. Kininogenase activity was assessed with a kinin radioimmunoassay after samples had been incubated with bovine low-molecular-mass kininogen at 37 degrees C for 1 h. Ang I-converting activity was assessed by the quantitation of Ang II formed by incubation of the sample with Ang I at 37 degrees C for 3 h, using high performance liquid chromatography. The enzyme was subjected to 12.5% sodium dodecyl sulphate-polyacrylamide gel electrophoresis, stained by Coomassie brilliant blue and transferred electrically to a membrane with glycoprotein staining.

RESULTS

The purified enzyme is a glycoprotein with an apparent relative molecular mass of 65 kDa by sodium dodecyl sulphate-polyacrylamide gel electrophoresis. Its kininogenase activity was approximately 20 micrograms bradykinin/h per mg protein at an optimal pH of 8.0. The enzyme also converted Ang I to Ang II at an optimal pH of 6.5. Its specific activity was approximately 2 micrograms Ang II/h per mg protein. Both activities were inhibited by aprotinin, a tissue kallikrein inhibitor. Western blot analysis using polyclonal antibody against this enzyme demonstrated that this enzyme exists both in the myocardium and in the coronary artery.

CONCLUSIONS

The present study showed that the kinin-forming enzyme in the dog heart is a kallikrein-like enzyme that is different from cathepsin D, cathepsin G and chymase. It is also able to Ang I to Ang II. This enzyme might play a role in regulating myocardial perfusion, mainly by generating kinins and in part by forming Ang II.

Tissue kallikrein-like immunoreactive material decorates neuritic plaques of Alzheimer patients

The neuroanatomical distribution of the proteinase kallikrein (EC. 3.4.21.35) in human brain was examined immunohistochemically by using antiserum against human tissue kallikrein. In normal nervous tissue only faint immunostaining of some neocortical and hippocampal neurons was observed. Glial cells were found to be immunonegative for kallikrein. In Alzheimer disease (AD) brains kallikrein-like immunoreactivity was associated, in some areas, with nerve cells and, especially in the neocortex, with numerous neuritic plaques. A possible function of the proteinase in AD-associated cascade of inflammatory response is supposed.

A new structural class of serine protease inhibitors revealed by the structure of the hirustasin-kallikrein complex

BACKGROUND

Hirustasin belongs to a class of serine protease inhibitors characterized by a well conserved pattern of cysteine residues. Unlike the closely related inhibitors, antistasin/ghilanten and guamerin, which are selective for coagulation factor Xa or neutrophil elastase, hirustasin binds specifically to tissue kallikrein. The conservation of the pattern of cysteine residues and the significant sequence homology suggest that these related inhibitors possess a similar three-dimensional structure to hirustasin.

RESULTS

The crystal structure of the complex between tissue kallikrein and hirustasin was analyzed at 2.4 resolution. Hirustasin folds into a brick-like structure that is dominated by five disulfide bridges and is sparse in secondary structural elements. The cysteine residues are connected in an abab cdecde pattern that causes the polypeptide chain to fold into two similar motifs. As a hydrophobic core is absent from hirustasin the disulfide bridges maintain the tertiary structure and present the primary binding loop to the active site of the protease. The general structural topography and disulfide connectivity of hirustasin has not previously been described.

CONCLUSIONS

The crystal structure of the kallikrein-hirustasin complex reveals that hirustasin differs from other serine protease inhibitors in its conformation and its disulfide bond connectivity, making it the prototype for a new class of inhibitor. The disulfide pattern shows that the structure consists of two domains, but only the C-terminal domain interacts with the protease. The disulfide pattern of the N-terminal domain is related to the pattern found in other proteins. Kallikrein recognizes hirustasin by the formation of an antiparallel beta sheet between the protease and the inhibitor. The P1 arginine binds in a deep negatively charged pocket of the enzyme. An additional pocket at the periphery of the active site accommodates the sidechain of the P4 valine.

Purification of enzymatically active kallikrein hK2 from human seminal plasma

Kallikrein hK2 is a member of the human glandular kallikrein family which includes prostate-specific antigen (PSA) and pancreatic-renal kallikrein. The purpose of this work was to isolate and characterize for the first time the enzymatically active form of the hK2 protein starting from the PCI-hK2 complex isolated from human seminal plasma (Deperthes, D., Chapdelaine, P., Tremblay, R.R., Brunet, C., Berton, J., Hébert, J., Lazure, C. and Dubé, J.Y. (1995) Biochim. Biophys. Acta 1245, 311-316). That complex was dissociated by an incubation at alkaline pH and final purification was achieved by C-18 reverse phase HPLC. The purified material contained a 27 kDa band by SDS gel electrophoresis and had the expected NH2-terminal amino acid sequence of hK2. It hydrolyzed synthetic chromogenic substrates containing esters of lysine and arginine but not of phenylalanine. Furthermore, hK2 formed molecular complexes with alpha 2 -antiplasmin, alpha 1-antichymotrypsin, antithrombin III and alpha 2-macroglobulin but not with alpha 1-antitrypsin. In conlusion, the new findings of the present paper are that the PCI-hK2 complex can be dissociated by mild procedures, that the free hK2 protein can be purified thereafter by standard HPLC procedures, that the recovered free hK2 is a trypsin-like enzyme and that it can form molecular complexes with many of the major serum proteinase inhibitors.

Homology modelling of rat kallikrein rK9, a member of the tissue kallikrein family: implications for substrate specificity and inhibitor binding

The rat kallikrein rK9 is one of the six members of the rat tissue kallikrein family isolated to date. It is 84% identical to rK2 (tonin), and both proteinases are thought to have vasoconstrictive properties. Recently we have shown that rK9 and rK2 have distinct substrate specificities and sensitivities to inhibitors, despite their similar sequences. Unlike all other mammalian kallikrein-related proteinases, rK9 is resistant to inhibition by aprotinin. We have developed a 3-D model of rK9, based on the known X-ray structures of rK2, porcine kallikrein and bovine trypsin, to identify the structural features underlying this functional diversity. The final rK9 model is structurally similar to rK2, but variable regions surrounding the active site differ quite markedly from the reference proteins. The kallikrein loop, which differs from that in porcine kallikrein by a seven-residue insertion, has been generated de novo and subjected to simulated annealing to assess its influence on the restricted substrate specificity of these proteinases. The proposed conformation of the specificity pocket in rK9 differs from that of other serine proteinases, but it can still accommodate both aromatic and basic amino acid side chains at the substrate P1 position, thus explaining the dual chymotrypsin and trypsin-like activity of rK9. The electrostatic potentials of rK9 and aprotinin were calculated using the finite difference Poisson-Boltzmann method. They indicated a large positive region near the active site of rK9 not found in related proteinases because of positively charged residues at positions 61 and 65 in rK9. They generate a positive region, which overlaps a positive region in aprotinin, and may prevent aprotinin binding. A single mutation in aprotinin is suggested that might allow kallikrein rK9 inhibition by aprotinin. This model contributes significantly to our understanding of the structure-function relationships among proteinases of the tissue kallikrein family.

Isolation and characterization of human tissue kallikrein produced in Escherichia coli: biochemical comparison to the enzymatically inactive prokallikrein and methionyl kallikrein

This report describes bacterial expression, isolation, and characterization of human tissue kallikrein recombinantly produced in Escherichia coli. Successful production of enzymatically active recombinant human kallikrein requires the following processes: expression, solubilization and refolding of prokallikrein, thermolysin activation, and chromatographic separation. All experimental data confirmed that bacterially derived human kallikrein is properly folded and exhibits expected biochemical functions. As confirmed by SDS-PAGE and reverse-phase HPLC, recombinant kallikrein is apparently pure and is devoid of reduced or other partially folded kallikrein forms. Recombinant kallikrein behaves as a monomeric molecule in solution and exhibits full enzymatic activity in hydrolyzing peptide substrates. The molecule can bind to aprotinin to form kallikrein-inhibitor complex at a 1:1 molar ratio. Peptide mapping analysis derived from pepsin digestion of recombinant kallikrein assigned five disulfide bonds which match those of porcine kallikrein predicted from X-ray structure. Peptides containing unpaired cysteines or mispaired disulfide bonds were not detected. Both properly folded prokallikrein and methionyl kallikrein, containing a propeptide and an initiator methionine at their N-termini, respectively, were also produced and isolated. These two molecules are structurally similar to recombinant kallikrein, but are not enzymatically active.

Purification and characterization of human tissue prokallikrein and kallikrein isoforms expressed in Chinese hamster ovary cells

We report here the expression of recombinant human prokallikrein and kallikrein in engineered Chinese hamster ovary cells transfected with a human genomic gene encoding preprokallikrein. At high expression levels, recombinant prokallikrein, an inactive proenzyme form, is predominantly secreted into the culture medium. Upon chromatographic separations, the inactive prokallikrein as well as the mature kallikrein after thermolysin activation of the proenzyme can be prepared to apparent purity. Both prokallikrein and kallikrein can be further separated into two distinct high- and low-molecular-weight isoforms. Kallikrein preparations are fully active in standard kallikrein activity assays such as esterase activity and kinin release from kininogen. Both kallikrein and prokallikrein display multiple molecular forms with differences in both molecular sizes and charges. The structural differences in high- and low-molecular-weight kallikreins or prokallikreins were found to be due to glycosylation, with the high-molecular-weight species glycosylated at three Asn-linked sites and the low-molecular-weight species at two of the three Asn-linked sites. The multiply charged kallikrein isoforms are derived from different numbers of sialic acids attached at the detected Asn-linked carbohydrates. In comparison with kallikrein, prokallikrein appears to show a significant decrease in the magnitude of near uv-circular dichroism bands, suggesting a change in local conformation. This conformational change correlates with the loss of activity in proenzyme due to the presence of propeptide.

7S nerve growth factor is an insulin-like growth factor-binding protein protease

Insulin-like growth factor (IGF)-binding protein (IGFBP) proteases modulate IGF action by cleaving IGFBPs into fragments with lower affinity to IGFs, thereby increasing the levels of free IGFs. We have previously documented that prostate-specific antigen (PSA), a serine protease of the kallikrein family, is an IGFBP-3 protease. In this study, we characterized the potential IGFBP proteolytic activity of nerve growth factor (NGF gamma-subunit), which shares high sequence homology with PSA. [125I]IGFBP-3 was cleaved by NGF (but not other kallikreins) at a 3-fold lower concentration than that of PSA, thus proving NGF to be a more potent IGFBP protease than PSA. NGF-generated, lower mol wt IGFBP-3 fragments, detected by immunoblotting and cross-linking to IGFs, had a lower affinity to IGFs than intact IGFBP-3. Unlike PSA, which cleaves primarily IGFBP-3 and -5, NGF also displayed potent proteolytic activity against IGFBP-4 and -6. These data suggest that NGF may be involved in the growth of cells by more than one mechanism. In addition to binding to its receptors, NGF is capable of cleaving IGFBPs and, thus, enhancing IGF action. This synergistic action between NGF and IGF may have important implications on cell growth, development, and repair in the brain and other tissues.

Immunofluorometric assay for sensitive and specific measurement of human prostatic glandular kallikrein (hK2) in serum

Prostate-specific antigen (PSA) and human prostatic glandular kallikrein (hK2) have 79% identity with the primary structure. When we used recombinant hK2 protein, only 7 of 23 monoclonal anti-PSA IgGs (monoclonal antibodies, MAbs) cross-reacted with hK2, which enabled us to design a novel immunofluorometric MAb-MAb assay for the specific detection of hK2. In the first incubation, an excess of MAb 2H11, which does not cross-react with hK2, is added to prevent both free and complexed PSA from reacting in subsequent immunoreactions. In the second incubation, biotinylated MAb H50, which cross-reacts with hK2 by an epitope overlapping with MAb 2H11, served to bind only hK2 to the microtitration wells coated with streptavidin. In the third step, Eu-labeled MAb H117, which cross-reacts with hK2, detected the immobilized hK2. The hK2 assay was calibrated with recombinant hK2. The detection limit of the assay was 0.1 microgram/L, and the cross-reactivity with recombinant PSA was < or = 0.7%. The concentration of hK2 was measured in serum samples from 334 males with total PSA concentrations ranging from 1 to 3400 microgram/L. Most of the samples (57%) had hK2 concentrations below the detection limit. The proportions of hK2 relative to total PSA were 0-2% in 79%, 2-5% in 14%, 5-10% in 4%, and >10% in 3% of the samples. Gel filtration of 10 serum samples with increased hK2 concentrations showed a single peak of hK2 immunoreactivity with an apparent molecular size of approximately 30 kDa, corresponding to that of recombinant hK2 and free PSA.

The catabolism of intact, reactive centre-cleaved and proteinase-complexed C1 inhibitor in the guinea pig

Clearance rates in the guinea pig were determined for intact guinea pig and human C1 inhibitor, the complexes of both inhibitors with human Cls, beta factor XIIa and kallikrein, and for each inhibitor cleaved at its reactive centre with trypsin. Intact human and guinea pig C1 inhibitor were cleared from the circulation more slowly (t1/2s of 9-7 h and 12.1 h and fractional catabolic rates (FCRs) of 0.09 and 0.117) than any of their cleaved or complexed forms. The reactive centre-cleaved inhibitors were cleared with half-lives of 6.75 h for humans and 10.1 h for the guinea pig. The complexes with target proteases were catabolized much more rapidly, with half-lives ranging from 3-08 h to 4.3 h. The complexes with kallikrein were cleared more slowly than those with Cls and beta factor XIIa. Complexes prepared with the guinea pig and human inhibitors were cleared at equivalent rates. The free inactivated proteases were cleared at rates similar to the equivalent complexes, except for kallikrein, which was cleared more rapidly than its complex. The fact that the complexes with different target proteases differed in their catabolism and that protease and complex catabolism were similar suggests that protease may play a direct role in clearance.

Plant serine proteinase inhibitors. Structure and biochemical applications on plasma kallikrein and related enzymes

The action of two Bowman-Birk and several plant Kunitz-type inhibitors were studied on trypsin, chymotrypsin, plasma kallikrein and factor XII. The primary structure of some of them was completely defined. The results showed that the Bowman-Birk type inhibitors, although potent inhibitors for trypsin (Ki in the range of 1-2 nM), are not able to inhibit plasma kallikrein. Factor XII (Ki = 1.4 microM) and chymotrypsin (Ki = 5.0 nM) are inhibited by Torresea cearensis trypsin inhibitor (TcTI) but not by Dioclea glabra trypsin inhibitor (DgTI). Both inhibitors reactive site regions are highly homologous, and the amino acid residues in P1 position are the same, Lys and His; major differences are in the charge of the C-terminal portion of the molecules. The studied Kunitz-type inhibitors were all able to inhibit plasma kallikrein (Ki between 4 and 80 nM), with the exception of Schizolobium parahyba chymotrypsin inhibitor (SpCI), that is specific for chymotrypsin. All Kunitz-type inhibitors inactivate chymotrypsin, but with a dissociation constant in the range of 0.1 to 0.6 microM. Factor XIIf is inhibited with Ki in the range of 0.1 microM. Bauhinia bauhinioides trypsin inhibitor (BbTI) did not promote factor XIIf inhibition. The Kunitz-type inhibitors are a highly homologous, sharing 60% identity in the N-terminal portion of the loop containing the reactive site, and 28.6% identity in the C-terminal portion of the same loop.

Comparative study of kallikrein-like serine proteinases from rat submandibular glands

The present investigation describes the comparative properties, particularly the substrate specificity of three kallikrein-like serine proteinases (I, II and III) purified from rat submandibular gland extract (Bedi, G.S., Prep. Biochem. 22,67-81, 1992). The physico-chemical and immunological properties of three proteinases were compared by Western blot analysis, immunodiffusion, immuno-electrophoresis, amino terminal sequence analysis, molecular weight determination and isoelectric focusing. Detailed substrate specificity of these proteinases was determined using chromogenic substrates, synthetic peptides and native proteins. The chromogenic substrate tosyl-gly-pro-arg-pNA was hydrolyzed preferentially by Proteinase I. The replacement of pro at the P2 position with bulky hydrophobic residues phe and leu completely abolished the hydrolysis by Proteinase I. The hydrolysis of the chromogenic substrates by Proteinase II was also affected by the amino acid residue present at the P2 position in the order of pro > gly > val > leu > phe. Neither Proteinase I nor Proteinase II hydrolyzed substrates in which arg was replaced with lys at the P1 position. Proteinase III was reactive against all the chromogenic substrates with arg or lys at the P1 position. Synthetic polypeptides T-kinin-leu and insulin B chain were resistant to cleavage by both Proteinase I and II and were cleaved specifically at arg-X peptide bond by Proteinase III. Tonin-like activity of Proteinase II was confirmed by cleavage of the angiotensin 1-14 at phe-his linkage to generate two fragments DRVYIHPF and HLLVYS respectively. All three proteinases cleaved human high molecular weight kininogen but only Proteinase III could cleave T-kininogen. Proteinase III was also reactive towards human and bovine fibronectin, fibrinogen and gelatin. Several other salivary and serum proteins were resistant to cleavage by these proteinases. Although the three enzymes are immunologically related, they differ with respect to size, isoelectric point, amino terminal sequence and inhibition profile.

rK7-kallikrein in rat kidney and urine

Rat Kidney is reported to contain the rK7-kallikrein gene expressed at a high mRNA level. However, there is no direct evidence that the rK7 enzyme is present in kidney or urine. We have analyzed rat kidney and urine for rK7-like enzyme activity, using distinctive properties of purified rK7 enzyme (hydrolysis of specific substrate, inhibition by SBTI). Rat urine and kidney cortex contain substantial levels of rK7-like enzyme activity. Nearly 40% of the enzyme in urine is in an active form while nearly all of the rK7 in kidney cortex is in the inactive form. Treatment with low salt diet and mineralocorticoid increases rK7 in both kidney cortex and urine approximately 2-fold. The percentage of active enzyme in urine increases markedly on this regimen.

Use of lectin-probes for correlative histochemical and biochemical assessments of the glycosylation patterns of secretory proteins, including kallikreins, in salivary glands and saliva

Labelled lectins were used as probes to study the glycosylation and secretion of submandibular glycoproteins not only in sections of fixed glands but also in glandular extracts and in nerve-induced saliva, after electrophoretic separations and immobilization in nitrocellulose membranes. In cats the glycoproteins in sympathetic saliva differed considerably from those in parasympathetic saliva. In sympathetic saliva they were found to originate mainly from striated ducts, to some extent from demilunar cells and to a small extent from acinar cells, whereas in parasympathetic saliva they arose mainly from acinar cells and demilunes and only to a small extent from striated ducts. In rat submandibular glands sympathetic stimulation caused extensive depletion of lectin stainable granules from granular tubules. Corresponding strong binding occurred with the same lectins to constituents in saliva that ran between 25 and 35 kD on SDS gel electrophoresis and were shown to contain tissue kallikreins. Their binding patterns suggested that individual kallikreins from the same gland may be glycosylated in different ways. This possibility was tested on five different kallikreins after separation from submandibular extracts by isoelectric focussing. Lectin bindings on slot blot preparations of these kallikreins were tested before and after N-glycosidase F, sialidase or endo-alpha-N-acetylgalactosaminidase digestions. Results showed that, despite their close genetic and structural similarities, the kallikreins are in fact differently sialylated and fucosylated and the novel finding that some contain O-glycosidically linked side chains as well as the anticipated N-glycosidically linked side chains was revealed. Thus, correlative histochemical and biochemical assessments of bindings with lectin probes has provided important new information about differences in the glycosylation patterns of individual glycoproteins stored within the same secretory granules.

Differences in the glycosylation of rat submandibular kallikreins

The glycosylations of five different rat submandibular kallikreins, rK1, rK2, rK7, rK9 and rK10, vacuum-blotted onto nitrocellulose membranes, have been studied by means of labelled lectins using enhanced chemiluminescence detection. The results demonstrated the individual submandibular kallikreins are not heavily glycosylated in rats, but consistently show different patterns of glycosylation. Following digestion of slot-blotted enzymes with peptide-N-glycosidase F (PNGase): binding by lectin from Lens culinaris (alpha Man-directed) was abolished, whilst that of lectin from Maclura pomifera (Gal beta 1,3GalNAc-directed) persisted (but could be abolished by periodate oxidation and endo-alpha-N-acetylgalactosaminidase digestion), revealing that there are O- as well as N-linked sugar chains on the kallikreins; a novel observation for this family of enzymes. The presence of GalNAc in addition to GlcNAc, Fuc, Gal, and Man, in sugar chains of rK1 was confirmed by high pH anion exchange chromatography following acid hydrolysis. Different intensities of binding by lectin from Limax flavus (NeuNAc-directed) suggest that sialylation of individual kallikreins differs, whilst sialidase and PNGase digestions suggest that sialic acid is the terminal residue of some N-linked but not O-linked structures.

Evaluation of the extent of the binding site in human tissue kallikrein by synthetic substrates with sequences of human kininogen fragments

We have synthesized internally quenched peptides spanning the Met379-Lys380 or Arg389-Ser390 bonds of human kininogen (hkng) that flank lysyl-bradykinin and have studied the kinetics of their hydrolysis by human tissue kallikrein. The kinetic data for the hydrolysis of the Met-Lys bond in substrates with an N-terminal extension showed that interactions up to position residue P10 contribute to the efficiency of cleavage. In contrast, there were no significant variations in the kinetic data for the hydrolysis of substrates with C-terminal extensions at sites P'4 to P'11. A similar pattern was observed for the cleavage of substrates containing an Arg-Ser bond because substrates extended up to residue P6 were hydrolysed with the highest kcat/Km values in the series, whereas those extended to P'11 on the C-terminal side had a lower susceptibility to hydrolysis. Time-course studies of hydrolysis by human and porcine tissue kallikreins of a Leu373 to Ile393 human kininogen fragment containing omicron-aminobenzoic acid (Abz) at the N-terminus and an amidated C-terminal carboxyl group Abz-Leu-Gly-Met-Ile-Ser-Leu-Met-Lys-Arg- Pro-Pro-Gly-Phe-Ser-Pro-Phe-Arg-Ser-Ser-Arg-Ile-NH2 (Abz-[Leu373-Ile393]-hkng-NH2) indicated that the cleavage of Met-Lys and Arg-Ser bonds in the same molecule occurs via the formation of independent enzyme-substrate complexes. The hydrolysis of Abz-F-R-S-S-R-Q-EDDnp [where EDDnp is N-(2,4-dinitrophenyl)ethylenediamine] and Abz-M-I-S-L-M-K-R-P-Q-EDDnp by human tissue kallikrein had maximal kcat/Km values at pH 9-9.5 for both substrates. The pH-dependent variations in this kinetic parameter were almost exclusively due to variations in kcat. A significant decrease in kcat/Km values was observed for the hydrolysis of Arg-Ser and Met-Lys bonds in the presence of 0.1 M NaCl. Because this effect was closely related to an increase in Km, it is likely that sodium competes with the positive charges of the substrate side chains for the same enzyme subsites.

Isolation and characterization of a protein corresponding to mKlk-11 clone from male mouse submandibular gland

A protein corresponding to the predicted genomic sequence of clone mKlk-11 has been characterized from mouse submandibular gland. This protein was purified by reverse-phase high-performance liquid chromatography from the submandibular glands of normal and hypertensive mice. The protein was not detected in the submandibular gland of mice selected for low blood pressure. It consists of three fragments starting at the residues 1, 98, and 141 of the predicted sequence of clone mKlk-11. The cleavage of beta-lactoglobulin (between residues 20 and 21, Tyr-Ser, and 40 and 41, Arg-Val) and a synthetic renin substrate tetradecapeptide (residues 4 and 5, Tyr-Ile) by the protein corresponding to clone mKlk-11 showed both tryptic- and chymotryptic-type cleavages. The possibility of this protein's involvement in the regulation of local blood flow is raised.

Purification and characterization of tissue kallikrein-like proteinases from the black sea bass (Centropristis striata) and the southern frog (Rana berlandieri)

Serine proteinases were isolated from the pyloric caeca of the black sea bass (Centropristis striata) and the pancreas of the Southern frog (Rana berlandieri) and were purified to apparent homogeneity by aprotinin affinity column chromatography, reverse phase high performance liquid chromatography and gel filtration FPLC liquid chromatography to produce products with molecular masses of approximately 27,000 Da and isoelectric points from 4.2 to 5.0. Both enzymes were kallikrein-like and were bound by diisopropylfluorophosphate; had pH optima from 9 to 10; showed high specificity for the hydrolysis of arginine peptide bonds and low to moderate affinity for lysine bonds at the P1 substrate recognition sites; were inhibited by aprotinin, benzamidine, leupeptin, and soybean trypsin inhibitor; generated kinin from kininogen and were highly stable at room temperature. Differences between the enzymes were observed relative to their hydrophobicities, substrate specificities, stabilities at acidic pHs in the presence and absence of calcium, and the amounts of kinin generated from kininogen. Many of the fish trypsins, previously identified as anionic trypsins, may actually be more kallikrein-like.

Identification of glandular kallikrein in dog pancreas and determination of its tissue distribution

In order to establish a formal link between previously purified canine urinary kallikrein and dog pancreatic kallikrein whose cDNA sequence has recently been published, we have isolated the pancreatic kallikrein from that animal species. Pancreatic cytosol proteins were sequentially subjected to chromatography on DEAE-Sepharose CL-6B and Concanavalin A-Sepharose, to an autolysis step and finally to two-dimensional gel electrophoresis. Kallikrein immunoreactive spots were identified with an antibody directed against canine urinary kallikrein. These proteins were isolated after electroblotting and the amino acid sequence of their NH2-terminal portion was determined by microsequencing. The sequence was found to be identical to the one deduced from pancreatic kallikrein cDNA. Using the same antibody and immunohistochemical procedures, kallikrein was found to be present in the pancreas, the salivary glands, the kidney, the colon, the lungs and the testis. These results thus confirm the molecular nature of a glandular kallikrein in the canine species.

Inhibition of bovine beta-trypsin, human alpha-thrombin and porcine pancreatic beta-kallikrein-B by 4',6-diamidino-2-phenylindole, 6-amidinoindole and benzamidine: a comparative thermodynamic and X-ray structural study

The inhibitory effect of 4',6-diamidino-2-phenylindole (DAPI) and 6-amidinoindole on the catalytic properties of bovine beta-trypsin (trypsin), human alpha-thrombin (thrombin) and porcine pancreatic beta-kallikrein-B (kallikrein) was investigated (between pH 3.0 and 7.0, I = 0.1 M; T = 30.0 +/- 0.5 degrees C), and analyzed in parallel with that of benzamidine, commonly taken as a molecular inhibitor model of serine proteinases. Next, the X-ray crystal structure of the trypsin:DAPI complex was solved at 1.9 A resolution (R = 0.161). Over the whole pH range explored, values of the association inhibition constant (Ki) for DAPI and 6-amidinoindole binding to trypsin, thrombin and kallikrein are higher than those found for benzamidine association, suggesting a binding mode of DAPI to the enzyme primary specificity pocket-based on the indole moiety of the inhibitor. On lowering the pH from 5.5 to 3.0, the decrease in affinity for DAPI, 6-amidinoindole and benzamidine binding to trypsin, thrombin and kallikrein reflects the acidic pK shift of the Asp189 invariant residue, present at the bottom of the primary specificity subsite of the serine proteinases considered, from 4.5, in the free enzyme, to 3.7, in the proteinase:inhibitor complexes. Inspection of the refined crystal structure of the trypsin:DAPI complex, however, does not allow a unique interpretation of the inhibitor binding mode. The present data were analysed in parallel with those reported for related serine (pro)enzyme/inhibitor systems.

Modeling of prostate specific antigen and human glandular kallikrein structures

The three dimensional structures of human prostate specific antigen (PSA) and glandular kallikrein (hGK) were modeled based on porcine pancreatic kallikrein A. High sequence similarity and conserved framework of serine proteases enabled accurate modeling. The catalytic site region consisting of catalytic triad, residues forming oxyanion hole and main-chain substrate binding residues were conserved. The substrate specificity pocket of PSA resembles that of chymotrypsin and hGK is most related with tonin. The models were used to predict interactions with substrate and inhibitor molecules. The models are valuable in interpreting mutant and epitope mapping data as well as when modifying properties of the proteases or when developing diagnostic detection methods for prostatic cancer.

Classification of serine proteases derived from steric comparisons of their active sites, part II: "Ser, His, Asp arrangements in proteolytic and nonproteolytic proteins"

The assignment of serine proteases to the families of (chymo)trypsins and subtilisins, respectively, is extended by including additional data from the Brookhaven Protein Data Bank. To better understand basic properties connected with this type of assignment the steric situation in the vicinity of the tetrad aminoacyl residues and atomic distances within the tetrads are considered. A new catalytic mechanism is suggested based on differences between tonin and kallikrein with respect to structure and reactivity of the catalytic tetrad. All protein structures available from the Brookhaven Protein Data Bank are analyzed with regard to the occurrence of Asp....His....Ser triads.

A structural model for the prostate disease marker, human prostate-specific antigen

Prostate-specific antigen (PSA) provides an excellent serum marker for prostate cancer, the most frequent form of cancer in American males. PSA is a 237-residue protease based on sequence homology to kallikrein-like enzymes. To predict the 3-dimensional structure of PSA, homology modeling studies were performed based on sequence and structural alignments with tonin, pancreatic kallikrein, chymotrypsin, and trypsin. The structurally conserved regions of the 4 reference X-ray proteins provided the core structure of PSA, whereas the loop structures were modeled on the loops of tonin and kallikrein. The unique "kallikrein loop" insert, between Ser 95b and Pro 95k of kallikrein, was constructed using molecular mechanics, dynamics, and electrostatics calculations. In the resulting PSA structure, the catalytic triad, involving residues His 57, Asp 102, and Ser 195, and hydrophobic and electrostatic interactions typical of serine proteases were extremely well conserved. Similarly, the 5-disulfide bonds of kallikrein were also conserved in PSA. These results, together with the fact that no major steric clashes arose during the modeling process, provide strong evidence for the validity of the PSA model. Calculation of the electrostatic potential contours of kallikrein and PSA was carried out using the finite difference Poisson-Boltzmann method. The calculations revealed matching areas of negative potential near the catalytic triad, but differences in the positive potential surrounding the active site. The PSA glycosylation site, Asn 61, is fully accessible to the solvent and is enclosed in a positive region of the isopotential map. The bottom of the substrate specificity pocket, residue S1, is a serine (Ser 189) as in chymotrypsin, rather than aspartate (Asp 189) as in tonin, kallikrein, and trypsin. This fact, plus other features of the S1 binding-pocket region, suggest that PSA would prefer substrates with hydrophobic residues at the P1 position. The location of a potential zinc ion binding site involving the side chain of histidines 91, 101, and 233 is also suggested. This PSA model should facilitate the understanding and prediction of structural and functional properties of this important cancer marker.

Purification and characterization of a novel substrate for plasma kallikrein (PK-120) in human plasma

A 120 kDa plasma protein, which is susceptible to plasma kallikrein, was purified from human plasma by polyethylene glycol fractionation followed by ion exchange chromatography using Q-Sepharose, S-Sepharose, and hydroxyapatite and gel filtration on Sephacryl S-200. The 120 kDa protein, termed PK-120 in this paper, was a single polypeptide chain containing about 20% sugar by weight and its concentration in plasma was estimated to be 80 micrograms/ml by ELISA. At least three fragments, 100, 70, and 35 kDa, were produced from PK-120 by plasma kallikrein. The N-terminal sequence and Western blot demonstrated that PK-120 was first cleaved to yield the 100 and 35 kDa fragments, then the 100 kDa fragment was cleaved into the 70 kDa fragment. N-Terminal sequence analyses of PK-120 and its fragments demonstrated that it is a novel plasma protein, distinct from high molecular weight kininogen, a natural substrate for plasma kallikrein.

Functional analysis of the serpin domain of C1 inhibitor

To analyze the role of the heavily glycosylated amino-terminal domain of C1 inhibitor in protease inhibitory activity, two truncated C1 inhibitor molecules were constructed. The abilities of the recombinant truncated inhibitors to complex with target proteases were compared with that of the wild-type recombinant protein. One recombinant truncated molecule consisted of amino acid residues 76 to 478 (C-serp(76)) and the other of residues 98 to 478 (C-serp(98)). The recombinant proteins were each expressed in similar quantities. The thermal denaturation profiles of the two truncated proteins were similar to that of the wild-type protein. Identical binding of C1s, C1r, kallikrein, and beta factor XIIa was observed with the three molecules. Furthermore, the truncated molecules also effectively inhibited C1 activity in hemolytic assays. These studies therefore clearly demonstrate that the amino-terminal domain of C1 inhibitor does not influence complex formation with target proteases.

Localization of the binding site on plasma kallikrein for high-molecular-weight kininogen to both apple 1 and apple 4 domains of the heavy chain

The C-terminal end of the heavy chain of human plasma prekallikrein or kallikrein contains a binding site for high-molecular-weight kininogen, the nonenzymatic procofactor of contact activation. To further map this binding site, a series of overlapping peptides were synthesized. The amount of kallikrein that bound to kininogen-coated microtiter plate wells in the presence of increasing concentrations of each peptide was determined by kallikrein amidolytic activity. A peptide encompassing Lys266-Gly295 of kallikrein, conformationally constrained by a disulfide bond, displayed the lowest Kd value (approximately 67 microM). The linear peptide, Leu262-Gly295, displayed lower affinity (129 microM). N-terminal or C-terminal truncation/extension peptides of this sequence diminished binding activity. Since the closely related protein, factor XI, has been shown to bind kininogen, a kallikrein-based peptide (Phe56-Gly86) homologous to the binding domain of FXI, was examined and found to possess less, but significant, binding affinity for kininogen (Kd 530 microM). Isothermal titration calorimetry was used to assess binding between the kallikrein-based peptides and a peptide encompassing the kallikrein binding domain in kininogen (Ser565-Lys595). Leu262-Gly295 possesses potent binding activity (Kd 52 microM), while Phe56-Gly86 displays poorer binding activity (Kd 400 microM). These interactions are endothermic and entropically favored, suggesting that a conformational rearrangement takes place upon binding. We conclude that the binding site for kininogen within prekallikrein is composed of discontinuous linear segments that form a contiguous surface in the folded protein.

Multiple copy sampling: rigid versus flexible protein

Effects of protein flexibility on multiple copy conformational sampling were systematically evaluated by studying the side-chain placement of Phe-14 in protein Zif268. The multiple copy sampling is shown to be significantly more efficient when a flexible but harmonically constrained protein is used instead of a rigid protein. A range of constraint force from 1 to 25 kcal/mol.A per atom is determined to be sufficient to prevent the protein from distortion while allowing the protein to fluctuate for enhanced sampling. The protein fluctuations are essential in smoothing the effective energy surface as shown by the opening-closing of a protein hydrophobic pocket during a multiple copy energy minimization, a phenomenon that has been previously observed only in molecular dynamics. These results provide a practical guidance for applying the multiple copy techniques to molecular modeling and computer-aided drug design.

Isolation and properties of a T-kininogenase from bovine erythrocyte membranes

A kininogenase from bovine erythrocyte membranes has been purified 140-fold by affinity chromatography on pepstatin A-Agarose followed by ion exchange chromatography on CM Cellulose. The purified enzyme showed an apparent molecular weight of 31,000 daltons as measured by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Its pH optimum is 7.5, and it was totally inhibited by soybean trypsin inhibitor, phenylmethyl-sulfonylfluoride, aprotinin, pepstatin, and dithiotreitol, suggesting the presence of a disulfide bond(s) whose integrity is(are) essential for maintaining the native three-dimensional structure. The referred enzyme was able to release kinin from a substrate partially purified from rat plasma. The kininogenase was activated by Zn2+, Ca2+, and cysteine-HCl.

In vitro plasma protein adsorption and kallikrein formation on 3-mercaptopropionic acid, L-cysteine and glutathione immobilized onto gold

3-Mercaptopropionic acid (MPA), L-cysteine (L-cys), and glutathione (GSH) monolayers were immobilized onto gold and used in in vitro protein tests. The surfaces were characterized with ellipsometry, static contact angle measurements, atomic force microscopy, and Fourier transform infrared reflection absorption spectroscopy (FT-IRAS). After incubations in human plasma and antibody solutions, the surface antisera binding patterns were determined with ellipsometry. Using serum instead of plasma, complement activation was studied in the same fashion. Activated coagulation Factor XII and kallikrein formation on the surfaces and in the plasma were studied using a kallikrein-specific colorimetric assay. 3-Mercaptopropionic acid indicated contact activation of coagulation but L-cysteine did not. Glutathione displayed low deposition of plasma proteins, large deposition of proteins from serum, and did not promote kallikrein formation. None of the surfaces could be attributed complement activating properties, as determined by antibody deposition. The present study demonstrates that surface biology in complex model systems can be conveniently studied in vitro through systematic and well defined surface modifications.

Binding of native and [homoserine lactone-52]-52,53-seco-bovine basic pancreatic trypsin inhibitor (Kunitz inhibitor) to porcine pancreatic beta-kallikrein-B and bovine alpha-chymotrypsin: thermodynamic study

Values of the association equilibrium constant (Ka) for the binding of the native and of the cyanogen bromide-cleaved bovine basic pancreatic trypsin inhibitor (native BPTI and [Hse lactone-52]-52,53-seco-BPTI, respectively) to neuraminidase-treated porcine pancreatic beta-kallikrein-B (kallikrein) and bovine alpha-chymotrypsin (chymotrypsin) have been determined between pH 4.0 and 9.0, at 20.0 degrees C. Over the whole pH range explored, native BPTI and [Hse lactone-52]-52,53-seco-BPTI show the same affinity for kallikrein. On the other hand, the affinity of [Hse lactone-52]-52,53-seco-BPTI for chymotrypsin is higher, around neutrality, than that found for native BPTI by about one order of magnitude, converging in the acidic pH limb. The simplest mechanism accounting for the observed data implies that, on lowering the pH from 9.0 to 4.0, (i) the decrease in affinity for the binding of native BPTI to kallikrein and chymotrypsin, as well as for the association of [Hse lactone-52]-52,53-seco-BPTI to kallikrein, reflects the acidic pK shift, upon inhibitor association, of a single ionizing group; and (ii) the decrease of Ka values for [Hse lactone-52]-52,53-seco-BPTI binding to chymotrypsin appears to be modulated by the acidic pK shift, upon inhibitor association, of two non-equivalent proton-binding residues. On the basis of the stereochemistry of the serine proteinase/inhibitor contact region(s), these data indicate that long-range structural changes in [Hse lactone-52]-52,53-seco-BPTI are energetically linked to the chymotrypsin:inhibitor complex formation. This observation represents an important aspect for the mechanism of molecular recognition and regulation in BPTI.

Purification by HPLC anion-exchange chromatography and some properties of a kinin-releasing enzyme from the venom of Agkistrodon halys ussuriensis

A kinin-releasing enzyme was isolated from the venom of Agkistrodon halys ussuriensis using a very convenient two-step procedure consisting of HPLC anion-exchange chromatography. The relative molecular mass was estimated as 24,000 by SDS gel electrophoresis and an isoelectric point of pH 3.7 was established by gel isoelectric focusing. The kinin-releasing enzyme resembled a typical tissue kallikrein in the values of such physiochemical parameters, in its thermal stability, in its lack of activity towards fibrinogen and casein, and in its behaviour with potential inhibitors. Thus, the enzyme can be classified as a kallikrein-like enzyme.

Identification of mK1, a true tissue (glandular) kallikrein of mouse submandibular gland: tissue distribution and a comparison of kinin-releasing activity with other submandibular kallikreins

The protein structure, kinin-releasing activity, and tissue distribution of four major proteinases of mouse submandibular gland (mK22, mK9, proteinase F, proteinase P) were studied. When compared with the deduced amino acid sequence of each member of the tissue (glandular) kallikrein gene family, the amino acid sequence of proteinase F determined (approximately 40% of the total) was found to agree completely with the deduced amino acid sequence of mKlk-1. The proteinase P sequence, on the other hand, agreed with that of the product of mKlk-13, mK13 (prorenin-converting enzyme). Proteinase F had the strongest kininogenase activity for both low-molecular-weight and high-molecular-weight kininogen, while mK22 had 1/6 and 1/50 the activity of proteinase F for the respective kininogen substrate. Kininogenase activities of mK9 and proteinase P were less than 1/100 of the activity of proteinase F for both substrates. Acting on the two kininogen substrates, kallikreins mK22, mK9, and proteinase F, but not proteinase P, specifically released bradykinin, suggesting that the former three kallikreins strictly recognized peptide sequences around bradykinin in these substrate molecules but proteinase P recognized several sites in these molecules. Significant amounts of proteinase F, but not mK22 and others, were present in the urine, pancreas and digestive organs, as well as in the salivary glands. The present results revealed that the former proteinase F is identical to mK1, tissue/renal kallikrein, and confirmed its characteristics as a true kallikrein on the basis of its kinin-releasing activity and tissue distribution.

Comparative protein modelling by satisfaction of spatial restraints

We describe a comparative protein modelling method designed to find the most probable structure for a sequence given its alignment with related structures. The three-dimensional (3D) model is obtained by optimally satisfying spatial restraints derived from the alignment and expressed as probability density functions (pdfs) for the features restrained. For example, the probabilities for main-chain conformations of a modelled residue may be restrained by its residue type, main-chain conformation of an equivalent residue in a related protein, and the local similarity between the two sequences. Several such pdfs are obtained from the correlations between structural features in 17 families of homologous proteins which have been aligned on the basis of their 3D structures. The pdfs restrain C alpha-C alpha distances, main-chain N-O distances, main-chain and side-chain dihedral angles. A smoothing procedure is used in the derivation of these relationships to minimize the problem of a sparse database. The 3D model of a protein is obtained by optimization of the molecular pdf such that the model violates the input restraints as little as possible. The molecular pdf is derived as a combination of pdfs restraining individual spatial features of the whole molecule. The optimization procedure is a variable target function method that applies the conjugate gradients algorithm to positions of all non-hydrogen atoms. The method is automated and is illustrated by the modelling of trypsin from two other serine proteinases.