Bovine and human plasma prekallikrein

Heparin modulation of human plasma kallikrein on different substrates and inhibitors

The interplay of different proteases and glycosaminoglycans is able to modulate the activity of the enzymes and to affect their structures. Human plasma kallikrein (huPK) is a proteolytic enzyme involved in intrinsic blood clotting, the kallikrein-kinin system and fibrinolysis. We investigated the effect of heparin on the action, inhibition and secondary structure of huPK. The catalytic efficiency for the hydrolysis of substrates by huPK was determined by Michaelis-Menten kinetic plots: 5.12x10(4) M-1 s-1 for acetyl-Phe-Arg-p-nitroanilide, 1.40x10(5) M-1 s-1 for H-D-Pro-Phe-Arg-p-nitroanilide, 2.25x10(4) M-1 s-1 for Abz-Gly-Phe-Ser-Pro-Phe-Arg-Ser-Ser-Arg-Gln-EDDnp, 4.24x10(2)M-1 s-1 for factor XII and 5.58x10(2) M-1 s-1 for plasminogen. Heparin reduced the hydrolysis of synthetic substrates (by 2.0-fold), but enhanced factor XII and plasminogen hydrolysis (7.7- and 1.4-fold, respectively). The second-order rate constants for inhibition of huPK by antithrombin and C1-inhibitor were 2.40x10(2) M-1 s-1 and 1.70x10(4) M-1 s-1, respectively. Heparin improved the inhibition of huPK by these inhibitors (3.4- and 1.4-fold). Despite the fact that huPK was able to bind to a heparin-Sepharose matrix, its secondary structure was not modified by heparin, as monitored by circular dichroism. These actions may have a function in the control or maintenance of some pathophysiological processes in which huPK participates.

Activity of an enzyme converting single-chain tissue-type plasminogen activator to the two-chain form in preovulatory human follicular fluid

The biological role of the tissue-type plasminogen activator (tPA)/plasmin system has long been implicated in ovarian function. We have recently shown that the follicular fluid of human ovaries contains an alpha(2)-macroglobulin/protease complex capable of converting single-chain (sc) tPA to the two-chain (tc) enzyme tPA, suggesting the occurrence of its corresponding enzyme in a free form in the fluid. The aim of the current study is therefore to gain further information about the putative sctPA-converting enzyme present in follicular fluid. Incubation of human recombinant sctPA with the fluid brought about the production of tctPA. It was also demonstrated that tctPA production resulted in the activation of endogenous fluid plasminogen. Production of tctPA and plasmin both was strongly inhibited by aprotinin, suggesting that the enzyme is a serine protease. The sctPA-converting enzyme was partially purified from the fluid by column chromatographies. The enzyme preferably hydrolyzed synthetic peptide substrates containing arginine at the P(1) position. The enzyme preparation had a protease inhibitor profile similar to that observed with the crude fluid sample. These results clearly demonstrated that follicular fluid contains an enzyme capable of efficiently converting sctPA to tctPA. Discovery of this sctPA-converting enzyme strongly suggests that the tPA/plasmin system in the preovulatory follicle of human ovaries is operated through the proteolytic conversion of sctPA to tctPA rather than being regulated by a fibrin-dependent mechanism.

Characterization of a unique glycosylated anchor endopeptidase that cleaves the LPXTG sequence motif of cell surface proteins of Gram-positive bacteria

The precursors of most surface proteins on Gram-positive bacteria have a C-terminal hydrophobic domain and charged tail, preceded by a conserved LPXTG motif that signals the anchoring process. This motif is the substrate for an enzyme, termed sortase, which has transpeptidation activity resulting in the cleavage of the LPXTG sequence and ultimate attachment of the protein to the peptidoglycan. While screening a group A streptococcal membrane extract for cleavage activity of the LPXTG motif, we identified an enzyme (which we term "LPXTGase") that differs significantly from sortase but also cleaves this motif. The enzyme is heavily glycosylated, which is required for its activity. Amino acid composition and sequence analysis revealed that LPXTGase differs from other enzymes, in that the molecule, which is about 14 kDa in size, has no aromatic amino acids, is rich in alanine, and is 30% composed of uncommon amino acids, suggesting a nonribosomal construction. A similar enzyme found in the membrane extract of Staphylococcus aureus, indicates that this unusual molecule may be common among Gram-positive bacteria. Whereas peptide antibiotics have been reported from bacillus species that also contain unusual amino acids and are synthesized non-ribosomally on amino acid-activating polyenzyme templates, this would be the first reported enzyme that may be similarly synthesized.

Chicken macrophage stimulating protein is a ligand of the receptor protein-tyrosine kinase Sea

Affinity chromatography, employing the extracellular domain of the Sea receptor, was used to enrich Sea-binding proteins from chicken serum. One isolated protein bound both a Sea-immunoglobulin fusion protein and an antisera raised against murine macrophage stimulating protein. Amino-terminal sequencing of the dual-reactive protein yielded sequences which were identical to the predicted alpha and beta subunits of chicken macrophage stimulating protein. The partially purified chicken macrophage stimulating protein caused autophosphorylation of the Sea receptor. Previous work showed that recombinant expression of fully activatible human or mouse macrophage stimulating protein required a specific Cys to Ala substitution (Wahl, R. C., Costigan, V. J., Batac, J. P., Chen, K., Cam, L., Courchesne, P. L., Patterson, S. D. Zhang, K., and Pacifici, R. E. (1997) J. Biol. Chem. 272, 1-4). Therefore, we expressed both the wild type and the specific Cys to Ala form of chicken macrophage stimulating protein as recombinant proteins. After proteolytic activation, only conditioned media from COS cells transfected with the C665A chicken macrophage stimulating protein, but not from wild type chicken macrophage-stimulating protein, or control vector, was detected by the Sea-immunoglobulin fusion protein in Western blotting experiments. Conditioned media containing the C665A chicken macrophage-stimulating protein readily caused Sea phosphorylation, while conditioned media containing the wild type chicken macrophage-stimulating protein was only effective at inducing receptor phosphorylation at high concentrations. In addition to receptor phosphorylation, the C665A chicken macrophage-stimulating protein induced phosphorylation of Shc, Erk1, and Erk 2. We conclude that macrophage-stimulating protein is a ligand of the Sea receptor protein-tyrosine kinase.

Identification and activation of profollipsin, a latent precursor form of porcine follipsin

A latent protease has been identified in column fractions obtained during the purification of the porcine ovarian serine protease follipsin. The latent enzyme was readily activated by trypsin treatment. The trypsin-activated enzyme was purified using a benzamidine-Sepharose 6B column and was shown to be composed of two distinct, covalently associated polypeptides with Mr of 45000 and 32000. This polypeptide chain composition, together with its substrate specificity, inhibition profile using various protease inhibitors, cross-reactivity with anti-follipsin antibody, and ability to activate single-chain precursor tissue plasminogen activator, indicated its identity as porcine follipsin. The activation of the enzyme with trypsin was found to occur by the hydrolysis of an internal peptide bond resulting in a two-chain structure. Thus, we conclude that the latent enzyme is the inactive precursor form (profollipsin) of follipsin. The present study also shows that the follicular fluid of porcine ovary contains a profollipsin-activating enzyme activity.

Separation of proteases: old and new approaches

All methods of protein separations can be applied to proteases. Some emphasis is put in this review on a powerful technique specific to proteases purification: cyclic peptide antibiotics may be seen as general affinity ligands for proteases. Also, some examples of affinity chromatography of proteases on ligands with narrower specificity are given. The special interest of hydrophobic interaction chromatography for proteases purification is discussed. The merits of immobilized dye chromatography for proteases purification and the interest in empirically screening many immobilized dyes, as well as several eluents are discussed.

High-level expression in Escherichia coli and rapid purification of enzymatically active honey bee venom phospholipase A2

Bee venom phospholipase A2 (BV-PLA2) is a hydrolytic enzyme that specifically cleaves the sn-2 acyl bond of phospholipids at the lipid/water interface. The same enzyme is also believed to be responsible for some systemic anaphylactic reactions in bee venom sensitized individuals. To study the structure/function relationships of this enzyme and to define the molecular determinants responsible for its allergenic potential, a synthetic gene encoding the mature form of BV-PLA2 was expressed in Escherichia coli. This enzyme was produced as a fusion protein with a 6xHis-tag on its amino-terminus yielding 40-50 mg of fusion protein per 1 of culture after metal ion affinity chromatography. A kallikrein protease recognition site was engineered between the 6xHis-tag and the amino-terminus of the enzyme allowing isolation of the protein with its correct N-terminus. Recombinant affinity purified BV-PLA2 was refolded, purified to homogeneity, and cleaved with kallikrein, resulting in a final yield of 8-9 mg of active enzyme per 1 of culture. The enzymatic and immunological properties of the recombinant BV-PLA2 are identical to enzyme isolated from bee venom indicating a native-like folding of the protein.

Affinity purification of proteinases by a combination of immobilized peptidyl aldehyde and semicarbazone

D-Phe-Phe-argininal semicarbazone and Tyr-Gly-Gly-Phe-Leu-Arg-argininal semicarbazone were prepared using the solution phase synthesis method and characterized by mass spectrometry and nuclear magnetic resonance spectroscopy. The tripeptide and heptapeptide semicarbazones were individually immobilized on affi-Gel 15 resulting in two affinity columns called S3 and S7, respectively. A third affinity column was obtained by hydrolysing the semicarbazone moiety in column S3 to aldehyde (column A3). Serine proteinases such as trypsin or rat plasma kallikrein almost quantitatively bind to either S3 or A3 affinity columns. Under optimized conditions, more than 97% of trypsin bound to both columns S3 and A3. At a lower ionic strength and higher pH, 80-85% of rat plasma kallikrein bound to the same columns. Elution of both enzymes was achieved using mild conditions at near neutral pH and in the presence of a small amount of denaturant. Both proteinases were identified and characterized by high-performance liquid chromatography, sodium dodecylsulphate polyacrylamide gel electrophoresis and by their substrate specificity and inhibition profiles. A single purification (six-to seven-fold) step using either column S3 or A3 allowed the preparation of pure trypsin from commercial sources. Starting from rat plasma partially purified by a phenyl boronate column, fractionation on the S3 column allowed approximately an 87-fold purification of rat plasma kallikrein. However, serial purification of rat plasma kallikrein on column S7 followed by column A3 resulted in a purification factor of about 455.

Activation mechanism of human Hageman factor-plasma kallikrein-kinin system by Vibrio vulnificus metalloprotease

Vivrio vulnificus, an opportunistic human pathogen, secretes a metalloprotease (VVP). The VVP inoculated into a guinea pig is known to generate bradykinin through activation of the Hageman factor-plasma kallikrein-kinin system. VVP was shown to possess the ability to activate the human system through the same mechanism as that clarified in the guinea pig system, namely, VVP converted both human zymogens (Hageman factor and plasma prekallikrein) to active enzymes (activated Hageman factor and plasma kallikrein), and the then generated kallikrein liberated bradykinin from high-molecular-weight kininogen. However, in the presence of plasma alpha 2-macroglobulin (alpha 2M), the VVP action was drastically decreased. This finding suggests that the human system might be activated only at the interstitial-tissue space which contains negligible amounts of alpha 2M or in the bloodstream of the individuals whose plasma alpha 2M level is extremely reduced.

Expression and sorting of rat plasma kallikrein in POMC-producing AtT-20 cells

A vaccinia virus (VV) vector was used to express rat plasma kallikrein (rPK) in the constitutively secreting cells, BSC-40, and in the endocrine regulated cells, AtT-20. Using a specific rPK antibody and a fluorogenic substrate, Phe-Phe-Arg-AMC, we demonstrated that in both cell lines VV infections resulted in the synthesis of an immunoreactive enzyme predominantly present as a zymogen which can be activated with trypsin. Stimulation of VV:rPK-infected AtT-20 cells with either 5mM 8-bromo-cAMP or 56 mM KCl resulted in a different pattern of rPK and ACTH secretion, strongly suggesting that rPK follows the constitutive secretory pathway. Finally, the 10% rPK activity found within AtT-20 cell extracts had no effect on pro-opiomelanocortin (POMC) processing either intracellularly or extracellularly. The above data show that the biosynthetic machinery of both cell lines analyzed does not allow the efficient activation of plasma prekallikrein. Finally, despite the PK's demonstrated ability to cleave various hormone precursors in vitro at pairs of basic residues, in vivo, we did not obtain evidence that this hepatic enzyme can also act as an intracellular pro-protein processing enzyme.

Mouse plasma kallikrein: cDNA structure, enzyme characterization, and comparison of protein and mRNA levels among species

There is differential regulation of liver mRNA levels of rat (r) and mouse (m) plasma kallikrein (PK), as observed on Northern blots. Affinity purification of mPK and rPK, microsequencing, and radioimmunoassay in either rat or mouse showed that the difference in mRNA levels does not appreciably affect the circulating PK concentration. Nuclear run-off assays demonstrated that the regulation of the mRNA level of PK is post-transcriptionally controlled. Complete cDNA sequence determination of mPK was achieved using a combination of polymerase chain reaction and lambda gt11 library screening procedures. Within the coding region, the overall sequence homology between mPK and rPK is about 91-92% in amino acid and nucleotide sequence. Although the 3' noncoding segment of mPK is shorter than that of rPK, we calculate a 53% homology with a 5% higher A/T content for mPK. The largest difference is found at the 5' end of the mRNAs: whereas rPK is predicted from its gene structure to have a 167-nucleotide leader sequence, mPK is expected to have more than 605 nucleotides, of which the last 291 are very similar to those found in the rPK gene. The regulation of the mRNA stability and/or turnover rate of PK may possibly be affected by its 5' end in a species-dependent manner.

Rat plasma kallikrein: purification, NH2-terminal sequencing and development of a specific radioimmunoassay

Rat plasma kallikrein (rPK) was purified to homogeneity form plasma using affinity and high-performance liquid chromatography techniques, and subjected to NH2-terminal sequencing. The data showed that the sequenced segments of the regulatory (heavy) and catalytic (light) chains of the proteinase, respectively, display 73 and 91% sequence similarity with their counterpart in human plasma kallikrein. This sequence homology in conjunction with the determined molecular structure and inhibitor sensitivity support the identity of the isolated enzyme as plasma kallikrein. A polyclonal antiserum against rPK was obtained after immunization of rabbits with the purified enzyme, and a specific radioimmunoassay was developed. Since Tyr-iodinated rPK was not recognized by the antiserum, two alternative approaches were found to be successful. These included the use of a tracer consisting of rPK modified with either the affinity reagent 125I-labeled DTyr-Glu-Phe-Lys-Arg chloromethyl ketone or with the Bolton Hunter reagent. The usable range of the assay is between 15-150 fmol per tube. The antibody was shown to bind both monomeric and dimeric forms of rPK. Denaturation of the enzyme in sodium dodecyl sulfate does not abolish immune recognition only as long as the regulatory subunit is attached to the catalytic chain. Oxidation or reduction of rPK results in complete loss of immunoreactivity. This observation suggests that perhaps the disulfide linkage of the catalytic and regulatory polypeptides somehow helps to protect the antigenic epitope from denaturation. Alternatively, the epitope(s) recognized by the antibody spans a domain which includes both Tyr and Cys residues necessary for immune recognition.

A new sensitive assay for bovine activated factor XI (factor XIa) using a reconstituted coagulation cascade system

A sensitive assay for quantitating bovine activated Factor XI (Factor XIa) in vitro was developed by measuring the amidolytic activity of thrombin generated in a mixture of Factors XIa, IX and X and prothrombin prepared from bovine source and washed bovine platelets. In this system, the rate of thrombin generation increased linearly with increasing amounts (fmoles) of Factor XIa. The assay system for Factor XIa was not significantly affected by the presence of plasma kallikrein, Factor XIIa, high-molecular-weight kininogen, amylose sulfate or sulfatide within the range of the amounts used for surface-mediated activation of Factor XII, prekallikrein and Factor XI. Following surface-mediated activation of Factor XI, further generation of Factor XIa was blocked by adding freeze-thawed platelets that contain cationic proteins which bind to negatively-charged surfaces (J. Biochem. 97, 139-151, 1985). The method is useful to the kinetic analysis of the surface-mediated activation of Factors XII and XI, although it is not applicable to the activation in plasma.

Possible basis for the apparent surface selectivity of the contact activation of human blood coagulation factor XII

The activation of factor XII by the proteases factor XIIa and kallikrein is known to be greatly enhanced by certain negatively charged surfaces. Studies that compared factor XII surface binding to factor XII activation found that binding alone was insufficient to account for surface enhancement of the activation rate. The temperature dependence of the reaction showed unusual behavior that may be related to the conformational change of factor XII following binding; the rate of factor XII activation had a relatively low temperature optimum (0-47 degrees C) that was sensitive to choice of surface and salt concentration. In temperature studies, below 47 degrees C, the decrease in the activation rate was not related to the thermal denaturation of enzyme or substrate, nor to the choice of activator enzyme (factor XIIa or kallikrein), nor to the species of factor XII (human or bovine) but to a behavior, designated a thermal transition, associated with the surface or the protein-surface interaction. The previously reported surface selectivity of contact activation is possible due to the temperature characteristics and other properties of the thermal transition; a surface that has a low-temperature thermal transition and that is highly sensitive to salt will be a "poor" contact surface under the usual choice of reaction conditions (approximately 150 mM ionic strength and 37 degrees C). However, solution conditions were identified that allowed the following negatively charged surfaces to function, in nearly equal potency, in the activation of factor XII: phosphatidylserine, phosphatidylglycerol, phosphatidic acid, phosphatidylinositol 4-phosphate, heparin, and 5-kDa dextran sulfate, as well as the previously characterized sulfatide and 500-kDa dextran sulfate.(ABSTRACT TRUNCATED AT 250 WORDS)

Recent evolutionary divergence of plasma prekallikrein and factor XI

The evolution in mammals of the zymogens of the contact activation system of coagulation (factor XII, prekallikrein and factor XI) has been investigated. The NH2-terminal sequences of human plasma prekallikrein and the heavy and light chains of kallikrein have been determined and compared with those of bovine prekallikrein and of human and bovine factors XII and XI. The human and bovine NH2-terminal sequences of the light chains (catalytic polypeptide) show striking similarities both among themselves and with those of the catalytic polypeptide chains of other coagulation and digestive proteases, indicating a common origin. Comparison of the NH2-terminal sequences of human prekallikrein with those of the bovine prekallikrein and human bovine factors XIa and XIIa indicates a common origin of the heavy chain of kallikrein and factor XIa, different from that of either factor XIIa or other known amino acid sequences. Ancestral sequences for human and bovine prekallikrein and factor XI, deduced by genetic analysis of the minimum number of base changes indicate that the NH2-terminus of prekallikrein and factor XI have evolved at about the same rate. The estimated time for the gene duplication was about 124 million years ago, a value consistent with the age of the mammals.

Amino acid sequence of human factor XI, a blood coagulation factor with four tandem repeats that are highly homologous with plasma prekallikrein

A lambda gtll cDNA library prepared from human liver poly(A) RNA has been screened with affinity-purified antibody to human factor XI, a blood coagulation factor composed of two identical polypeptide chains linked by a disulfide bond(s). A cDNA insert coding for factor XI was isolated and shown to contain 2097 nucleotides, including 54 nucleotides coding for a leader peptide of 18 amino acids and 1821 nucleotides coding for 607 amino acids that are present in each of the 2 chains of the mature protein. The cDNA for factor XI also contained a stop codon (TGA), a potential polyadenylation or processing sequence (AACAAA), and a poly(A) tail at the 3' end. Five potential N-glycosylation sites were found in each of the two chains of factor XI. The cleavage site for the activation of factor XI by factor XIIa was identified as an internal peptide bond between Arg-369 and Ile-370 in each polypeptide chain. This was based upon the amino acid sequence predicted by the cDNA and the amino acid sequence previously reported for the amino-terminal portion of the light chain of factor XI. Each heavy chain of factor XIa (369 amino acids) was found to contain 4 tandem repeats of 90 (or 91) amino acids plus a short connecting peptide. Each repeat probably forms a separate domain containing three internal disulfide bonds. The light chains of factor XIa (each 238 amino acids) contain the catalytic portion of the enzyme with sequences that are typical of the trypsin family of serine proteases. The amino acid sequence of factor XI shows 58% identity with human plasma prekallikrein.

Proteolytic activation of tissue plasminogen activator by plasma and tissue enzymes

Tissue kallikrein and factor Xa were found to activate tissue plasminogen activator (t-PA) at a rate comparable with that of plasmin. During the activation reaction, the single-chain molecule was converted into a two-chain form. A slight t-PA activating activity was also found in plasma kallikrein. Other activated coagulation factors, factor XIIa, factor XIa, factor IXa, factor VIIa, thrombin and activated protein C had no effect on t-PA activation. t-PA was also activated by a tissue kallikrein-like enzyme that was isolated from the culture medium of melanoma cells. These results indicate that tissue kallikrein and factor Xa may participate in the extrinsic pathway of human fibrinolysis.