Isolation and Characterization of Mouse Coagulation Factor X – Biophysical and Enzymological Properties

Mouse factor X was highly purified from plasma using barium ion precipitation and chromatography on anion-exchange and heparin- agarose affinity chromatography columns. Intact and reduced patterns of mouse factor X in SDS-PAGE were similar to those of human factor X. The specific absorption E 1%/1 cm at 280 nm of mouse factor X was found to be 11.2. Content of carbohydrate moieties of mouse factor X, determined to be 10% by weight, differs both quantitatively and quantitatively from that of human factor X, while the γ-carboxy- glutamic acid (Gla) and β-hydroxy-aspartic acid (β-OH-Asp) content were essentially the same as for human factor X. The amino-terminal amino acid sequences of the light and heavy chains of mouse factor X separated by SDS-PAGE were ANSFF--FKK and SVALXTSDSE, respectively. Underlined residues are non-identical with those of human factor X. Clotting time-based assays using human factor X- deficient plasma as substrate exhibited the following apparent extents of activation of factor X in mouse plasma, using human plasma as the standard: 195% (intrinsic); 200% (extrinsic); and 190% (RVV-X). Using the purified proteins in the same assay systems, the following apparent activation of mouse factor X was demonstrated, compared with human factor X: 195% (intrinsic); 27% (extrinsic); and 41% (RVV-X). These activity profiles suggest that the human extrinsic coagulation pathway functions less efficiently than the corresponding mouse pathway in the activation of mouse factor X. Furthermore, mouse brain thromboplastin satisfactorily replaced rabbit brain thromboplastin in extrinsic activation of factor X in mouse plasma, but not of human plasma or purified mouse or human factor X, in line with studies by others suggesting that human factor Vila poorly activates factor X in the presence of mouse tissue factor. While fully RVV-X-activated mouse factor X activated human prothrombin at a rate equal to about 117% of that for human factor X, it hydrolyzed the synthetic substrate, S-2222, at a rate of only about 18% of that for human factor X. These results are expected to be useful in making the mouse suitable for study of the mammalian blood coagulation pathways.

Substrate effect on thermal stability of superconductor thin films in the peritectic melting

Systematic experiments were performed by in situ observation of the YBa(2)Cu(3)O(z) (Y123 or YBCO) melting. Remarkably, the superheating phenomenon was identified to exist in all commonly used YBCO thin films, that is, films deposited on MgO, LaAlO(3) (LAO), and SrTiO(3) (STO) substrates, suggesting a universal superheating mode of the YBCO film. Distinctively, YBCO/LAO films were found to possess the highest level of superheating, over 100 K, mainly attributed to the lattice match effect of LAO substrate, that is, its superior lattice fit with Y123 delaying the Y123 dissolving and inferior lattice matching with Y(2)BaCuO(5) (Y211) delaying the Y211 nucleation. Moreover, strong dependence of the thermal stability on the substrate material for Y123 films was also found to be associated with the substrate wettability by the liquid and the potential element doping from the substrate. Most importantly, the understanding of the superheating behavior is widely valid for more film/substrate constructions that have the same nature as the YBCO film/substrate.

Evaluation of anti-activated protein C antibody development in patients with severe sepsis from four clinical studies with drotrecogin alpha (activated)

BACKGROUND

Drotrecogin alpha (activated) (DAA) is a recombinant human activated protein C (APC), which is an antithrombotic protein.

OBJECTIVES

To evaluate the development of anti-APC antibodies in severe sepsis patients in DAA clinical studies.

PATIENTS AND METHODS

Serum and plasma samples were collected in placebo-controlled studies (PROWESS, ADDRESS) and studies where all patients were DAA-treated (ENHANCE, XPRESS). An enzyme-linked immunosorbent assay detecting anti-APC IgA/IgG/IgM antibodies was used. IgG isolated from plasma of positive samples was tested for neutralizing activity against DAA-induced prolongation of activated partial thromboplastin time.

RESULTS

The proportions of patients with negative baseline but positive postbaseline anti-APC antibodies were 1.5% (27/1855) and 1.6% (24/1493) in the DAA and placebo cohorts, respectively (P = 0.72 for the difference). Of the 27 DAA and 24 placebo patients with positive anti-APC antibodies, all but one (DAA) were alive at day 28, and all but seven (four DAA and three placebo) were alive at hospital discharge, including eight (five DAA and three placebo) patients who tested positive for anti-APC neutralizing antibodies. Two of the 51 patients who tested positive for the development of anti-APC antibodies experienced a thrombotic event (one DAA, one placebo). In ADDRESS, no anti-APC antibody was detected in the six DAA-treated patients who had received a previous course of DAA therapy.

CONCLUSIONS

The proportion of patients with anti-APC antibodies was low and was similar between DAA-treated and placebo-treated patients. No relationship between anti-APC antibody development and adverse reactions was observed. There was no evidence that the anti-APC antibodies detected represented a specific immune response to DAA therapy.

Treatment effects of drotrecogin alfa (activated) in patients with severe sepsis with or without overt disseminated intravascular coagulation

Disseminated intravascular coagulation (DIC) is a serious condition associated with sepsis. Clinical management of DIC is hampered by lack of clear diagnostic criteria. The International Society on Thrombosis and Haemostasis (ISTH) has proposed a diagnostic scoring algorithm for overt DIC based on routine laboratory tests. The objective was to assess a modified version of the ISTH scoring system and determine the effect of drotrecogin alfa (activated) (DrotAA, recombinant human activated protein C) on patients with DIC. The large database from the PROWESS clinical trial in severe sepsis was retrospectively used to assess a modified ISTH scoring system. Baseline characteristics and treatment effects of DrotAA were evaluated. At baseline, 29% (454/1568) of patients had overt DIC. Overt DIC was a strong predictor of mortality, independent of APACHE II score and age. Placebo-treated patients with overt DIC had higher mortality than patients without (43 vs. 27%). DrotAA-treated patients with overt DIC had a trend towards greater relative risk reduction in mortality than patients without (29 vs. 18%, P = 0.261) but both groups had greater relative risk reduction than placebo-treated patients. Serious bleeding rates during DrotAA infusion in patients with and without overt DIC were slightly increased (P = 0.498), compared with placebo, while clinically overt thrombotic events during the 28-day period were slightly reduced (P = 0.144). Modified ISTH overt DIC scoring may be useful as an independent assessment for identifying severe sepsis patients at high risk of death with a favorable risk/benefit profile for DrotAA treatment. Patients without overt DIC also received significant treatment benefit.

Safety and dose relationship of recombinant human activated protein C for coagulopathy in severe sepsis

OBJECTIVES

To assess the safety and effect on coagulopathy of a range of doses of recombinant human activated protein C (rhAPC). To determine an effective dose and duration of rhAPC for use in future clinical trials.

DESIGN

Double-blind, randomized, placebo-controlled, multicenter, dose-ranging (sequential), phase II clinical trial.

SETTING

Forty community or academic medical institutions in United States and Canada.

PATIENTS

One hundred thirty-one adult patients with severe sepsis.

INTERVENTIONS

Intravenous infusion of rhAPC (12, 18, 24, or 30 microg/kg/hr) or placebo for 48 or 96 hrs.

MEASUREMENTS AND MAIN RESULTS

No significant differences in incidence of serious bleeding events (4% rhAPC, 5% placebo, p >.999) or incidence of serious adverse events (39% rhAPC, 46% placebo, p = 0.422) between rhAPC- and placebo-treated patients were observed. One of 53 rhAPC-treated patients with suitable immunogenicity samples had a low level, transient, non-neutralizing anti-APC antibody response not associated with any clinical adverse event. Significant dose-dependent decreases in both D-dimer (p <0.001) and end of infusion interleukin 6 levels (p =.021) were demonstrated. No statistically significant effects on fibrinogen or platelet counts were observed. A nonstatistically significant 15% relative risk reduction in 28-day all-cause mortality was observed between rhAPC- and placebo-treated patients.

CONCLUSIONS

rhAPC was safe and well-tolerated and demonstrated a dose-dependent reduction in D-dimer and interleukin 6 levels relative to placebo. The dose of 24 microg/kg/hr for 96 hrs was selected for use in future clinical studies.

Low levels of protein C are associated with poor outcome in severe sepsis

STUDY OBJECTIVE

To investigate whether protein C levels predict 30-day mortality rate, shock status, duration of ICU stay, and ventilator dependence in patients with sepsis.

DESIGN

Retrospective analysis of a subset of a previously published, prospective, randomized, double-blind, placebo-controlled trial ("Effects of Ibuprofen on the Physiology and Survival of Patients With Sepsis" [ISS]).

SETTING

A multicenter study performed in the United States and Canada (seven sites).

PATIENTS

Seventy hospitalized patients with acute severe sepsis and failure in one or more organs at entry into the ISS trial.

MEASUREMENTS AND MAIN RESULTS

Blood samples were obtained from all patients at baseline and at 20, 44, 72, and 120 h after the initiation of study drug (ibuprofen or placebo) infusion. Data obtained at these times included platelet count, prothrombin time, and partial thromboplastin time. The results described in this article are based on a subset of the total ISS population for whom additional coagulation assays were performed on the blood samples obtained at baseline and 44 h. These assays included protein C antigen, D-dimer, and fibrinogen levels. A total of 63 of the 70 patients (90%) studied in this report had acquired protein C deficiency at entry to the ISS trial (baseline). The presence and severity of acquired protein C deficiency were associated with poor clinical outcome, including lower survival rate, higher incidence of shock, and fewer ICU-free and ventilator-free days.

CONCLUSIONS

Acquired protein C deficiency may be useful in predicting clinical outcome in patients with sepsis. Clinical studies are warranted to determine whether the replacement of protein C in sepsis patients may improve outcome.

Activated protein C versus protein C in severe sepsis

OBJECTIVE

To delineate critical differences between activated protein C (APC) and its precursor, protein C, with regard to plasma levels in health and in severe sepsis, and to discuss the implications of these differences as they relate to treatment strategies in patients with severe sepsis. DATA SOURCE/STUDY SELECTION: Published literature including abstracts, manuscripts, and review articles reporting studies in both experimental animal models and humans that provide an understanding of the relationship and the critical differences between circulating levels of APC and protein C.

DATA EXTRACTION AND SYNTHESIS

The protein C pathway represents one of the major regulatory systems of hemostasis, exhibiting antithrombotic, profibrinolytic and anti-inflammatory properties. This pathway also plays a critical role in the pathophysiology of severe sepsis. Central to this pathway is the vitamin K-dependent serine protease, APC, and its precursor, protein C. The conversion of protein C to APC is dependent on the complex of thrombin and thrombomodulin, an integral endothelial surface receptor. The conversion of protein C to APC is further augmented by another endothelial surface protein, the endothelial protein C receptor. There are limited published data on APC levels in health and disease, probably due to the complexity of the assay methodology for measuring APC and the absence of commercially available diagnostic kits. In animals and humans with normal functioning endothelium, circulating levels of APC (1-3 ng/mL) are positively correlated with protein C (4000-5000 ng/mL) concentration and the amount of thrombin generated. In patients with severe sepsis, there is a generalized endothelial dysfunction, contributing to multiple organ failure with increased morbidity and mortality. Persistently low protein C levels are related to poor prognosis. Key to understanding the treatment strategy with APC or protein C is knowledge of the functional status of the endothelium and, specifically, whether the microvasculature in patients with severe sepsis can support the conversion of protein C to APC. To date, only APC (drotrecogin alfa [activated]) has been shown to reduce mortality in severe sepsis in a large, phase 3, placebo-controlled, double-blind international trial. In contrast, no data, other than open-label case studies, are available for evaluation of the effects of protein C in the treatment of severe sepsis.

CONCLUSION

The limited data available indicate that lower levels of protein C in sepsis occur in the absence of appreciable conversion to APC. These observations indicate that treatment with APC may be more efficacious than protein C in severe sepsis, where generalized endothelial dysfunction may impair conversion of protein C to APC. Additional research is required to confirm these observations.

Protein C levels as a prognostic indicator of outcome in sepsis and related diseases

OBJECTIVE

To consider the appropriateness of protein C levels as a prognostic indicator for sepsis and related diseases.

DATA SOURCES/STUDY SELECTION

Published research and review articles related to protein C deficiency in patients with sepsis and related diseases.

DATA EXTRACTION AND SYNTHESIS

All applicable data were extracted, and relevant literature was cited to support factual statements in the text. The protein C pathway represents one of the major regulatory systems of hemostasis, exhibiting antithrombotic, profibrinolytic, and anti-inflammatory properties. Numerous studies have shown that acquired protein C deficiency is prevalent in the majority of septic patients (>85%) and is associated with increased morbidity and mortality in patients with severe sepsis and septic shock. This deficiency in protein C is not simply a transient marker for sepsis, but parallels the progress of the disease. In addition, protein C deficiency occurs in the presence of a wide range of pathogens and develops early in the disease process.

CONCLUSIONS

A review of the relevant literature suggests that protein C levels may serve as a useful prognostic indicator of outcome in sepsis and related diseases.

Isolation and characterization of mouse coagulation factor X -- biophysical and enzymological properties

Mouse factor X was highly purified from plasma using barium ion precipitation and chromatography on anion-exchange and heparin-agarose affinity chromatography columns. Intact and reduced patterns of mouse factor X in SDS-PAGE were similar to those of human factor X. The specific absorption E 1%/1 cm at 280 nm of mouse factor X was found to be 11.2. Content of carbohydrate moieties of mouse factor X, determined to be 10% by weight, differs both quantitatively and quantitatively from that of human factor X, while the gamma-carboxyglutamic acid (Gla) and beta-hydroxy-aspartic acid (beta-OH-Asp) content were essentially the same as for human factor X. The amino-terminal amino acid sequences of the light and heavy chains of mouse factor X separated by SDS-PAGE were ANSFF--FKK and SVALXTSDSE, respectively. Underlined residues are non-identical with those of human factor X. Clotting time-based assays using human factor X-deficient plasma as substrate exhibited the following apparent extents of activation of factor X in mouse plasma, using human plasma as the standard: 195% (intrinsic); 200% (extrinsic); and 190% (RVV-X). Using the purified proteins in the same assay systems, the following apparent activation of mouse factor X was demonstrated, compared with human factorX: 195% (intrinsic); 27% (extrinsic); and 41% (RVV-X). These activity profiles suggest that the human extrinsic coagulation pathway functions less efficiently than the corresponding mouse pathway in the activation of mouse factor X. Furthermore, mouse brain thromboplastin satisfactorily replaced rabbit brain thromboplastin in extrinsic activation of factor X in mouse plasma, but not of human plasma or purified mouse or human factor X, in line with studies by others suggesting that human factor VIIa poorly activates factor X in the presence of mouse tissue factor. While fully RVV-X-activated mouse factor X activated human prothrombin at a rate equal to about 117% of that for human factor X, it hydrolyzed the synthetic substrate, S-2222, at a rate of only about 18% of that for human factor X. These results are expected to be useful in making the mouse suitable for study of the mammalian blood coagulation pathways.

Review of conformation-specific affinity purification methods for plasma vitamin K-dependent proteins

There are seven known vitamin K-dependent proteins in blood. These proteins require calcium ion for expressing their full biological activities. Calcium ion also induces conformational changes in this class of proteins. Taking advantage of the ligand induced conformational changes, a number of unique approaches of affinity chromatography have been developed. These methodologies have been very useful tools for both the purification and for understanding the structure-function relationships of this class of proteins. One method is the use of metal ion dependent immunoaffinity chromatography. The antigen can be dissociated from the antibodies with either the removal or addition of calcium ion under physiological conditions. The other method is pseudoaffinity chromatography. This method uses conventional ion-exchange or hydrophobic resin and manipulates the mobilities of the proteins on these resins by the presence or absence of calcium ions. Researchers working with other calcium binding proteins or other proteins that are known to undergo ligand induced conformational changes may benefit from the experience of these unique conformation-specific affinity chromatography approaches.

High mobility group protein, HMG-1, contains insignificant glycosyl modification

High mobility group protein-1 (HMG-1) is a ubiquitous, highly conserved, and abundant nuclear protein. Recent findings suggest that HMG-1 may serve as a DNA chaperone protein and play a role in the regulation of transcription. There is a mounting interest in elucidating the mechanism by which HMG-1 protein takes part in these activities. HMG-1 has been reported to undergo an extensive array of posttranslational modifications, including glycosylation. We extend the earlier findings on the glycosylation of HMG-1 by quantitating the amount of carbohydrate on HMG-1 from calf thymus and chicken erythrocytes isolated by 2 different purification procedures. In addition, 2 different developmental stages (embryonic and adult) were examined in the chicken erythrocytes. The glycosyl composition was quantitated using the Dionex HPAE-PAD II system. Furthermore, the presence of O-linked GlcNAc on HMG-1 was determined by the enzymatic incorporation of 3H-galactose into HMG-1 protein. Contrary to earlier reports, less than 0.5 mol of total monosaccharides (Fuc, Man, GalNH2, GlcNH2, Gal) were detected per mole of HMG-1 protein, regardless of the source of the protein or the method of isolation. In addition, less than 0.002 mol of O-linked GlcNAc per mole of HMG-1 protein was detected. Thus, insignificant amount of glycosylation was found on HMG-1 protein. Because O-linked GlcNAc modification of proteins is believed to be a reversible posttranslational event, more definitive studies will need to be conducted before ruling out that the function of HMG-1 protein is not regulated by glycosylation.

Characterization and cilofungin inhibition of solubilized Aspergillus fumigatus (1,3)-beta-D-glucan synthase

(1,3)-beta-D-Glucan synthase, a major cell wall synthesis enzyme, is the target of antifungal drugs of the lipopeptide class. Aspergillus fumigatus (1,3)-beta-D-glucan synthase was prepared and its activity was measured by incorporation of [14C]glucose from UDP-[U-14C]glucose into an insoluble polymer in the presence of alpha-amylase. Solubilization of the (1,3)-beta-D-glucan synthase was attempted with several detergents, and the maximum percent solubilization was obtained with a polyoxyethylene ether detergent, W-1. Up to 70% of enzyme activity and 50% of total protein were recovered when 1-mg/ml membrane preparations were extracted with 0.045% W-1 at 4 degrees C overnight. Confirmation of the presence of a (1,3)-beta-D-glucose polymer synthesized by this glucan synthase was done by three methods. The first was enzymatic end product degradation by alpha-amylase (no degradation) and beta-glucanase (85 to 95% degradation). The second was gas chromatography-mass spectroscopy analysis of the partially methylated alditol acetate derivatives prepared from total carbohydrate polymers present in the sample. This method identified the presence of (1,3)- and (1,2)-glucosidic linkages. The third was high-performance anion exchange chromatography of radioactive oligosaccharides. This method allowed differentiation of the newly synthesized, radioactive polymers from the contaminating carbohydrates already present in the preparation. The results showed that the polymer synthesized comprised oligosaccharides consistent with beta-(1,3)-linked sugars. Maximal inhibition of the (1,3)-beta-D-glucan synthase by the lipopeptide antifungal agent cilofungin was 80%. Dose-response experiments with this inhibitor showed that the solubilized enzyme was maximally inhibited at a cilofungin concentration of 1.25 microgram/ml and showed <5% inhibition at 0.02 microgram/ml. The apparent K(m) (K(m app)) for the solubilized glucan synthase was 400 +/- 80 microM, and the apparent K(i) (K(i app)) for cilofungin was 0.19 +/- 0.03 microM. Inhibition of A.fumigatus (1,3)-beta-D-glucan synthase with cilofungin was noncompetitive, as it was for the Candida albicans (1,3)-beta-D-glucan synthase.

Human protein C inhibits selectin-mediated cell adhesion: role of unique fucosylated oligosaccharide

The human anticoagulant factor, Protein C, is a plasma glycoprotein that has reported anti-ischaemic and anti-inflammatory properties. To explore potential mechanisms for these reported activities, we examined the effect of Protein C on the process of cell adhesion to vascular endothelial cells, which plays a critical role during inflammatory responses. We show that both human plasma-derived and human cell-produced recombinant Protein C inhibit E-selectin-mediated cell adhesion. This effect was not mediated through the serine protease activity of Protein C, but through its carbohydrates. Using oligosaccharides isolated from human cell-produced Protein C, we have defined a polylactosamine structural determinant that inhibits adhesion. This uncharged determinant appears to be a more potent ligand for E-selectin than the sialylated Lewis X antigen. Our data suggest a potential mechanism for the reported anti-inflammatory effects of Protein C and describe a new ligand for selectin-mediated adhesion.

Novel Asn-linked oligosaccharides terminating in GalNAc beta (1-->4)[Fuc alpha (1-->3)]GlcNAc beta (1-->.) are present in recombinant human protein C expressed in human kidney 293 cells

Recombinant human Protein C (rHPC), expressed in human kidney 293 cells, has a higher anticoagulant activity than plasma HPC, while its in vivo circulatory half-life is essentially unaltered compared to that of the natural protein. In seeking to elucidate the molecular basis for the improved efficacy of the recombinant antithrombotic drug, we focused on the carbohydrate moiety of rHPC. Protein C is a heavily post-translationally modified serine protease with four N-glycosylation sites. Glycosyl composition analysis of rHPC revealed a 5-fold higher fucose content and a 2-fold lower sialic acid content compared to plasma HPC. In addition, we found that rHPC contains N-acetylgalactosamine (2.6 mol GalNAc/mol rHPC) in its Asn-linked oligosaccharides, while plasma HPC is devoid of GalNAc. The Asn-linked oligosaccharides of rHPC were released by N-glycanase and separated into 25 fractions by high-pH anion-exchange chromatography. The most abundant oligosaccharides were structurally characterized by glycosyl composition and linkage analysis, in conjunction with 1H-NMR spectroscopy at 600 MHz. The structure of the major neutral oligosaccharide in rHPC was determined to be: [formula: see text] Two representatives of the sialylated oligosaccharides in rHPC are: [formula: see text] and [formula: see text] Thus, many of the Asn-linked oligosaccharides in rHPC were found to terminate in GalNAc beta (1-->4)GlcNAc beta (1-->.), in NeuAc alpha (2-->6)GalNAc beta (1-->4)GlcNAc beta (1-->.), and/or in GalNAc beta (1-->4)[Fuc alpha (1-->3)]GlcNAc beta (1-->.). Since the latter trisaccharide was first [Yan, S.B., Chao, B.Y. and Van Halbeek,H. (1992) J. Cell. Biochem., 16D, 151] observed in the Asn-linked oligosaccharides of rHPC derived from human kidney 293 cells, we propose to label the GalNAc beta-(1-->4)[Fuc alpha (1-->3)]GlcNAc beta (1-->.) terminal trisaccharide the PC-293 determinant. The PC-293-containing oligosaccharides may contribute to the higher anticoagulant activity of rHPC as compared to plasma HPC.

Design and implementation of a particle concentration fluorescence method for the detection of HIV-1 protease inhibitors

A critical step in the replicative cycle of the human immunodeficiency virus HIV-1 involves the proteolytic processing of the polyprotein products Prgag and Prgag-pol that are encoded by the gag and pol genes in the viral genome. Inhibitors of this processing step have the potential to be important therapeutic agents in the management of acquired immunodeficiency syndrome. Current assays for inhibitors of HIV-1 protease are slow, cumbersome, or susceptible to interference by test compounds. An approach to the generation of a rapid, sensitive assay for HIV-1 protease inhibitors that is devoid of interference problems is to use a capture system which allows for isolation of the products from the reaction mixture prior to signal quantitation. In this paper, we describe a novel method for the detection of HIV-1 protease inhibitors utilizing the concept of particle concentration fluorescence. Our approach involves the use of the HIV-1 protease peptide substrate Ser-Gln-Asn-Tyr-Pro-Ile-Val which has been modified to contain a biotin moiety on one side and a fluorescein reporter molecule on the other side of the scissile Tyr-Pro bond. This substrate is efficiently cleaved by the HIV-1 protease and the reaction can be readily quantitated. Known inhibitors of the protease were readily detected using this new assay. In addition, this approach is compatible with existing instrumentation in use for broad screening and is highly sensitive, accurate, and reproducible.

Viral transformation increases vitamin K-dependent gamma-carboxylation of glutamate

Mammalian cells contain a microsomal vitamin K-dependent carboxylase activity which catalyzes the gamma-carboxylation of glutamate. While most cells have a limited ability to fully gamma-carboxylate proteins, it has been suggested that the ability of transformed cells to perform this complex post-translational modification may play a role in tumor biology. In this study, we examined the effect of transformation by adenovirus oncogenes on the ability of cells to efficiently gamma-carboxylate a vitamin K-dependent protein. Several morphologically transformed BHK-21 cell lines (BHK-Ad) were isolated following the chromosomal integration of the viral oncogenes E1A/E1B from human adenovirus type 12 (Ad12). The lines were capable of growing in soft agar and low serum and produced functional E1A as determined by promoter activation studies. Using a vector for the expression of the vitamin K-dependent recombinant human protein C (HPC), a regulator of the clotting cascade, Ad-transformed and nontransformed lines secreting rHPC were generated. The rHPC from the transformed and nontransformed cell lines displayed identical serine protease activities, and there were no apparent differences in the proteolytic processing of the proteins, although a minor difference in the proportion of each HPC glycoform was observed. However, the functional anticoagulant activity, which depends on the gamma-carboxyglutamic acid (Gla) content, was approximately 70% higher in the Ad-transformed lines. Approximately 90% of the rHPC from the Ad-transformed lines exhibited a calcium-dependent (high Gla) elution profile on anion-exchange resin, compared to only 15 to 26% from the nontransformed cell clones. By analyzing endogenous microsomal carboxylase, we determined that enzyme activity increased approximately 50% following transformation. Overall, our data demonstrate that transformation can increase the potential of a cell to efficiently gamma-carboxylate a protein and lend support to the suggested involvement of this post-translational modification in tumor cell function. Further, our results demonstrate a potential means of altering cells to enable full modification of vitamin K-dependent factors for structure/function studies and potentially for therapeutic use.

Gamma-carboxylated isoforms of recombinant human protein S with different biologic properties

Human protein S (HPS), a regulator of hemostasis, is a vitamin K-dependent plasma protein with potential clinical utility. We have obtained high-level expression of the cDNA for HPS in two mammalian cell lines. Both cell lines secreted single chain recombinant HPS (rHPS) in serum-free medium as determined by Western blot analysis. The ability of the rHPS from both cell lines to act as a cofactor for human protein C (HPC) was determined; the rHPS secreted from the human 293 cell line had an activity six times that of the rHPS from the AV12-664 Syrian hamster cell line. Furthermore, the relative specific cofactor activity of rHPS from the 293 cell line was actually 2.5-fold higher than that of single-chain human plasma-derived HPS. Essentially all of the rHPS secreted from the 293 cell line exhibited a calcium-dependent elution profile on anion exchange chromatography, whereas only 25% to 35% of the hamster cell-derived rHPS exhibited this profile. However, the calcium-eluted rHPS from the AV12 cell line had a high specific cofactor activity, equivalent to that of the 293-derived rHPS. A NaCl-elutable rHPS fraction (calcium nondependent) was isolated from the recombinant AV12-664 cell line, further purified, and found to have reduced activity, only 40% that of the calcium-dependent rHPS. The only observable difference in the calcium-dependent and nondependent rHPS molecules was in the content of gamma-carboxyglutamic acid (Gla); the calcium-dependent material contained approximately 10 mol Gla/mol protein whereas the calcium-nondependent material contained only approximately 8 mol Gla/mol of protein. In addition, the calcium-nondependent rHPS had reduced ability to interact with phospholipid vesicles as evidenced by an eightfold increase in the apparent kd. Our data demonstrate the isolation of rHPS with high specific activity, and show that a reduction in as few as two Gla residues dramatically decreases its functional cofactor activity for HPC, due to a reduction in ability to interact with the phospholipid bilayer.

Recombinant human protein C derivatives: altered response to calcium resulting in enhanced activation by thrombin

Calcium plays a dual role in the activation of protein C: it inhibits protein C activation by alpha-thrombin, whereas it is required for protein C activation by the thrombomodulin-thrombin complex. Available information suggests that these calcium effects are mediated through calcium induced structural changes in protein C. In this paper, we demonstrate that substitution of Asp167 (located in the activation peptide of human protein C, occupying position P3 relative to the peptide bond Arg169-Leu170 which is susceptible to hydrolysis by thrombin) by either Gly or Phe results in protein C derivatives which are characterized by an altered response to calcium. At 3 mM calcium, alpha-thrombin activated the derivatives 5- to 8-fold faster compared with the wild-type, an effect which was shown to be caused by a decreased inhibitory effect of calcium on the reaction. These same single amino acid substitutions enhanced the affinity of the thrombomodulin-thrombin complex for the substrate at 3 mM calcium 3-(Gly-substitution) to 6-(Phe-substitution) fold, either without influencing kcat (Gly-substitution) or with a 2.5-fold decrease of kcat. For both derivatives, the calcium concentrations resulting in half maximal inhibition of activation by alpha-thrombin and in half maximal stimulation of activation by the thrombomodulin-thrombin complex increased from 0.3 mM to 0.6 mM. It is concluded that Asp167 is involved in the calcium induced inhibition of protein C activation by thrombin. Moreover, our studies demonstrate that it is feasible to enhance the efficiency of enzymatic reactions by introducing point mutations in the substrate.

Amplification of multicistronic plasmids in the human 293 cell line and secretion of correctly processed recombinant human protein C

We have constructed multicistronic vectors containing the cDNAs for murine dihydrofolate reductase (DHFR), hygromycin phosphotransferase (HyPR), and human protein C (HPC), an antithrombotic factor. Using a sequential selection protocol with hygromycin (Hy) and methotrexate (MTX), we demonstrate the selective amplification of the murine dhfr cDNA in the adenovirus-transformed human kidney cell line 293, and the coamplification of the cDNA for HPC. Such recombinant 293 cell lines secreted HPC at levels as high as 25 micrograms/10(6) cells/day. In addition, we found that the complex vitamin K-dependent posttranslational modification of gamma-carboxylation of glutamate was not limiting at these high secretion levels, although the proteolytic processing of the protein was slightly reduced. Further, the HPC secreted from the gene-amplified cell lines had full anticoagulant activity when compared to plasma-derived HPC.

Direct expression of recombinant activated human protein C, a serine protease

Human protein C, like other serine proteases, is normally secreted as an inactive zymogen. It is converted to its active form extracellularly by limited proteolysis with the thrombin-thrombomodulin complex. This activation results from the removal of a 12-residue activation peptide from the NH2 terminus of the heavy (COOH-terminal) chain. We report here a successful strategy for the activation of human protein C during post-translational cellular processing, resulting in the secretion of activated protein C from transfected mammalian cells. Deletion of the nucleotides encoding the activation peptide resulted in the expression of a protease with less than 5% of the expected activity. However, the replacement of the activation peptide with an 8-residue sequence (Pro-Arg-Pro-Ser-Arg-Lys-Arg-Arg) involved in the proteolytic processing of the human insulin receptor precursor resulted in the direct expression of fully activated protein C. The mutant protein was shown to be correctly processed by NH2-terminal sequence analysis. This strategy for successful expression of an activated form of protein C may apply to the expression of active forms of other proteases which are naturally expressed as zymogens.

Neoglycoproteins: in vitro introduction of glycosyl units at glutamines in beta-casein using transglutaminase

Exploring different methods for preparing neoglycoproteins with a specific number of oligosaccharides in specific positions, we have used guinea pig liver transglutaminase to incorporate glycosyl units into glutamine residues in beta-casein. In order to prevent epsilon-(gamma-glutamyl)lysine cross-link formation, the lysine residues of beta-casein were first blocked either by amidination with ethyl acetimidate or by acylation with succinic anhydride. The glycosyl donor substrates prepared for this work were maltotriose reductively aminated with cadaverine, N-(Glc-Glc-glucitol-1)-cadaverine, and an asparaginyl nonasaccharide from ovalbumin modified with a 6-aminohexanoyl group at the alpha-amino group. The transglutaminase-catalyzed incorporation of these two donors into the beta-casein derivatives was monitored in comparison to the incorporation of the commonly used transglutaminase substrate dansylcadaverine under conditions of optimal incorporation (multiple additions of enzyme, large excess of donor, and long incubation time). For both dansylcadaverine and Glc-Glc-Glc(OH)-cadaverine, 5 and 8 mol of donor were incorporated per mol of amidinated and succinylated beta-casein, respectively. Competition experiments showed that the two donor substrates are incorporated into the same glutamine sites. Partial sequencing of the glycosylated beta-casein permitted the identification of glutamine residues 56, 79, 167, 175, and 194 as the primary sites of incorporation in amidinated casein with residues 54 and 182 as possible sites for partial glycosylation. The results are consistent with a specific glycosylation of only selected glutamines in this transglutaminase-catalyzed process.(ABSTRACT TRUNCATED AT 250 WORDS)

Polyethylene glycol interferes with protein molecular weight determinations by gel filtration

Gel filtration studies on Sephadex G-75 demonstrate markedly increased elution volumes for proteins chromatographed with polyethylene glycol. As little as 5% (w/v) polyethylene glycol in the applied protein sample can reduce apparent molecular weight estimates by gel filtration as much as 55%. Furthermore, gel filtration columns equilibrated with polyethylene glycol are not size-separating columns. Consequently, caution must be exercised when performing and interpreting gel filtration studies of proteins previously treated or precipitated with polyethylene glycol.