Full-length cDNA cloning and protein three-dimensional structure modeling of porcine prothrombin

Unique properties of prothrombin in the bullhead shark Heterodontus japonicus: the first report of purification and characterization of a blood coagulation factor in Chondrichthyes

Prothrombin is a serine protease precursor of the blood coagulation system. In this study, the primary structure of prothrombin of a cartilaginous fish, bullhead shark (Heterodontus japonicus), was determined using RNA-Seq and the protein was purified from the blood plasma. Bullhead shark prothrombin was found to be comprised of four domains, as in the case of reported mammalian homologues. Two arginine residues that should be cleaved by activated factor X were found in the amino acid sequence of the shark prothrombin, but only one of the two cleavage sites for thrombin or meizothrombin was conserved. The apparent molecular mass of the shark prothrombin on SDS-PAGE was 110 kDa, whereas that of its amino acid sequence was 65 kDa. Potential N-glycosylation sites were found at 79th, 108th, 121st, 179th, 199th, 507th, and 527th asparagine residues in the shark prothrombin, and treatment with N-glycosidase reduced the molecular mass to 65 kDa. This indicates that, in contrast to human prothrombin, which has only 7-kDa N-glycans, the prothrombin of the shark is highly N-glycosylated. This study is the first to report on the purification and characterization of blood coagulation factors in a cartilaginous fish.

Functional expression of the human coagulation factor IX using heterologous signal peptide and propeptide sequences in mammalian cell line

OBJECTIVE

To study the functions of pre-pro leader peptides of the human and porcine prothrombins on the human FIX (hFIX) expression.

RESULTS

In silico analysis predicted higher secretion efficiencies for the prothrombins-derived signal peptides, in comparison with the native hFIX signal peptide. Replacements of the hFIX pre-pro sequence with those of the two prothrombins, led to increased levels of transcription of the chimeric transgenes, as compared to the native clone. This was in consistent with the lower minimum free energies, calculated for the recombinant transcripts, based on their secondary structures. Evaluation of secretion efficiency revealed that the highest and lowest FIX secretions belong to signal peptides derived from porcine' prothrombin and hFIX, respectively. Coagulation activities of the FIX expressed from chimeric variants could be increased up to tenfold, relative to the native clone.

CONCLUSION

The feasibility of a leader-peptide replacement for the improvement of both transcription and post-transcriptional processes is described that can be relevant for production the vitamin-K dependent proteins.

Research on PEGylation of porcine prothrombin for improving biostability and reducing animal immunogenicity

Prothrombin is a vitamin K-dependent serine protease and plays pivotal roles in both procoagulant and anticoagulant pathway of hemostasis. In this study, prothrombin purified from porcine plasma was modified through PEGylation at N-terminal residue using 40 kDa PEG-phenyl-isothiocyanate (PIT-PEG40K). The monoPEGylated prothrombin enhanced biostability and remarkably prolonged circulating half-life in mice as compared with that of the nonmodified prothrombin. Moreover, the immunogenicity of PEGylated prothrombin in mice is significantly decreased compared to nonmodified prothrombin. These studies demonstrated the feasibility of PEGylating prothrombin as a promising way for the development of new prothrombin drugs.

Relative purity of different bovine thrombin preparations

The aim of this study was to compare the relative purity of bovine crude thrombin and its purified forms, namely, thrombin 4A and thrombin 4B (the products of King Pharma, Middleton, Wisconsin) by virtue of the detection of bovine prothrombin-related antigens in these preparations. Bovine prothrombin was administered intravenously to 3 individual rabbits on days 0, 21, 42, 91, 123, and 151 using standard immunologic method. Blood was drawn from each rabbit on days 30, 50, 105, 137, and 165, and the pooled antisera from 3 rabbits were purified to isolate immunoglobulin G (IgG) using protein G affinity columns. Using Western blotting method, serially diluted bovine crude thrombin, thrombin 4A, and 4B preparations were probed using the prothrombin IgGs obtained from each time point to explore prothrombin-related antigens in these preparations. The results revealed that compared with the prothrombin IgG collected on day 30, the IgGs collected on days 50 to 165 showed a time-dependent increase in their ability to detect the prothrombin-related antigens in 3 bovine thrombin preparations studied. The lowest amount of crude thrombin, thrombin 4A, and 4B preparations that prothrombin IgG could detect was 0.125, 10, and 20 U, respectively. The rank order of the number of immunoreactive bands detectable in 3 bovine thrombin preparations probed by the prothrombin IgGs collected from any given time point was always the same: crude thrombin > thrombin 4A > thrombin 4B. The results indicate that thrombin 4B preparation contains the least amount of antigens detectable by prothrombin IgG, suggesting that relatively thrombin 4B represents the most purified thrombin preparation among the 3 thrombin preparations studied.

Poly(methyl methacrylate) microchip affinity capillary gel electrophoresis of aptamer-protein complexes for the analysis of thrombin in plasma

Thrombin generation in blood serves as an important marker for various hemostasis-related diseases and conditions. Analytical techniques currently utilized for determining the thrombin potential of patients rely primarily on the enzymatic activity of thrombin. Microfluidic-based ACE using fluorescently labeled aptamers as affinity probes could provide a simple and efficient technique for the real-time analysis of thrombin levels in plasma. In this study, aptamers were used for the analysis of thrombin by affinity microchip CGE. The CGE used a poly(methyl methacrylate) (PMMA) microfluidic device for the sorting of the affinity complexes with a linear polyacrylamide (LPA) serving as the sieving matrix. Due to the fact that the assay was run under nonequilibrium electrophoresis conditions, the presence of the sieving gel was found to stabilize the affinity complex, providing improved electrophoretic performance compared to free-solution electrophoresis. Two fluorescently labeled aptamer affinity probes, HD1 and HD22, which bind to exosites I and II, respectively, of thrombin were investigated. With an electric field strength of 300 V/cm, two well-resolved peaks corresponding to free aptamer and the thrombin-aptamer complex were obtained in less than 1 min of separation time with a run-to-run and chip-to-chip reproducibility (RSD) of migration times <10% using both aptamers. HD22 affinity assays of thrombin produced baseline-resolved peaks with favorable efficiency due to its higher binding affinity, whereas HD1 assays showed poorer resolution of the free aptamer and complex peaks. HD22 was used in determining the level of thrombin in human plasma. Assays were performed directly on plasma that was diluted to 10% v/v. Thrombin was successfully analyzed by microchip CGE at a concentration level of 543.5 nM for the human plasma sample.

Cloning, sequencing, and analysis of the full-length CDNA of rhesus monkey factor IX

OBJECTIVE

Coagulation factor IX (FIX) is a vitamin K-dependent serine protease, which plays a key role in the coagulation cascade. The rhesus monkey may be an indispensable substitute for humans in research of pig-to-human xenotransplantation, due to its close relationship. But the coagulation function concordance between rhesus monkey and human is unknown. In this study, we cloned the full-length cDNA of rhesus monkey FIX (rFIX) to investigate the genomic backgrounds of the coagulation systems.

METHOD

We cloned the full-length cDNA from the cDNA library of rhesus monkey liver tissue. Polymerase chain reaction was used to screen the positive clones. Based on a partial sequence obtained by cDNA library screening and a homologous sequence from the database, we designed a second pair of primers to obtain the full sequence. For further analysis of rFIX, we used several online ExPASy Proteomic tools.

RESULT

We obtained the full-length cDNA of rFIX, which has 2668 nucleotides, predicting an open reading frame of 1383 nucleotides corresponding to 461 amino acids. The deduced protein sequence indicated functional domains of signal peptide, Gla, two epidermal growth factor, and trypsin-like serine protease, which were consisted with those of human FIX (hFIX). Sequence alignments showed that rFIX is highly homologous to hFIX with nucleotide identity of 96% and amino acid identity of 97%.

CONCLUSION

We have report herein the full-length cDNA of rFIX. The high homology between rhesus monkey and human coagulation factor ensure the reliability and feasibility of rhesus monkey as a recipient in studies on coagulation disorders in xenotransplantation.

Pig thrombomodulin binds human thrombin but is a poor cofactor for activation of human protein C and TAFI

Incompatibility between pig thrombomodulin (TM) and primate thrombin is thought to be an important factor in the development of microvascular thrombosis in rejecting pig-to-primate xenografts. To examine this interaction at the molecular level, we cloned pig TM and measured its ability to bind human thrombin and act as a cofactor for the activation of human protein C and TAFI. The 579-residue pig TM protein showed approximately 69% sequence identity to human TM. Within the EGF domains necessary for binding of thrombin (EGF56), protein C (EGF4) and TAFI (EGF3), all of the amino acids previously identified as critical for the function of human TM, with the exception of Glu-408 in EGF5, were conserved in pig TM. Comparison of transfected cells expressing pig or human TM demonstrated that both proteins bound human thrombin and inhibited its procoagulant activity. However, pig TM was a poor cofactor for the activation of human protein C and TAFI, with domain swapping showing that EGF5 was the most important determinant of compatibility. Thus, while pig TM may be capable of binding thrombin generated in the vicinity of xenograft endothelium, its failure to promote the activation of human protein C remains a significant problem.