heparin-Sepharose Affinity Chromatography Research Articles

Heparin binding triggers human VLDL remodeling by circulating lipoprotein lipase: Relevance to VLDL functionality in health and disease

Hydrolysis of VLDL triacylglycerol (TG) by lipoprotein lipase (LpL) is a major step in energy metabolism and VLDL-to-LDL maturation. Most functional LpL is anchored to the vascular endothelium, yet a small amount circulates on TG-rich lipoproteins. As circulating LpL has low catalytic activity, its role in VLDL remodeling is unclear. We use pre-heparin plasma and heparin-sepharose affinity chromatography to isolate VLDL fractions from normolipidemic, hypertriglyceridemic, or type-2 diabetic subjects. LpL is detected only in the heparin-bound fraction. Transient binding to heparin activates this VLDL-associated LpL, which hydrolyses TG, leading to gradual VLDL remodeling into IDL/LDL and HDL-size particles. The products and the timeframe of this remodeling closely resemble VLDL-to-LDL maturation in vivo. Importantly, the VLDL fraction that does not bind heparin is not remodeled. This relatively inert LpL-free VLDL is rich in TG and apoC-III, poor in apoE and apoC-II, shows impaired functionality as a substrate for the exogenous LpL or CETP, and likely has prolonged residence time in blood, which is expected to promote atherogenesis. This non-bound VLDL fraction increases in hypertriglyceridemia and in type-2 diabetes but decreases upon diabetes treatment that restores the glycemic control. In stark contrast, heparin binding by LDL increases in type-2 diabetes triggering pro-atherogenic LDL modifications. Therefore, the effects of heparin binding are associated negatively with atherogenesis for VLDL but positively for LDL. Collectively, the results reveal that binding to glycosaminoglycans initiates VLDL remodeling by circulating LpL, and suggest heparin binding as a marker of VLDL functionality and a readout for treatment of metabolic disorders.

Ancestral Sequence Reconstruction of Von Willebrand Factor Reveals Highly Conserved Structure/Function

Von Willebrand factor (VWF) is a large multimeric glycoprotein of critical importance for both primary and secondary hemostasis due to its role in platelet activation and stabilization of coagulation factor VIII (FVIII), respectively. Mutations affecting VWF synthesis, secretion, or function result in one of 6 distinct subtypes of von Willebrand disease (VWD) with mutations inhibiting FVIII binding classified as type 2N. Due to low circulating levels of plasma FVIII, type 2N patients can be misdiagnosed with hemophilia A. Because the clearance of FVIII is dominated by its association with VWF, and given recent evidence demonstrating an immuno-protective role of VWF for FVIII, understanding the molecular interaction between FVIII and VWF remains critically important for both hemophilia A and type 2N VWD therapeutic development. However, limited structural information remains a major limitation for rational design studies. Recently, ancestral sequence reconstruction (ASR) was performed to infer the sequences of FVIII predicted to have existed throughout mammalian evolution. ASR provides a platform for high-resolution mapping of sequential differences within a phylogeny while maintaining a high probability of retaining function. Sequential changes in the amino acid sequence of FVIII appears to have resulted in altered biochemical properties including biosynthesis and stability. In this study, we demonstrate that a previously characterized ancestral (An) FVIII molecule with 95% identity to human FVIII, termed An53-FVIII, exhibits a 2.5 to 5-fold increase in binding to human VWF over commercial recombinant FVIII products, suggesting a dynamic association throughout evolution. We sought to further explore the FVIII-VWF interaction through ASR of VWF and biochemical analysis.A phylogenetic tree was constructed for VWF and the ancestral amino acid sequences predicted through Bayesian inference. A compiled list of 59 extant sequences allowed accurate prediction of the sequences extending beyond the class Mammalia. Of the resulting 50, 5 An-VWF sequences representing significant branch points in primate, rodent, and ungulate evolution were selected for synthesis de novo and subsequent biochemical characterization. All sequences, including an additional human (h) VWF cDNA, were human codon optimized (co). These sequences are predicted to span 105 million years of evolution and contain 81 to 364 amino acid substitutions (Table 1). Heterologous expression in HEK293 cells demonstrated that all An-VWF sequences resulted in secreted antigen as determined by ELISA using anti-human VWF polyclonal antibodies. Furthermore, immunohistochemistry of HEK293 cells expressing An-VWF revealed the formation of pseudo Weibel-Palade bodies by all VWF proteins. Stably transected, clonal producer cell lines were generated and utilized for recombinant VWF production and purification using heparin-sepharose affinity chromatography. Consistent with our IHC studies, multimer analysis of the purified proteins revealed the presence of high molecular weight multimers equivalent to human plasma VWF. To test the functionality of An-VWF, the VWF:GPIbM assay was performed. Compared to an observed specific activity of 45 IU/mg VWF for cohVWF, An-VWF molecules displayed specific activities ranging from 6 to 94 IU/mg. These data suggest that VWF and GPIb may have co-evolved to regulate platelet adhesion and activation. Hydrodynamic injection of An63-, An88-, and An101-VWF plasmid DNA into VWF deficient mice revealed plasma VWF levels of 1.44 ± 0.48, 0.72 ± 0.16, and 2.9 μg/mL at 24 hours after administration, respectively (n = 4, 3, and 1). Additionally, endogenous mouse (m) FVIII levels in these mice were elevated to 61 ± 9, 75 ± 16, and 67% of normal levels from a basal 12.9 ± 2.4%. This data demonstrates that liver synthesized An-VWF retains FVIII association and stabilization. Molar ratios of An88-VWF:mFVIII are 6:1 compared to 14:1 and 25:1 for An63- and An101-VWF, respectively, supporting the coevolution hypothesis for VWF and FVIII. Cumulatively, this study further validates the utility of ASR for the generation of functional sequences for complex proteins with a high propensity for inactivating mutations. Further analysis of ancestral sequences may provide greater resolution of amino acid sequences responsible for biochemical properties including clearance and FVIII association. [Display omitted] DisclosuresGaucher:General Genomics: Equity Ownership.

Expression and one-step purification of active LPL contemplated by biophysical considerations

LPL is essential for intravascular lipid metabolism and is of high medical relevance. Since LPL is notoriously unstable, there is an unmet need for a robust expression system producing high quantities of active and pure recombinant human LPL (hLPL). We showed previously that bovine LPL purified from milk is unstable at body temperature (Tm is 34.8°C), but in the presence of the endothelial transporter glycosylphosphatidylinositol-anchored high density lipoprotein-binding protein 1 (GPIHBP1), LPL is stabile (Tm increases to 57.6°C). Building on this information, we now designed an expression system for hLPL using Drosophila Schneider 2 cells grown in suspension at high cell density and at an advantageous temperature of 25°C. We cotransfected Schneider 2 cells with hLPL, lipase maturation factor 1, and soluble GPIHBP1 to provide an efficient chaperoning and stabilization of LPL in all compartments during synthesis and after secretion into the conditioned medium. For LPL purification, we used heparin-Sepharose affinity chromatography, which disrupted LPL-GPIHBP1 complexes causing GPIHBP1 to elute with the flow-through of the conditioned media. This one-step purification procedure yielded high quantities of pure and active LPL (4–28 mg/l). Purification of several hLPL variants (furin cleavage-resistant mutant R297A, active-site mutant S132A, and lipid-binding-deficient mutant W390A-W393A-W394A) as well as murine LPL underscores the versatility and robustness of this protocol. Notably, we were able to produce and purify LPL containing the cognate furin cleavage site. This method provides an efficient and cost-effective approach to produce large quantities of LPL for biophysical and large-scale drug discovery studies.

Proteins and Heparin Binding Proteins of Spermatozoa and Seminal Plasma in Beetal Bucks: Purification, Characterization and Role in In vivo Fertility

Background: The proteome analysis of seminal plasma and spermatozoa is of special relevance in livestock. Heparin binding proteins (HBPs) found in the seminal plasma of several mammals are shown to bind to sperm membrane and affect a series of events that contribute to normal fertility, such as sperm capacitation, formation of the oviduct reservoir and binding to the oocyte. Profiles of HBPs from seminal plasma and sperm membranes have been associated with sperm fertility. Although, HBPs present in the SP are described in several species, but little is known about HBPs in buck. Methods: Seminal plasma (SP) and sperm extracts (SE) of 13 bucks were subjected to heparin-sepharose affinity chromatography. Sperm extract, seminal plasma and purified HBPs and Non-HBPs were fractionated by SDS-PAGE. Total 78 females (6 per buck) were mated with 13 bucks. Bucks were divided into two groups, G-I (high fertile, 83.3-100% FR) and G-II (low fertile, 50-66.7% FR). Relationship between HBPs and fertility rate was observed. Result: SDS – PAGE of SP and SE resulted in resolution of 22 (10-240 kDa) and 21 (10-270 kDa) bands, respectively. Based on fertility rate 15 and 13 kDa proteins were absent in SP of higher number of GI-compared to G-II bucks. Fourteen bands ranging from 10 – 180 kDa and 10 – 150 kDa were separated from SP-NHBP and SP-HBP. SP-HBPs of 75, 35, 30, 28, 25 and 13 kDa were present in higher (28.6%, 42.5%, 26.2%, 40.5%, 14.3% and 36.2%) number of high fertile than low fertile bucks. NHBP and HBP purified from SE resolved into 11 bands ranging from 10 – 135 kDa and 10 – 120 kDa, respectively. SE-HBP of 53 kDa, 50/45 kDa and 25 kDa were present in higher percentage of high fertile than low fertile bucks.

Simple and Efficient Purification of Recombinant Proteins Using the Heparin-Binding Affinity Tag.

Heparin, a member of the glycosaminoglycan family, is known to interact with more than 400 different types of proteins. For the past few decades, significant progress has been made to understand the molecular details involved in heparin-protein interactions. Based on the structural knowledge available from the FGF1-heparin interaction studies, we have designed a novel heparin-binding peptide (HBP) affinity tag that can be used for the simple, efficient, and cost-effective purification of recombinant proteins of interest. HBP-tagged fusion proteins can be purified by heparin Sepharose affinity chromatography using a simple sodium chloride gradient to elute the bound fusion protein. In addition, owing to the high density of positive charges on the HBP tag, recombinant target proteins are preferably expressed in their soluble forms. The purification of HBP-fusion proteins can also be achieved in the presence of chemical denaturants, including urea. Additionally, polyclonal antibodies raised against the affinity tag can be used to detect HBP-fused target proteins with high sensitivity. © 2017 by John Wiley & Sons, Inc.

SHuffle™ T7 strain is capable of producing high amount of recombinant human fibroblast growth factor-1 (rhFGF-1) with proper physicochemical and biological properties

BackgroundHuman fibroblast growth factor-1 (FGF-1) has powerful mitogenic activities in a variety of cell types and plays significant roles in many physiological processes e.g. angiogenesis and wound healing. There is increasing demand for large scale production of recombinant human FGF-1 (rhFGF-1), in order to investigate the potential medical use. In the present study, we explored SHuffle™ T7 strain for production of rhFGF-1. MethodsA synthetic gene encoding Met-140 amino acid form of human FGF-1 was utilized for expression of the protein in three different E. coli hosts (BL21 (DE3), Rosetta-gami™ 2(DE3), SHuffle™ T7). Total expressions and soluble/insoluble expression ratios of rhFGF-1 in different hosts were analyzed and compared. Soluble rhFGF-1 produced in SHuffle™ T7 cells was purified using one-step heparin-Sepharose affinity chromatography and characterized by a variety of methods for physicochemical and biological properties. ResultsThe highest level of rhFGF-1 expression and maximum soluble/insoluble ratio were achieved in SHuffle™ T7 strain. Using a single-step heparin-Sepharose chromatography, about 1500mg of purified rhFGF-1 was obtained from one liter of the culture, representing purification yield of ∼70%. The purified protein was reactive toward anti-FGF-1 ployclonal antibody in immunoblotting. Mass spectrometry confirmed the protein had expected amino acid sequence and molecular weight. In reverse-phase high-performance liquid chromatography (RP-HPLC), the protein displayed the same retention time with the human FGF-1 standard, and purity of 94%. Less than 0.3% of the purified protein was comprised of oligomers and/or aggregates as judged by high-performance size-exclusion chromatography (HP-SEC). Secondary and tertiary structures of the protein, investigated by circular dichroism and intrinsic fluorescence spectroscopy methods, respectively, represented native folding of the protein. The purified rhFGF-1 was bioactive and stimulated proliferation of NIH 3T3 cells with EC50 of 0.84ng/mL. ConclusionAlthough SHuffle™ T7 has been introduced for production of disulfide-bonded proteins in cytoplasm, we herein successfully recruited it for high yield production of soluble and bioactive rhFGF-1, a protein with 3 free cysteine and no disulfide bond. To our knowledge, this is the highest-level of rhFGF-1 expression in E. coli reported so far. Extensive physicochemical and biological analysis showed the protein had similar characteristic to authentic FGF-1.

Sperm mitochondrial membrane potential and motility pattern in the Holstein bull semen positive for heparin binding proteins

Present study was aimed to evaluate sperm motility and mitochondrial membrane potential (MMP) in relation to the presence of heparin binding proteins (HBPs) in semen. Semen was collected from 17 Holstein Friesian breeding bulls. Seminal plasma and sperm membrane proteins were isolated by precipitation method; HBPs were isolated using heparin-sepharose affinity chromatography. SDS-PAGE was performed and bulls were categorized into 3 groups based on presence/absence of 24 and 30 kDa HBPs. Computer-assisted semen analysis revealed that fresh ejaculates of bulls positive for 30 kDa HBP had 4.24 and 14.18% of higher total motile sperm than semen with 24 kDa and negative for HBPs. Semen with 30 and 24 kDa had 18.72 and 12.34% of higher number of sperm with progressive motility and velocity than semen devoid of HBPs. Simultaneous assessment of plasma membrane integrity (PMI) and MMP by fluorescence staining revealed that post-thaw sperm of semen with 30 kDa HBP had 6.28 and 12.79% of higher intact PMI. Further, sperm of semen with 30 kDa HBP had 4.61 and 10.50% of higher MMP, which had travelled an extra distance of 9.71 and 4.95 mm through cervical mucus than semen with 24 kDa and devoid of HBPs. The mucus penetration distance showed a strong positive correlation with high MMP, PMI, sperm motility and velocity. It is to be concluded that HBPs were able to sustain higher percentage of motile sperm with progressive motility and MMP which was depicted by more mucus penetration distance.

The presence of heparin binding proteins and their impact on semen quality of Holstein Friesian bulls

Present study was designed to evaluate the semen quality of breeding bulls positive for 24 and 30 kDa heparin binding proteins (HBPs) in the semen. Seventeen Holstein Friesian breeding bulls were screened for 24 and 30 kDa HBPs in semen by heparin-sepharose affinity chromatography and SDS-PAGE, and grouped into three based on presence/absence of HBPs. In vitro characteristics of spermatozoa were assessed by standard analysis of sperm abnormalities, functional membrane integrity, acrosome integrity and sperm chromatin integrity in fresh and frozen- thawed semen. Bulls positive for 30 kDa had lowest sperm abnormalities and sperm chromatin fragmentation than bulls positive for 24 kDa and without HBPs in the fresh ejaculates. Further, fresh semen positive for 30 kDa had 8.76% of higher active plasma membrane with 7.63% intact acrosome. The process of cryopreservation of semen increased sperm abnormalities, acrosome damage and chromatin fragmentation in all the semen samples irrespective of presence/absence of HBPs. However, semen samples positive for 24 and 30 kDa HBPs were able to sustain lower percentage of post-thaw sperm abnormalities with higher chromatin integrity in comparison to semen devoid of HBPs. Moreover, semen with 24 and 30 kDa HBPs had higher post-thaw intact acrosome with active plasma membrane than negative semen. The results concluded that bulls positive for 30 kDa had 12.43 and 28.37 percentages of better semen quality than bulls with 24 kDa and devoid of HBPs.

Abstract A142: The effect of beta2-glycoprotein I on anti-tumor cell migration

Abstract β2-glycoprotein I (β2-GPI) is a multifaceted protein with diverse biological functions, including triglyceride metabolism, blood coagulation and homeostasis. We previously reported that β2-GPI exhibits significant anti-migration effect on human aortic endothelial cells through the NF-κB/eNOS/NO signalling pathway. Migration of endothelial cells has known to be involved in vascular physiology and pathology, such as angiogenesis and tumorigenesis. We thus hypothesize that β2-GPI may also play a critical role in the regulation of tumor cell migration and invasion. Human plasma protein was precipitated by 3% (v/v) perchloric acid and β2-GPI was purified by heparin-Sepharose affinity chromatography. The purity of β2-GPI was determined by SDS/PAGE and Western blot analysis. The influence of β2-GPI on tumor cell migration was analyzed by wound healing and trans-well migration analysis. Using wound healing assay, we found that purified β2-GPI was able to inhibit cell migration in various tumor cancers, such as A375 human melanoma cancer cells, B16-F10 mouse melanoma cells, oral squamous cell carcinoma (OSCC)-derived cell line human tongue squamous carcinoma (SAS), and human head neck squamous cell carcinoma (HNSCC) cell lines FaDu (hypopharyngeal) carcinoma. In the trans-well assay, β2-GPI also showed markedly inhibition of tumor cell migration from the upper chamber to the lower chamber. Furthermore, β2-GPI revealed dose-dependently anti-invasion effect on melanoma cancer cells. The findings of the present study provide insight into the ability of β2-GPI to inhibit tumor cell migration, which indicates a novel direction for its application in anti-cancer therapy. Citation Format: An-Na Chiang, Wan-Chun Li, Shu-Hau Yeh, Shu-Wei Cheng, Yu-Shan Lin. The effect of beta2-glycoprotein I on anti-tumor cell migration. [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2015 Nov 5-9; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2015;14(12 Suppl 2):Abstract nr A142.

Chemokines and Glycosaminoglycans.

OPINION article Front. Immunol., 26 May 2015Sec. Cytokines and Soluble Mediators in Immunity Volume 6 - 2015 | https://doi.org/10.3389/fimmu.2015.00246

Interaction of phospholipid transfer protein with human tear fluid mucins

In addition to circulation, where it transfers phospholipids between lipoprotein particles, phospholipid transfer protein (PLTP) was also identified as a component of normal tear fluid. The purpose of this study was to clarify the secretion route of tear fluid PLTP and elucidate possible interactions between PLTP and other tear fluid proteins. Human lacrimal gland samples were stained with monoclonal antibodies against PLTP. Heparin-Sepharose (H-S) affinity chromatography was used for specific PLTP binding, and coeluted proteins were identified with MALDI-TOF mass spectrometry or Western blot analysis. Immunoprecipitation assay and blotting with specific antibodies helped to identify and characterize PLTP-mucin interaction in tear fluid. Human tear fluid PLTP is secreted from the lacrimal gland. MALDI-TOF analysis of H-S fractions identified several candidate proteins, but protein-protein interaction assays revealed only ocular mucins as PLTP interaction partners. We suggest a dual role for PLTP in human tear fluid: (1) to scavenge lipophilic substances from ocular mucins and (2) to maintain the stability of the anterior tear lipid film. PLTP may also play a role in the development of ocular surface disease.

Characterization of a Recombinant Form of Annexin VI for Detection of Apoptosis

We developed a recombinant form of human annexin VI called annexin VI-601 (M(r) 76,224) with the N-terminal extension of Ala-Gly-Gly-Cys-Gly-His to allow ready attachment of fluorescent or radioactive labels. The protein was produced by expression in E. coli and was purified by calcium-dependent membrane binding, anion-exchange chromatography, and heparin-Sepharose affinity chromatography. The protein could be readily labeled with iodoacetamidofluorescein and with (99m)Tc. The protein bound with high affinity to PS-containing phospholipid vesicles and to erythrocytes with exposed phosphatidylserine. Fluorescent annexin VI-601 readily detected apoptosis of Jurkat cells by flow cytometry at much lower calcium concentrations than those required for equivalent detection by annexin V. In vivo administration of radiolabeled protein showed that blood clearance was much slower than annexin V. In conclusion, annexin VI may have advantages over annexin V in certain situations for both in vitro and in vivo detection of apoptosis and therapeutic targeting of PS due to its lower calcium requirement for membrane binding and its higher molecular weight.

Conformational and biochemical characterization of a biologically active rat recombinant Protease Nexin-1 expressed in E. coli

Protease Nexin-1, a 43-kDa glycoprotein, is a major physiological thrombin inhibitor involved in the modulation of nerve cell plasticity. Recombinant rat Protease Nexin-1 (rPN-1) was efficiently produced in Escherichia coli using a T7 RNA polymerase based expression system and purified by heparin-sepharose affinity chromatography yielding 3 mg of protein per liter of cell culture. The purity and chemical identity of rPN-1 were assessed by SDS-PAGE, Reverse Phase- High Performance Liquid Chromatography, mass spectrometry and two-dimensional-gel electrophoresis. Conformational analysis by circular dichroism and fluorescence spectroscopy revealed the presence of mixed α/β secondary structure and the prevailing localization of Trp-residues in rather polar environments. Fluorescence titration of rPN-1 with heparin indicated that rPN-1 binds heparin with high affinity. Furthermore, the formation of a SDS-stable 1:1 thrombin–rPN-1 complex, monitored by SDS-PAGE, confirmed the native-like structure of rPN-1. Finally, the cellular effects of rPN-1, such as its ability to promote neurite outgrowth in neuroblastoma cells, were found to be very similar to those elicited by natural PN-1. Altogether, our results demonstrate that glycosylation does not alter neither structure nor function of PN-1 and that E. coli is a suitable expression system for obtaining milligram quantities of pure and fully active rPN-1 for structural and functional studies.

Identification of the heparin-binding domain of TNF-alpha and its use for efficient TNF-alpha purification by heparin–Sepharose affinity chromatography

The N-terminus of the trimeric TNF-alpha molecule comprises two basic arginines within the short amino-acid sequence VRSSSR, which is here shown to be essential for binding of TNF-alpha to heparin–Sepharose. Mixed trimers containing full-length and ΔN6-truncated subunits revealed a single VRSSSR sequence to be sufficient to achieve binding. On the basis of this newly identified heparin-binding domain, a new method for efficient purification of TNF-alpha is described. Affinity chromatography on heparin–Sepharose was introduced as a key step for highly purified TNF-alpha at a high yield. With minor modifications, this procedure can be used for TNF-alpha analogues that have full-length N-termini, as shown for the less toxic analogue LK-805.

Trypanosoma cruzi heparin-binding proteins and the nature of the host cell heparan sulfate-binding domain

Trypanosoma cruzi invasion is mediated by receptor–ligand recognition between the surfaces of both parasite and target cell. We have previously demonstrated the role of heparan sulfate proteoglycan in the attachment and invasion of T. cruzi in cardiomyocytes. Herein, we have isolated the T. cruzi heparin-binding proteins (HBP-Tc) and investigated the nature of cardiomyocyte heparan sulfate (HS)-binding site to the parasite surface ligand. Two major heparin-binding proteins with molecular masses of 65.8 and 59 kDa were observed in total extract of amastigote and trypomastigote forms of T. cruzi. Hydrophobic [S 35]methionine labeled proteins eluted from heparin–sepharose affinity chromatography also revealed both proteins in trypomastigotes but only the 59 kDa is strongly recognized by biotin-conjugated glycosaminoglycans. Competition assays were performed to analyze the role of sulfated proteoglycans, including heparin, keratan sulfate and both acetylated and highly sulfated domains of heparan sulfate, in the recognition and invasion process of T. cruzi. Significant inhibitions of 84% and 35% in the percentage of infection were revealed after treatment of the parasites with heparin and the N-acetylated/ N-sulfated heparan sulfate domain, respectively, suggesting the important role of the glycuronic acid and NS glucosamine domain of the HS chain in the recognition of the HBP-Tc during the T. cruzi–cardiomyocyte interaction.

Determination of Bovine Serum Low-density Lipoprotein Cholesterol using the N-geneous Method

The N-geneous method is a recently developed method for determination of low-density lipoprotein cholesterol (LDL-C) in human serum. In the present study, we attempted to adapt this method to bovine serum. The values of LDL-C obtained using the N-geneous method were highly correlated with those from the method using ultracentrifugation and heparin sepharose affinity chromatography (r = 0.934, p < 0.001). The reproducibility of this method was acceptable (intra-assay CV 4.2%, inter-assay CV 7.6%) for clinical use. Using the N-geneous method, serum LDL-C was evaluated in cows around parturition, and in cows with fatty liver induced by fasting. The concentration of LDL-C decreased significantly in cows close to parturition. A reduced concentration of LDL-C was also observed in cows with fatty liver. In both cases, the changes of LDL-C were similar to those of apolipoprotein B (apoB)-100, and the values of LDL-C were highly correlated (r = 0.876, p < 0.001) with those of apoB-100. These results suggest that the concentration of LDL-C reflects the level of apoB-100. The N-geneous method is simple and rapid, and might to be a useful tool to elucidate the clinical significance of LDL-C in bovine serum.

Localization of the heparin binding site in human apolipoprotein AV

Apolipoprotein (apo) A-V is a potent modulator of plasma triacylglycerol (TG) levels. The molecular basis for this activity is not understood. Recent studies have shown that apoA-V possesses heparin binding activity. A stretch of 42 amino acids (residue 186 to 227) in apoA-V has been identified by sequence analysis to contain 5 arginines, 3 lysines, 4 histidines and no negatively charged amino acids. This segment is hypothesized to be the heparin binding region of apoA-V. To test this, site directed mutagenesis was used to generate three mutations in this region, in which positively charged amino acids were replaced by either negatively charged or uncharged polar amino acids. The resulting mutatants (R210E/K211Q-apoA-V, K215Q/K217E-apoA-V, and R210E/K211Q/K215Q/K217E-apoA-V) were complexed with dimyristoylphosphatidylcholine (DMPC) and subjected to heparin Sepharose affinity chromatography and surface plasmon resonance spectroscopy using a heparin-coated sensor chip. With both methods of analysis, compared to WT apoA-V DMPC complexes, the mutants showed decreased affinity for heparin. These results show that positively charged residues between position 186 and 227 of human apoA-V contribute to heparin binding. This region of apoA-V may play an important role in cell surface interactions by binding with heparan sulfate proteogylcans, indirectly affecting lipoprotein lipase activity, possibly contributing to apoA-V’s ability to influence plasma TG levels. Supported by NIH.

Endothelial and lipoprotein lipases in human and mouse placenta

Placenta expresses various lipase activities. However, a detailed characterization of the involved genes and proteins is lacking. In this study, we compared the expression of endothelial lipase (EL) and LPL in human term placenta. When placental protein extracts were separated by heparin-Sepharose affinity chromatography, the EL protein eluted as a single peak without detectable phospholipid or triglyceride (TG) lipase activity. The major portion of LPL protein eluted slightly after EL. This peak also had no lipase activity and most likely contained monomeric LPL. Fractions eluting at a higher NaCl concentration contained small amounts of LPL protein (most likely dimeric LPL) and had substantial TG lipase activity. In situ hybridization studies showed EL mRNA expression in syncytiotrophoblasts and endothelial cells and LPL mRNA in syncytiotrophoblasts. In contrast, immunohistochemistry showed EL and LPL protein associated with both cell types. In mouse placentas, lack of LPL expression resulted in increased EL mRNA expression. These results suggest that the cellular expression of EL and LPL in human placenta is different. Nevertheless, the two lipases might have overlapping functions in the mouse placenta. Our data also suggest that the major portions of both proteins are stored in an inactive form in human term placenta.

Role of Chloride Ions in Modulation of the Interaction between von Willebrand Factor and ADAMTS-13

The degradation of von Willebrand factor (VWF) depends on the activity of a zinc protease (referred to as ADAMTS-13), which cleaves VWF at the Tyr(1605)-Met(1606) peptide bond. Little information is available on the physiological mechanisms involved in regulation of AD-AMTS-13 activity. In this study, the role of ions on the ADAMTS-13/VWF interaction was investigated. In the presence of 1.5 m urea, the protease cleaved multimeric VWF in the absence of NaCl at pH 8.00 and 37 degrees C, with an apparent k(cat)/K(m) congruent with 3.4 x 10(4) M(-1) s(-1), but this value decreased by approximately 10-fold in the presence of 0.15 M NaCl. Using several monovalent salts, the inhibitory effect was attributed mostly to anions, whose potency was inversely related to the corresponding Jones-Dole viscosity B coefficients (ClO(4)(-) > Cl(-) > F(-)). The specific inhibitory effect of anions was due to their binding to VWF, which caused a conformational change responsible for quenching the intrinsic fluorescence of the protein and reducing tyrosine exposition to bulk solvent. Ristocetin binding to VWF could reduce the apparent affinity and reverse the inhibitory effect of chloride. We hypothesize that, after secretion into the extracellular compartment, VWF is bound by chloride ions abundantly present in this milieu, becoming unavailable to proteolysis by AD-AMTS-13. Shear forces, which facilitate GpIbalpha binding (this effect being artificially obtained by ristocetin), can reverse the inhibitory effect of chloride, whose concentration gradient across the cell membrane may represent a simple but efficient strategy to regulate the enzymatic activity of ADAMTS-13.

Characterization of recombinant human protein C inhibitor expressed in Escherichia coli

The serine protease inhibitor (serpin) protein C inhibitor (PCI; also named plasminogen activator inhibitor-3) regulates serine proteases in hemostasis, fibrinolysis, and reproduction. The biochemical activity of PCI is not fully defined partly due to the lack of a convenient expression system for active rPCI. Using pET-15b plasmid, Ni 2+-chelate and heparin-Sepharose affinity chromatography steps, we describe here the expression, purification and characterization of wild-type recombinant (wt-rPCI) and two inactive mutants, R354A (P1 residue) and T341R (P14 residue), expressed in Escherichia coli. Wild-type rPCI, but not the two mutants, formed a stable bimolecular complex with thrombin, activated protein C and urokinase. In the absence of heparin, wt-rPCI-thrombin, -activated protein C, and -urokinase inhibition rates were 56.7, 3.4, and 2.3×10 4 M −1 min −1, respectively, and the inhibition rates were accelerated 25-, 71-, and 265-fold in the presence of 10 μg/mL heparin for each respective inhibition reaction. The stoichiometry of inhibition (SI) for wt-rPCI-thrombin was 2.0, which is comparable to plasma-derived PCI. The present report describes for the first time the expression and characterization of recombinant PCI in a bacterial expression system and demonstrates the feasibility of using this system to obtain adequate amounts of biologically active rPCI for future structure–function studies.