Generation of a new protein purification matrix by loading ceramic hydroxyapatite with metal ions--demonstration with poly-histidine tagged green fluorescent protein

Immobilization of foreign protein into polyhedra of Bombyx mori nucleopolyhedrovirus (BmNPV)

In the late phase of Bombyx mori nucleopolyhedrovirus (BmNPV) infection, a large amount of polyhedra appear in the infected cell nucleolus, these polyhedra being dense protein crystals protecting the incorporated virions from the harsh environment. To investigate whether the foreign protein could be immobilized into the polyhedra of BmNPV, two recombinant baculoviruses were generated by a novel BmNPV polyhedrin-plus (polh(+)) Bac-to-Bac system, designated as vBmBac(polh(+))-enhanced green fluorescent protein (EGFP) and vBmBac(polh(+))-LacZ, which can express the polyhedrin and foreign protein simultaneously. Light microscopy analysis showed that all viruses produced polyhedra of normal appearance. Green fluorescence can be apparently detected on the surface of the vBmBac(polh(+))-EGFP polyhedra, but not the BmNPV polyhedra. Fluorescence analysis and anti-desiccation testing confirmed that EGFP was embedded in the polyhedra. As expected, the vBmBac(polh(+))-LacZ polyhedra contained an amount of LacZ and had a higher β-galactosidase activity. Sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) and Western blotting were also performed to verify if the foreign proteins were immobilized into polyhedra. This study provides a new inspiration for efficient preservation of useful proteins and development of new pesticides with toxic proteins.

Organic/Inorganic bioactive materials Part III: in vitro bioactivity of gelatin/silicocarnotite hybrids

In this work we present our experimental results on synthesis, structure evolution and in vitro bioactivity assessment of new gelatin/silicocarnotite hybrid materials. The hybrids were obtained by diluting gelatin (G) and silicocarnotite (S) ceramic powder with G:S ratios of 75:25 and 25:75 wt.% in hot (40°C) water. The hybrids were characterized using XRD, FTIR, SEM/EDS and XPS. FTIR depicts that the “red shift” of amide I and COO− could be attributed to the fact that the gelatin prefers to chelate Ca2+ from S. The growth of calcium phosphates on the surface of the hybrids synthesized and then immersed in 1.5 SBF for 3 days was studied by using of FTIR, XRD and SEM/EDS. According to FTIR results, after an immersion of 3 days, A and B-type CO3HA can be observed on the surface. XRD results indicate the presence of hydroxyapatite with well defined crystallinity. SEM/EDS of the precipitated layers show the presence of CO3HA and amorphous calcium phosphate on the surface of samples with different G/S content when immersed in 1.5 SBF. XPS of the G/S hybrid with 25:75 wt.% proved the presence of Ca-deficient hydroxyapatite after an in vitro test for 3 days.

Combining chemistry and biology to create colloidally stable bionanohydroxyapatite particles: toward load-bearing bone applications

This study presents a layer by layer assembly on nanohydroxyapatite (nHA) particles with the dual aim of enhancing particle dispersion and biological response to produce superior reinforcements intended for load-bearing applications. The system tested consists of three sequential biological polyelectrolyte layers of heparin (representing glycosaminoglycans), polyhistidine (representing growth factors), and heparin adsorbed onto nHA. The results reveal that the resulting bio-nHA particles with an outer heparin layer are colloidally stable in aqueous solution for 23 days. Adsorption isotherms combined with Ca(2+) release studies allowed a detailed description of each adsorbed layer. Release patterns for each adsorbed layer reveal that the biological polyelectrolytes are, at least in part, released as polyelectrolyte complexes. In conclusion, the combination of its colloidal dispersant properties and osteoinductive potential make the developed bio-nHA particles promising reinforcements to improve current composite biomaterials or bone-engineering scaffolds toward load-bearing dental and orthopedic applications.

Internalization of hydroxyapatite nanoparticles in liver cancer cells

Hydroxyapatite (HAP) is the main inorganic component of hard tissues and shows excellent biocompatibility and osteoconductivity properties. Nanoparticles of HAP can be synthesised by the precipitation method in distilled water. The needle shaped particles are below 100 nm in size with low-crystallinity and high-surfacial activation. Recent studies showed toxic effects of HAP nanoparticles on cancer cells. Other studies focus on the application of HAP nanoparticles as drug and gene delivery system or cell marker. However, to date, the exact internalization pathway of HAP nanoparticles into cells has not been determined. When HAP nanoparticles were added to cell culture medium, the particles immediately became instable and formed agglomerates with a size of about 500-700 nm. Hence, cells seldom encounter single HAP nanoparticles in the environment of cell culture or body fluid. The TEM showed internalized HAP captured by vacuoles in the cytoplasm of the hepatocellular carcinoma cells. The invaginations in the cell membrane before nanoparticle uptake suggested endocytic pathways as internalization mechanism. This study revealed that agglomerated HAP nanoparticles were internalized by cells through the energy-dependent process of clathrin-mediated endocytosis. Depletion of intracellular potassium arrested the formation of coated pit, which inhibited the uptake of HAP.

Use of an alternative scale-down approach to predict and extend hydroxyapatite column lifetimes

Ceramic hydroxyapatite (CHT) chromatography offers unique selectivity for protein purification. However, columns composed of CHT, a crystalline form of calcium phosphate, often suffer from short column lifetimes, particularly under acidic operating conditions. In this paper, CHT was used under slightly acidic conditions (pH 6) for the production scale purification of a recombinant protein. Under these conditions, the packing quality of production scale CHT columns (45 cm diameter) degraded after 5-10 cycles of operation. This was not reproduced using a conventional scale-down chromatography model, in which a constant column bed height was maintained across scales. Thus, an alternative scale-down model was developed to better predict the lifetime of large scale CHT columns. The alternative approach, which utilized a constant column diameter-to-height aspect ratio, was able to predict column failure that approximated that of the manufacturing scale column. The alternative scale-down approach was then used to test alternate buffer formulations that significantly improved the CHT column lifetime. Screening studies, which assessed the effects of mobile phase pH and composition on the dissolution (weight loss) of CHT, were used to identify the alternative mobile phase formulations. Results from the study showed that slight changes to the existing mobile phase compositions significantly increased the column lifetime, from approximately 10 cycles to approximately 65 cycles of use, without altering the purification of the recombinant protein. The alternative scale-down model, together with relatively rapid mobile phase screening studies, provides a practical approach for predicting and optimizing the useful lifetime of CHT columns for large scale applications.

The affinity concept in bioseparation: Evolving paradigms and expanding range of applications

The meaning of the word affinity in the context of protein separation has undergone evolutionary changes over the years. The exploitation of molecular recognition phenomenon is no longer limited to affinity chromatography modes. Affinity based separations today include precipitation, membrane based purification and two-phase/three-phase extractions. Apart from the affinity ligands, which have biological relationship (in vivo) with the target protein, a variety of other ligands are now used in the affinity based separations. These include dyes, chelated metal ions, peptides obtained by phage display technology, combinatorial synthesis, ribosome display methods and by systematic evolution of ligands by exponential enrichment (SELEX). Molecular modeling techniques have also facilitated the designing of biomimetic ligands. Fusion proteins obtained by recombinatorial methods have emerged as a powerful approach in bioseparation. Overexpression in E. coli often result in inactive and insoluble inclusion bodies. A number of interesting approaches are used for simultaneous refolding and purification in such cases. Proteomics also needs affinity chromatography to reduce the complexity of the system before analysis by electrophoresis and mass spectrometry are made. At industrial level, validation, biosafety and process hygiene are also important aspects. This overview looks at these evolving paradigms and various strategies which utilize affinity phenomenon for protein separations.

Molecular characterization of a β-1,4-endoglucanase from an endophytic Bacillus pumilus strain

Endophytes comprise mainly microorganisms that colonize inner plant tissues, often living with the host in a symbiotic manner. Several ecological roles have been assigned to endophytic fungi and bacteria, such as antibiosis to phytopathogenic agents and plant growth promotion. Nowadays, endophytes are viewed as a new source of genes, proteins and biochemical compounds that may be used to improve industrial processes. In this study, the gene EglA was cloned from a citrus endophytic Bacillus strain. The EglA encodes a beta-1,4-endoglucanase capable of hydrolyzing cellulose under in vitro conditions. The predicted protein, EglA, has high homology to other bacterial cellulases and shows a modular structure containing a catalytic domain of the glycosyl hydrolase family 9 (GH9) and a cellulose-binding module type 3 (CBM3). The enzyme was expressed in Escherichia coli, purified to homogeneity, and characterized. EglA has an optimum pH range of 5-8, and remarkable heat stability, retaining more than 85% activity even after a 24-h incubation at pH 6-8.6. This characteristic is an important feature for further applications of this enzyme in biotechnological processes in which temperatures of 50-60 degrees C are required over long incubation periods.

Characterization of metal affinity of green fluorescent protein and its purification through salt promoted, immobilized metal affinity chromatography

Immobilized metal affinity chromatography (IMAC) was investigated as a method of recovery for green fluorescent protein (GFPuv). It was found that in the absence of genetic modification to enhance metal affinity, GFPuv displayed strong metal affinity to Cu(II) and Ni(II), and weak or negligible affinity to Zn(II) and Co(II). Changes in the mobile phase NaCl concentration during Ni(II)-IMAC strongly affected purity and yield of GFPuv, with fine resolution under higher NaCl concentrations. Finally, IMAC via Cu(II) and Zn(II) with intervening diafiltration was used to recover GFPuv with high yield and purity.

A baculovirus superinfection system: efficient vehicle for gene transfer into Drosophila S2 cells

The baculovirus expression vector system is considered to be a safe, powerful, but cell-lytic heterologous protein expression system in insect cells. We show here that there is a new baculovirus system for efficient gene transfer and expression using the popular and genetically well-understood Drosophila S2 cells. The recombinant baculovirus was constructed to carry an enhanced green fluorescent protein under the control of polyhedrin promoter as a fluorescent selection marker in the Sf21 cell line. Recombinant baculoviruses were then used to transduce S2 cells with target gene expression cassettes containing a Drosophila heat shock protein 70, an actin 5C, or a metallothionein promoter. Nearly 100% of the S2 cells showed evidence of gene expression after infection. The time course for the optimal protein expression peaked at 24 to 36 h postinfection, which is significantly earlier than a polyhedrin-driven protein expression in Sf21 cells. Importantly, S2 cells did not appear to be lysed after infection, and the protein expression levels are comparable to those of proteins under the control of polyhedrin promoter in several lepidopteran cell lines. Most surprisingly, S2 cells permit repetitive infections of multiple baculoviruses over time. These findings clearly suggest that this baculovirus-S2 system may effect the efficient gene transfer and expression system of the well-characterized Drosophila S2 cells.

Discoloration of ceramic hydroxyapatite used for protein chromatography

Hydroxyapatite chromatography was used to purify a recombinant human protein at preparative (400 g) scale. The hydroxyapatite column became progressively discolored as the number of chromatographic cycles increased. Elemental analysis showed that Mn, Fe, Al, Cd, Ba, Cr and Sn were found in used, discolored hydroxyapatite but were below the detection limit (1 ppm) in new hydroxyapatite. Metal ions were not removed from the discolored hydroxyapatite by regeneration with 0.5 M sodium phosphate followed by 0.5 M sodium hydroxide. Chromatographic performance was not affected by the accumulation of metal ions for at least 8 cycles on the preparative column (media volume 56 l) and for at least 12 cycles on the laboratory-scale column (media volume 3.7 ml).