Purification of lysozyme from other hen's-egg-white proteins using metal-affinity precipitation

Engineering Pichia pastoris for Efficient Production of a Novel Bifunctional Strongylocentrotus purpuratus Invertebrate-Type Lysozyme

Lysozymes are known as ubiquitously distributed immune effectors with hydrolytic activity against peptidoglycan, the major bacterial cell wall polymer, to trigger cell lysis. In the present study, the full-length cDNA sequence of a novel sea urchin Strongylocentrotus purpuratus invertebrate-type lysozyme (sp-iLys) was synthesized according to the codon usage bias of Pichia pastoris and was cloned into a constitutive expression plasmid pPIC9K. The resulting plasmid, pPIC9K-sp-iLys, was integrated into the genome of P. pastoris strain GS115. The bioactive recombinant sp-iLys was successfully secreted into the culture broth by positive transformants. The highest lytic activity of 960 U/mL of culture supernatant was reached in fed-batch fermentation. Using chitin affinity chromatography and gel-filtration chromatography, recombinant sp-iLys was produced with a yield of 94.5 mg/L and purity of > 99%. Recombinant sp-iLys reached its peak lytic activity of 8560 U/mg at pH 6.0 and 30 °C and showed antimicrobial activities against Gram-negative bacteria (Vibrio vulnificus, Vibrio parahemolyticus, and Aeromonas hydrophila) and Gram-positive bacteria (Staphylococcus aureus and Bacillus subtilis). In addition, recombinant sp-iLys displayed isopeptidase activity which reached the peak at pH 7.5 and 37 °C with the presence of 0.05 M Na⁺. In conclusion, this report describes the heterologous expression of recombinant sp-iLys in P. pastoris on a preparative-scale, which possesses lytic activity and isopeptidase activity. This suggests that sp-iLys might play an important role in the innate immunity of S. purpuratus.

Efficient production of human goose-type lysozyme 2 in the methylotrophic yeast Pichia pastoris

Infectious diseases caused by antibiotic multidrug-resistant microorganisms are major causes of morbidity and mortality in humans. Hence, there is an urgent need to search for new antimicrobial agents. Initially known as a defensive effector in the innate immunity of certain organs of the human body, human goose-type lysozyme 2 (hLysG2) has been shown to possess therapeutically useful potential against multidrug-resistant microorganisms. Developing a novel strategy for large-scale production that provides high yields of this protein with high purity, quality, and potency is critical for pharmaceutical applications. To overcome the issues related to prokaryotic expression, here we report the production of recombinant hLysG2 (rhLysG2) using the methylotrophic yeast Pichia pastoris as expression host. The strong inducible alcoholoxidase 1 (AOX1) promoter was used to drive expression of the optimized hLysG2 gene. Under the optimal expression conditions, the lytic activity of rhLysG2 reached 113 U/mL of culture supernatant in shake flask cultivation and this was increased to 2084 U/mL in fed-batch fermentation. Using chitin affinity chromatography and size-exclusion chromatography, rhLysG2 was produced with a yield of 137 mg/L, purity of > 99%, molecular weight of 21,504.6 Da, and specific activity of 13,500 U/mg. In vitro assays indicated that rhLysG2 possessed muramidase activity, isopeptidase activity, and free radical scavenging activity. This report describes an efficient strategy for the production of biologically active rhLysG2 in P. pastoris on a large scale with a high yield, which provides a solid foundation for possible future pharmaceutical applications.

Role of electric field on surface wetting of polystyrene surface

The role of surface charge in fluid flow in micro/nanofluidics systems as well as the role of electric field to create switchable hydrophobic surfaces is of interest. In this work, the contact angle (CA) and contact angle hysteresis (CAH) of a droplet of deionized (DI) water were measured with applied direct current (DC) and alternating current (AC) electric fields. The droplet was deposited on a polystyrene (PS) surface, commonly used in various nanotechnology applications, coated on a doped silicon (Si) wafer. With the DC field, CA decreased with an increase in voltage. Because of the presence of a silicon oxide layer and a space charge layer, the change of the CA was found to be lower than with a metal substrate. The CAH had no obvious change with a DC field. An AC field with a positive value was applied to the droplet to study its effect on CA and CAH. At low frequency (lower than 10 Hz), the droplet was visibly oscillating. The CA was found to increase when the frequency of the applied AC field increased from 1 Hz to 10 kHz. On the other hand, the CA decreased with an increasing peak-peak voltage at or lower than 10 kHz. The CAH in the AC field was found to be lower than in the DC field and had a similar trend to static CA with increasing frequency. A model is presented to explain the data.

Biomimetic micro∕nanostructured functional surfaces for microfluidic and tissue engineering applications

This paper reviews our work on the application of ultrafast pulsed laser micro∕nanoprocessing for the three-dimensional (3D) biomimetic modification of materials surfaces. It is shown that the artificial surfaces obtained by femtosecond-laser processing of Si in reactive gas atmosphere exhibit roughness at both micro- and nanoscales that mimics the hierarchical morphology of natural surfaces. Along with the spatial control of the topology, defining surface chemistry provides materials exhibiting notable wetting characteristics which are potentially useful for open microfluidic applications. Depending on the functional coating deposited on the laser patterned 3D structures, we can achieve artificial surfaces that are (a) of extremely low surface energy, thus water-repellent and self-cleaned, and (b) responsive, i.e., showing the ability to change their surface energy in response to different external stimuli such as light, electric field, and pH. Moreover, the behavior of different kinds of cells cultured on laser engineered substrates of various wettabilities was investigated. Experiments showed that it is possible to preferentially tune cell adhesion and growth through choosing proper combinations of surface topography and chemistry. It is concluded that the laser textured 3D micro∕nano-Si surfaces with controllability of roughness ratio and surface chemistry can advantageously serve as a novel means to elucidate the 3D cell-scaffold interactions for tissue engineering applications.

Use of magnetic poly(glycidyl methacrylate) monosize beads for the purification of lysozyme in batch system

The hydrophobic affinity ligand L-tryptophan immobilized magnetic poly(glycidyl methacrylate) [m-poly(GMA)] beads in monosize form (1.6 microm in diameter) were used for the affinity purification of lysozyme from chicken egg white. The m-poly(GMA) beads were prepared by dispersion polymerization in the presence of Fe3O4 nano-powder. The epoxy groups of the m-poly(GMA) beads were converted into amino groups with 1,6 diaminohexane (i.e., spacer arm). l-tryptophan was then covalently immobilized on spacer arm attached m-poly(GMA) beads. Elemental analysis of immobilised L-tryptophan for nitrogen was estimated as 42.5 micromol/g polymer. Adsorption studies were performed under different conditions in a batch system (i.e., medium pH, protein concentration and temperature). Maximum lysozyme adsorption amount of m-poly(GMA) and m-poly(GMA)-L-tryptophan beads were 1.78 and 259.6 mg/g, respectively. The applicability of two kinetic models including pseudo-first order and pseudo-second order model was estimated on the basis of comparative analysis of the corresponding rate parameters, equilibrium adsorption capacity and correlation coefficients. Results suggest that chemisorption processes could be the rate-limiting step in the adsorption process. It was observed that after 10 adsorption-elution cycle, m-poly(GMA)-L-tryptophan beads can be used without significant loss in lysozyme adsorption capacity. Purification of lysozyme from egg white was also investigated. Purification of lysozyme was monitored by determining the lysozyme activity using Micrococcus lysodeikticus as substrate. It was found to be successful in achieving purification of lysozyme in a high yield of 76% with a purification fold of 71 in a single step. The specific activity of the eluted lysozyme (62,580 U/mg) was higher than that obtained with a commercially available pure lysozyme (Sigma (60,000 U/mg).

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.

Single step immobilized metal ion affinity precipitation/chromatography based procedures for purification of concanavalin A and Cajanus cajan mannose-specific lectin

Concanavalin A and a mannose-specific lectin could be precipitated specifically from extracts of jack bean and Cajanus cajan seeds, respectively, using metal charged EGTA. Single step purification of the lectins was also possible using iminodiacetic acid-Sepharose charged with metal ions. Nondenaturing electrophoresis in polyacrylamide gel and that performed in presence of SDS ascertained homogeneity of the isolated lectins. The migration behavior of the purified lectins was comparable with those of the lectins purified using alternative procedures.

Purification of green fluorescent protein overexpressed by a mutant recombinant Escherichia coli

Green fluorescent protein was purified from sonicated recombinant Escherichia coli and its mutant obtained after exposure to UV light. The latter overexpresses green fluorescent protein. The two-step procedure consisted of a two-phase aqueous extraction with PEG/salt and precipitation of the proteins from PEG phase by free Zn2+. The recoveries of green fluorescent protein were 73 and 83% in the cases of recombinant E. coli and its mutant, respectively. The corresponding fold purifications were 24 and 9, respectively. In both cases, the purified protein showed a single band on SDS-PAGE corresponding to 28 kDa.