High-level production of recombinant chicken cystatin by Pichia pastoris and its application in mackerel surimi

Egg White Cystatin – A Review

Hen eggs are widely used, not only for human consumption, but also as an important material in food production and in pharmaceutical and cosmetics industry. Cystatin is a biologically active component of egg white, mostly used as an inhibitor of papain-like cysteine proteases. It was isolated from chicken egg white and has later been used in the nomenclature of structurally and functionally related proteins. Cystatins from animals, including mouse, rat, dog, cow and chicken egg white have been isolated and recently used in foodstuffs and drug administration. Cystatin has found its place and use in medicine due to its antimicrobial, antiviral and insecticidal effects, for the prevention of cerebral hemorrhage and control of cancer cell metastasis.

Structural Characteristics of Hen Egg Ovalbumin Expressed in YeastPichia pastoris

The recombinant ovalbumin (OVA) produced in yeast Pichia pastoris was purified from the culture medium by anion exchange chromatography, and its structural characteristics were compared with those of hen egg OVA, mainly from the point of view of posttranslational modification. The expressed OVA consisted of two molecular species immmunoreactive with antibody for hen egg OVA. The two molecular species, 45 and 47 kDa in molecular size, were thought to correspond to mono-glycosylated form and di-glycosylated form respectively. The non-glycosylated form was not produced in the system. The other posttranslational modifications (N-terminal acetylation and phosphorylation) observed in hen egg OVA were not detected in either of the molecular species. The two recombinant proteins displayed almost exactly the same circular dichroism and intrinsic tryptophan fluorescence spectra as hen egg OVA. The melting temperature, Tm, which was determined from the thermal unfolding curve, was almost identical in the two recombinant proteins, despite the difference in glycosylation levels, while it decreased by about 2.5 degrees C as compared with that of hen egg OVA (77.3 degrees C). These data indicate that the additional glycosylation to Asn-311 in the recombinant protein does not affect protein conformation or thermostability.

Diffusion of active proteins into fish meat to minimize proteolytic degradation

Proteases in fish muscle often cause undesired softening of intact meat pieces during refrigerated storage or slow cooking. Several food-grade proteinaceous inhibitors can overcome this softening if properly delivered to the intracellular sites where proteases are located. Fluorescence recovery after photobleaching (FRAP) and laser scanning confocal microscopy (LSCM) were used to measure the translational diffusion of fluorescein isothiocyanate (FITC)-labeled protease inhibitors into intact muscle fibers of halibut. Diffusion coefficients (D) of alpha-2-macroglobulin (720 kDa), soybean trypsin inhibitor (21 kDa), and cystatin (12 kDa) were measured in both muscle fibers and dilute aqueous solutions. On the time scale of the observation (35 min), cystatin and soybean trypsin inhibitor diffused through the cell membrane (sarcolemma) and sarcoplasm, but at a considerably slower rate (>10-fold difference) than in dilute aqueous solution. alpha-2-Macroglobulin did not diffuse into muscle cells within the time frame of the experiment, but did completely penetrate the cell during overnight exposure. The present study thus shows a clear dependence of D on protein inhibitor size when moving within intact skeletal muscle fibers. Low molecular weight protease inhibitors such as cystatin can be effectively diffused into intact fish muscle cells to minimize proteolytic activity and meat softening.

Application of recombinant chum salmon cystatin to Alaska pollock (Theragra chalcogramma) surimi to prevent gel weakening

Recombinant chum salmon cystatin (RC) expressed in Saccharomyces cerevisiae was purified by His-select nickel affinity chromatography. The specific inhibitory activities of RC against papain and cathepsin L were 7.45 and 10.24 U/mg, respectively. RC was stable over pH 5.0 to 7.0 and at temperature below 65 degrees C. RC was used to prevent the gel weakening of Alaska pollock surimi. RC at 100 microg/g showed the highest inhibitory activity against the autolysis of surimi based on the analysis of TCA-soluble peptides. As the concentration of RC increased, both the breaking force and deformation of modori gel greatly increased (P < 0.05). The addition of RC resulted in less expressible drip, which coincided with the increase of whiteness. More myosin heavy chain (MHC) was retained as the addition of RC increased. Therefore, RC could prevent the degradation of proteins in Alaska pollock surimi and was better than egg white (EW). Thus, RC could be applied to Alaska pollock surimi to prevent gel weakening and RC at 100 microg/g was the optimal concentration.

Secretory and continuous expression of Aspergillus niger glucose oxidase gene in Pichia pastoris

We proposed a yeast transformant cell incorporating the Aspergillus niger glucose oxidase gene (GOX gene), which is capable of constitutively as well as secretory expression. The GOX gene has been cloned in this study. This conclusion is based on the following: first, the ligated DNA determined by electrophoresis, was a 1489-1882bp fragment, close to the size of glucose oxidase (GOD), which is 1818bp. Secondly, the single open reading frame encoded a protein of 605 amino acids. Thirdly, secreted GOD recombinant proteins in the culture supernatants of the GOX gene transformant migrated as a single band in SDS-PAGE with an apparent molecular mass of between 75,000 and 100,000 Da, which is glycosylated GOD by the Pichia pastoris X-33 host machinery during the secretion process. Finally, the clones were cultured and secreted a protein, which possessed the GOD activity of catalyzing beta-d-glucose oxidation. With regard to the pH characteristics, the activity was more than 80% of the maximum activity in the range between pH 5 and pH 7. As for the temperature characteristics, the activity was not less than 92% of the maximum in the temperature range between 10 and 45 degrees C. The GOX gene transformant was able to maintain the GOD enzyme activity and produce recombinant GOD continuously for at least 2 weeks.

Immunogenicity of C-terminus of Plasmodium falciparum merozoite surface protein 1 expressed as a non-glycosylated polypeptide in yeast

The C-terminal region of the merozoite surface protein 1 (MSP119) is one of the most promising vaccine candidates against the erythrocytic forms of malaria. In the present study, a gene encoding Plasmodium falciparum MSP119 was expressed in yeast Pichia pastoris. A non-glycosylated form of the recombinant protein MSP119 was purified from culture medium. This recombinant protein maintains its antigenicity. Significant immune responses were seen in C57BL/6 mice after the second immunization. Moreover, the specific antibodies recognized the native antigens of P. falciparum. The prevailing isotypes of immunoglobulin (Ig) G associated with immunization were IgG1, IgG2a and IgG2b. The antibodies isolated from mouse sera immunized with MSP119 can inhibit parasite growth in vitro. Based on these immunological studies, we concluded that MSP119 deserves further evaluation in pre-clinical immunizations against P. falciparum.

Molecular cloning, sequencing, expression of Chinese sturgeon cystatin in yeast Pichia pastoris and its proteinase inhibitory activity

Cystatin, a superfamily of cysteine proteinase inhibitor of cathepsins and other cysteine proteinases, is widely distributed in animal tissues and body fluids. Although considerable attention has been given to mammalian and avian cystatins, little is known about cystatins from other vertebrates. In this study, a cDNA coding for Chinese sturgeon (Acipenser sinensis) cystatin was isolated and characterized. The corresponding mature cystatin peptide cDNA is 336 nucleotides long and encodes a protein of 112 amino acids. Sequence comparison showed that the cloned cystatin was a homolog of the mammalian Family II cystatin. The cystatin cDNA of Chinese sturgeon was subcloned into yeast expression vector pPICZalphaA and transformed into Pichia pastoris GS115 strain. After methanol induction, SDS-PAGE analysis of the culture supernatant indicated that the yield of recombinant cystatin was about 215 mg/l medium supernatant in shaking-flask fermentation medium, accounting for 73.6% of the total supernatant secreted proteins. Our data also showed that the recombinant cystatin is active in inhibiting the protease activity of papain and cathepsin B. Heat stability of the recombinant cystatin was also measured.

Extracellular production of human cystatin S and cystatin SA by Bacillus subtilis

We herein describe the development of a Bacillus subtilis system that can be used to produce large quantities of recombinant (r-) human salivary cystatins, a cysteine protease inhibitor of family 2 in the cystatin superfamily. The B. subtilis that lacked the alkaline protease E gene (DeltaaprE type mutant strain) was prepared by homologous recombination. The cDNA fragments coding for mature cystatins (S and SA) were ligated in frame to the DNA segment for the signal peptide of endoglucanase in the pHSP-US plasmid vector that was then use to transform the DeltaaprE type mutant strain of B. subtilis. The transformants carrying the expression vectors were cultivated in 5-L jar fermenters for 3 days at 30 degrees C. Both r-cystatin S and r-cystatin SA were successfully expressed and secreted into the culture broth, and were purified using a fast performance liquid chromatography system. The first use of DeltaaprE type mutant strain of B. subtilis made it possible to obtain a high yield of secreted protein, which makes this system an improvement over expression in Escherichia coli. We conclude that this system has high utility for expression of commercial quantities of secreted proteins.

Prevention of amyloid fibril formation of amyloidogenic chicken cystatin by site-specific glycosylation in yeast

To address the role of glycosylation on fibrillogenicity of amyloidogenic chicken cystatin, the consensus sequence for N-linked glycosylation (Asn106-Ile108 --> Asn106-Thr108) was introduced by site-directed mutagenesis into the wild-type and amyloidogenic chicken cystatins to construct the glycosylated form of chicken cystatins. Both the glycosylated and unglycosylated forms of wild-type and amyloidogenic mutant I66Q cystatin were expressed and secreted in a culture medium of yeast Pichia pastoris transformants. Comparison of the amount of insoluble aggregate, the secondary structure, and fibrillogenicity has shown that the N-linked glycosylation could prevent amyloid fibril formation of amyloidogenic chicken cystatin secreted in yeast cells without affecting its inhibitory activities. Further study showed this glycosylation could inhibit the formation of cystatin dimers. Therefore, our data strongly suggested that the mechanism causing the prevention of amyloidogenic cystation fibril formation may be realized through suppression of the formation of three-dimensional domain-swapped dimers and oligomers of amyloidogenic cystatin by the glycosylated chains at position 106.

Cloning, functional expression in Pichia pastoris, and purification of potato cystatin and multicystatin

In the tubers and leaves of potato, Solanum tuberosum, cysteine protease inhibitors are thought to play roles in the defence against herbivores and in regulating physiological processes like senescence and cell death. The cDNAs for two such inhibitors, potato multicystatin (PMC) with 8 cystatin domains and potato cystatin (PC) with a single domain, were cloned and expressed in the yeast Pichia pastoris. PC yielded on average 100 mg of purified active protein from 1l of culture supernatant. Purification to homogeneity was done in one step by cation exchange. The apparent equilibrium dissociation constant (K(i)) for papain was 0.1 nM. Cloning of the PMC cDNA was successful despite apparent toxicity for Escherichia coli and a high frequency of recombination events in RecA- strains of E. coli. In yeast, the expression of the cloned full length PMC gene was poor compared to that of the single domain.

Effect ofEPS1gene deletion inSaccharomyces cerevisiaeon the secretion of foreign proteins which have disulfide bridges

Both amyloid-prone cystatin and unstable mutant C94A lysozyme were secreted in wild-type and Deltaeps1 Saccharomyces cerevisiae cells. Amyloid-prone cystatin secreted at much higher level in Deltaeps1 cells than that in wild-type yeast. In parallel, the secretion amount of disulfide bond disrupted mutant C94A lysozyme greatly increased in Deltaeps1 cells although that was apparently low in wild-type yeast cells compared with the secretion amount of wild-type lysozyme. It is interesting that neither the unstable mutant C94A lysozyme nor amyloid-prone cystatin secreted in Deltaeps1 cells maintained their specific activities. These observations lead to the supposition that yeast cells deficient for the protein disulfide isomerase-family-member EPS1 locus secrete more of labile disulfide-containing model proteins.

Enhancement of proteinase inhibitory activity of recombinant human cystatin C using random-centroid optimization

We had previously written a random-centroid optimization computer program for genetics (RCG) to optimize protein engineering, which was successfully applied to modify single site of the 16 amino acid residues at the active site of B. stearothermophilys neutral protease for improving thermostability [J. Agric. Food Chem., 46 (1998) 1655]. The same program was applied in this study to double-site mutation of the entire sequence of human cystatin C (HCC) with 120 residues for improving its protease inhibitory activity. The RCG program selected two sites simultaneously and amino acid residues to replace the sites selected in the sequence in order to find the best papain-inhibitory activity and stability of the protease inhibitor. Twenty-three double mutants and twenty-two single mutants were expressed by Pichia pastoris. Of the total 45 mutants, G12W/H86V mutant showed a 5-fold increase in the bioactivity over the recombinant wild-type (WT) cystatin. Also, P13F mutant exhibited a half-life temperature (T1/2) 5.2 degrees C higher than 68.2 degrees C of WT in addition to a 56% greater papain inhibitory activity. Mutation for diminishing beta-sheet content reduced polymerization of cystatin C, thus improving papain-inhibitory activity. The approach using RCG was able to improve the functional properties of cystatin by least relying on the prior knowledge of its molecular structure.