O-mannosylation of recombinant human insulin-like growth factor I (IGF-I) produced in Saccharomyces cerevisiae

Engineering of the Saccharomyces cerevisiae yeast strain with multiple chromosome-integrated genes of human alpha-fetoprotein and its high-yield secretory production, purification, structural and functional characterization

Alpha-fetoprotein (AFP) is a biological drug candidate of high medicinal potential in the treatment of autoimmune diseases, cancer, and regenerative medicine. Large-scale production of recombinant human alpha-fetoprotein (rhAFP) is desirable for structural and functional studies and applied research. In this study we cloned and expressed in the secreted form wild-type glycosylated human rhAFP and non-glycosylated mutant rhAFP(0) (N233S) in the yeast strain Saccharomyces cerevisiae with multiple chromosome-integrated synthetic human AFP genes. RhAFP and rhAFP(0) were successfully produced and purified from the culture liquids active naturally folded proteins. Elimination of the glycosylation by mutation reduced rhAFP(0) secretion about threefold as compared to the wild-type protein showing critical role of the N-linked glycan for heterologous protein folding and secretion. Structural similarity of rhAFP and rhAFP(0) with natural embryonic eAFP was confirmed by circular dichroism technique. Functional tests demonstrated similar type of tumor suppressive and immunosuppressive activity for both recombinant species rhAFP and rhAFP(0) as compared to natural eAFP. It was documented that both types of biological activities attributed to rhAFP and rhAFP(0) are due to the fast induction of apoptosis in tumor cells and mitogen-activated lymphocytes. Despite the fact that rhAFP and rhAFP(0) demonstrated slightly less effective tumor suppressive activity as compared to eAFP but rhAFP(0) had produced statistically notable increase in its ability to induce inhibition of in vitro lymphocyte proliferation as compared to the glycosylated rhAFP and eAFP. We conclude that N-linked glycosylation of rhAFP is required for efficient folding and secretion. However the presence of N-linked sugar moiety was shown to be unimportant for tumor suppressive activity but was critically important for its immunoregulative activity which demonstrates that different molecular mechanisms are involved in these two types of biological functional activities attributed to AFP.

Production of native recombinant human midkine in the yeast, Pichia pastoris

Recombinant human midkine (rh-midkine) was efficiently produced in Pichia pastoris using the pre-pro secretion signal of yeast alpha-mating factor under the control of the AOX1 promoter. The pep4 host SMD1168 was used. The expression was induced at pH 3 and 20 degrees C in high cell-density fermentation and approximately 360 mg rh-midkine was secreted into 1L of medium. The authentic midkine could be obtained after one-step purification. Mass spectrometry of purified rh-midkine demonstrated a single large signal for the molecular ion [M + H](+) at 13241.2 m/z. This mass is identical to the authentic, unmodified human midkine. The precursor of rh-midkine was correctly processed in P. pastoris cells, yielding mature rh-midkine. Mass spectrometry detected no yeast-specific O-mannosylations in the purified midkine preparations. The circular dichroic spectrum indicated only a negative Cotton effect at 215 nm. Only beta-structures were indicated for the rh-midkine molecule in solution. Purified rh-midkine was active in a cell-proliferation assay.

Correct targeting of a vacuolar tobacco chitinase in Saccharomyces cerevisiae--post-translational modifications are dependent on the host strain

The chitinase gene FB7-1 of Nicotiana tabacum cv. samsun line 5 was expressed in the two Saccharomyces cerevisiae strains, INVSC2 and H4, under the control of the GAL1 promoter from S. cerevisiae and a multicopy plasmid vector. Both yeast strains express the plant gene as enzymatic active proteins. In transformants of the strain INVSC2, 94% of the total plant chitinase is contained inside the cells, probably within the vacuole which has been confirmed by subcellular fractionation as well as immunohistochemical experiments. This retention inside the cells is due to the C-terminally located 7 amino acids long vacuolar targeting peptide of the prochitinase. When this sequence was removed, chitinase was transported into the culture medium. Pulse-chase experiments revealed that during translation in transformants of both yeast strains one chitinase polypeptide can be immunoadsorbed with specific antibodies. In the case of INVSC2-transformants, newly formed chitinase is modified in a 60 min chase to slightly increase its molecular mass, whereas in H4-transformants the molecular mass constantly remained 32 kDa. By Western blot analysis two chitinase corresponding polypeptides of 32 and 37 kDa were accumulated in the culture medium of both transformants carrying the chitinase gene without the vacuolar targeting sequence. The larger one was very likely O-glycosylated. Whereas, both polypepitdes were also detected in cell extracts of the H4-transformant, only the smaller one was found in the INVSC2-transformant. The plant chitinase passed through the endoplasmic reticulum on its way to the vacuole. The N-terminal signal peptide responsible for the uptake into the endoplasmic reticulum is cleaved correctly. However, cleavage of the vacuolar targeting peptide located at the C-terminus, to give the mature chitinase is obviously influenced by the genetic background of the host strain. In INVSC2-transformants chitinase accumulates in its mature form whereas both the polypeptides of H4-transformants retain their vacuolar targeting peptide. Our results demonstrate that in the case of plant class I chitinase, the plant sorting signal is recognized in yeast cells but post-translational modifications are influenced by the host strain.

beta-Glucosylated proteins in the cell wall of the black yeast Exophiala (Wangiella) dermatitidis

Wild-type cells of the pathogenic black yeast Exophiala (Wangiella) dermatitidis grown in a low-pH ascorbate medium became less melanized and less resistant to Zymolyase. This was accompanied by increased staining with fluorescently labelled concanavalin A. The sugar composition of wild-type and mutant cell walls was, except for the presence of galactose, similar to that of Saccharomyces cerevisiae. Digestion of mutant cell walls with laminarinase released galactomannoproteins. In addition, the released cell wall proteins contained glucose and reacted with affinity-purified 1,6-beta-glucan antiserum, indicating that they are linked to 1,6-beta-glucan. It is proposed that 1,6-beta-glucosylated cell wall proteins generally occur among ascomycetes.

Recombinant technique and gonadotropins production: new era in reproductive medicine

OBJECTIVE

To review current knowledge regarding recombinant DNA technology and its safety and efficacy in relation to recombinant gonadotropin production.

DATA IDENTIFICATION AND SELECTION

Studies that relate specifically to recombinant DNA technology, method of laboratory production, and the clinical aspects of using recombinant gonadotropins were identified through literature and Medline searches.

RESULTS

Recent developments in recombinant DNA technology have resulted in a rapidly expanding range of new diagnostic and therapeutic opportunities. This technology paves the way to the identification, isolation, cloning, and production of specific proteins. Recently, recombinant human gonadotropins became available for clinical use. The pharmacokinetics, receptor availability, pharmacodynamics, and safety were studied extensively and the drugs were found to be identical if not superior to urinary gonadotropins that have been used in reproductive medicine for the last 30 years. It is clear today that the use of recombinant human gonadotropins is expected to provide better batch-to-batch consistency, steady supply, and most importantly, a purified compound with high specific activity, which accounts for >99% of the preparation's protein content, allowing SC administration.

CONCLUSION

There is no doubt that recombinant gonadotropins produced by genetic engineering technology are here to stay and will represent an important treatment modality in various fertility disturbances.

Secretion of a variant of human single-chain urokinase-type plasminogen activator without an N-glycosylation site in the methylotrophic yeast, Pichia pastoris and characterization of the secreted product

Human single-chain urokinase-type plasminogen activator without an N-glycosylation site (scu-PA-Q302) was produced in the methylotrophic yeast, Pichia pastoris using the shortened prepeptide sequence of a fungal aspartic proteinase, Mucor pusillus rennin (MPR). The level of urokinase-type plasminogen activator (u-PA) immunoreactive material in YPM medium was 0.47 mg/l; however, most of the secreted product had been processed to smaller polypeptides. The N-terminal amino acid sequence of major species was identical to that of the low molecular weight two-chain u-PA. Some approaches to minimizing the proteolysis of scu-PA-Q302 were attempted. Addition of Triton X-100, L-arginine and ammonium phosphate to the YPM medium minimized the proteolysis of scu-PA-Q302 and increased the yield of immunoreactive material to approximately 5 mg/l. Use of proteinase A- or proteinase B-deficient strains of yeast did not reduce the degradation. Co-expression of scu-PA-Q302 and urinary trypsin inhibitor resulted in partial reduction of the major species of proteolysis. Scu-PA-Q302 was purified from the culture supernatant of the improved medium by two successive chromatographies on Phenyl-Sepharose and S-Sepharose. The purified protein had a molecular weight of 47 kDa. It did not contain detectable N-linked oligosaccharides, but contained O-linked oligosaccharides attached to the light chain. N-terminal amino acid sequencing of the purified preparation showed that the shortened prepeptide sequence of MPR was correctly processed by the Pichia yeast. Scu-PA-Q302 closely resembles natural scu-PA with respect to its enzymatic activity against the chromogenic substrate S-2444 and its in vitro fibrinolytic properties.

O-glycosylation of the Thr70 residue of cell-adhesive lysozyme in yeast

The cell-adhesive protein Cys-RGD4 has been constructed using a yeast expression system by inserting the sequence Cys-Arg-Gly-Asp-Ser-Cys (CRGDSC) between Val74 and Asn75 of human lysozyme [Yamada, T., Uyeda, A., Kidera, A. & Kikuchi, M. (1994b) Biochemistry 33, 11678-11683]. The Cys74a, Arg74b, Gly74c, Asp74d, Ser74e, Cys74f-lysozyme mutant, purified from the yeast culture supernatant contained glycosylated variants, in addition to the unglycosylated form. Peptide mapping analyses suggested that the glycosylation occurred at the Thr70 residue in the Cys-RGD4 molecule. Electrospray ionization mass spectrometric analysis demonstrated the presence of two hexose residues in the major variant, and one, three, four, or five hexose residues in the minor variants. All of these hexose residues were identified as mannose by analysis of the oligosaccharide mixture obtained by mild alkaline treatment of the variants. No other glycosylation was observed, although the Cys-RGD4 molecule possesses a total of 12 threonine and serine residues. In addition, the Thr70 residue is not glycosylated in either native lysozyme or the Arg-Gly-Asp-Ser (RGDS)-inserted mutant, RGD4 [Yamada, T., Matsushima, M., Inaka, K., Ohkubo, T., Uyeda, A., Maeda, T., Titani, K., Sekiguchi, K. & Kikuchi, M. (1993) J. Biol. Chem. 268, 10588-10592]. Thus, this O-glycosylation seems to be specific for both the mutant lysozyme molecule and the site of the threonine residue. Structural analyses of these lysozymes by X-ray crystallography suggest that the conformation of the serine-containing or threonine-containing region can affect the specificity of yeast O-glycosylation.

[Effect of changes in the lipid composition on the plasma membrane of Saccharomyces cerevisiae through mutation of the phase transition and mixing behavior of the lipid fraction]

Mutation of Saccharomyces cerevisiae leads to an alteration of the size and surface structure of the mutant cell. These phenomena are correlated with change in the lipid composition and hence membrane fluidity of the plasma membranes. Such alterations are in the fatty acyl constituents of phospholipids and glycolipids and include changes in the saturation or length of fatty acyl chains. Simultaneously, the "melting point" of phospholipid fractions, i.e. the temperature of the ordered-disordered phase transition and mixing behavior, changed. Consequently calorimetry on isolated phospholipid fractions extracted from plasma membranes is a useful analytical method to demonstrate directly such phase transitions and change in the mixing behavior of the cellular lipid fractions in connection with mutation. A correlation between the alteration of the lipid composition in the plasma membrane of strains of S. cerevisiae S 288 and its mutant VY 1160 is discussed.

Analysis of protein glycosylation by mass spectrometry

There is a growing pharmaceutical market for protein-based drugs for use in therapy and diagnosis. The rapid developments in molecular and cell biology have resulted in production of expression systems for manufacturing of recombinant proteins and monoclonal antibodies. These proteins are glycosylated when expressed in cell systems with glycosylation ability. For glycoproteins intended for therapeutic administration it is important to have knowledge about the structure of the carbohydrate side chains to avoid cell systems that produce structures, which in humans can cause undesired reactions, e.g., immunological and unfavorable serum clearance rate. Structural analysis of glycoprotein oligosaccharides requires sophisticated instruments like mass spectrometers and nuclear magnetic resonance spectrometers. However, before the structural analysis can be conducted, the carbohydrate chains have to be released from the protein and purified to homogeneity, and this is often the most time-consuming step. Mass spectrometry has played and still plays an important role in analysis of protein glycosylation. The superior sensitivity compared to other spectroscopic methods is its main asset. Structural analysis of carbohydrates faces several problems, however, due to the chemical nature of the constituent monosaccharide residues. For oligosaccharides or glycoconjugates, the structural information from mass spectrometry is essentially limited to monosaccharide sequence, molecular weight, an only in exceptional cases glycosidic linkage positions can be obtained. In order to completely establish an oligosaccharide structure, several other structural parameters have to be determined, e.g., linkage positions, anomeric configuration and identification of the monosaccharide building blocks. One way to address some of these problems is to work on chemical pretreatment of the glycoconjugate, to specifically modify the carbohydrate chain. In order to introduce specific modifications, we have used periodate oxidation and trifluoroacetolysis with the objective of determining glycosidic linkage positions by mass spectrometry.

The carbohydrate chains of the beta subunit of human chorionic gonadotropin produced by the choriocarcinoma cell line BeWo. Novel O-linked and novel bisecting-GlcNAc-containing N-linked carbohydrates

The N-linked carbohydrate chains of the beta subunit of human chorionic gonadotropin (hCG-beta) isolated from the culture fluid of the choriocarcinoma cell line BeWo were released enzymatically by peptide-N4-(N-acetyl-beta-glucosaminyl)asparagine amidase F. Subsequently, the O-linked oligosaccharides were split off from the N-deglycosylated protein by mild alkaline borohydride treatment. The carbohydrate chains were purified in their intact sialylated forms by FPLC anion-exchange chromatography on Mono Q, HPLC on Lichrosorb-NH2, and high-pH anion-exchange chromatography on CarboPac PA1. 1H-NMR spectroscopic analysis of the major fractions demonstrates the occurrence of the following sialylated diantennary and triantennary N-linked oligosaccharides. Residues not written in bold letters are variably present. [formula: see text] The incidence of triantennary carbohydrate chains is much higher than in normal urinary hCG-beta (26% vs 2%). The same holds for the alpha 1-6-fucosylation of the asparagine-bound GlcNAc (95% vs 42%). The presence of a bisecting GlcNAc and the occurrence of alpha 2-6-linked Neu5Ac in the most abundant N-glycans, are new features for hCG-beta. The major O-linked carbohydrate chains identified are the tetrasaccharide Neu5Ac alpha 2-3Gal beta 1-3(Neu5Ac alpha 2-6)GalNAc-ol and the hexasaccharide Neu5Ac alpha 2-3Gal beta 1-4GlcNAc beta 1-6(Neu5Ac alpha 2-3Gal beta 1-3)GalNAc-ol, both also found in normal urinary hCG. In addition, two novel O-glycans were characterized: [formula: see text]

The Oligosaccharides of Glycoproteins: Bioprocess Factors Affecting Oligosaccharide Structure and their Effect on Glycoprotein Properties

In this review, we organize the recent data concerning the effects of bioprocess factors on the oligosaccharide structure of human therapeutic glycoproteins, with particular emphasis on the influence of the host cell. We also discuss the effect of oligosaccharide structure on glycoprotein properties, including antigenicity, immunogenicity and plasma clearance rate.

Isolation and structure determination of the intact sialylated N-linked carbohydrate chains of recombinant human follitropin expressed in Chinese hamster ovary cells

Biologically active recombinant human follitropin has been expressed in Chinese hamster ovary cells. The carbohydrate chains of the recombinant glycoprotein hormone were enzymatically released by peptide-N4-(N-acetyl-beta-glucosaminyl)asparagine amidase F. The oligosaccharides were separated from the N-deglycosylated protein by gel-permeation chromatography on Bio-Gel P-100, and fractionated by a combination of FPLC on Mono Q and HPLC on Lichrosorb-NH2. The structures of the carbohydrate chains were determined by 500- or 600-MHz 1H-NMR spectroscopy. The following types of carbohydrates occur: monosialylated diantennary (10%), disialylated diantennary (43%), disialylated tri-antennary (5%), trisialylated tri-antennary (13%), trisialylated tri'-antennary (8%), and tetrasialylated tetraantennary (12%) N-acetyllactosamine type of carbohydrate chains, all bearing exclusively alpha 2-3-linked N-acetylneuraminic acid (Neu5Ac). Previously, for pituitary follitropin mono-, di-, tri-, tri'-, and tetra-antennary oligosaccharides containing alpha 2-3- as well as alpha 2-6-linked Neu5Ac residues were reported. The bisecting GlcNAc residues present in native follitropin were not detected in the recombinant glycoprotein. Of the oligosaccharides 29% have an alpha 1-6-linked Fuc residue at the asparagine-bound GlcNAc, whereas this amount is about 50% in pituitary follitropin. In some of the tri-, tri'- and tetra-antennary oligosaccharide fractions small amounts (less than 5%) of compounds were detected having one or more additional N-acetyllactosamine units.