Oral immunization with whole yeast producing viral capsid antigen provokes a stronger humoral immune response than purified viral capsid antigen

Weak antibody responses to protein antigens after oral immunization remain a serious problem. Yeasts have a rigid cell wall and are inherently resistant to harsh conditions, suggesting that recombinant antigens made in yeast could have a greater chance of making contact with the immune cells of the gastrointestinal (GI) tract in intact form. We compared antibody responses to oral immunization with purified recombinant antigen, used in the conventional manner, and responses to whole recombinant yeast producing the antigen intracellularly. Recombinant capsid protein (CP) of red-spotted grouper necrosis virus (RGNNV) was used as model antigen and Saccharomyces cerevisiae as host. The purified CP was obtained from the S. cerevisiae producing the RGNNV CP. Whole recombinant yeast producing RGNNV CP provoked 9-27 times higher anti-RGNNV CP IgG titres than purified RGNNV CP. Moreover, sera from mice immunized with the recombinant yeast had neutralizing activity against RGNNV, while those from mice immunized with purified CP did not. These results show that whole recombinant yeast is a promising platform for antigen delivery by oral immunization.

SIGNIFICANCE AND IMPACT OF THE STUDY

Provoking sufficient antibody responses by oral immunization has been an enormous challenge because of the harsh conditions of the gastrointestinal (GI) tract. Immunization strategies using purified antigen to make oral vaccines are incapable of commercialization because excessive amount of antigen is required to provoke antibody responses. Therefore, resolving the problems concerning the cost and effectiveness of oral vaccines is a high priority. Our results suggest that recombinant yeast has great potential for inducing antigen-specific immune responses by oral immunization. We believe that oral immunization using recombinant yeast can be a breakthrough technology.

Cloning and functional analysis of the GSH1/MET1 gene complementing cysteine and glutathione auxotrophy of the methylotrophic yeast Hansenula polymorpha

The Hansenula polymorpha GSH1/MET1 gene was cloned by complementation of glutathione-dependent growth of H. polymorpha gsh1 mutant isolated previously as N-methyl-N'-nitro-N-nitrosoguanidine (MNNG) resistant and cadmium ion sensitive clone. The H. polymorpha GSH1 gene was capable of restoring cadmium ion resistance, MNNG sensitivity, normal glutathione level and cell proliferation on minimal media without addition of cysteine or glutathione, when introduced into the gsh1 mutant cells. It was shown that the H. polymorpha GSH1 gene has homology to the Saccharomyces cerevisiae MET1 gene encoding S-adenosyl-L-methionine uroporphyrinogen III transmethylase, responsible for the biosynthesis of sulfite reductase cofactor, sirohaem. The H. polymorpha GSH1/MET1 gene deletion cassette (Hpgsh1/met1::ScLEU2) was constructed and corresponding null mutants were isolated. Crossing data of the point gsh1 and null gsh1/met1 mutants demonstrated that both alleles were located to the same gene. The null gsh1/met1 mutant showed total growth restoration on minimal media supplemented with cysteine or glutathione as a sole sulfur source, but not with inorganic (sulfate, sulfite) or organic (methionine, S-adenosylmethionine) sources of sulfur. Moreover, both the point gsh1 and null gsh1/met1 mutants displayed increased sensitivity to the toxic carbon substrate methanol, formaldehyde, organic peroxide and cadmium ions.

Inactivation of the Hansenula polymorpha PMR1 gene affects cell viability and functioning of the secretory pathway

In yeast, functions of the endoplasmic reticulum (ER) depend on the Golgi apparatus Ca2+ pool, which is replenished by the medial-Golgi ion pump Pmr1p. Here, to dissect the role of the Golgi Ca2+ pool in protein folding and elimination of unfolded proteins in the ER, the manifestations of the pmr1 mutation in yeast Hansenula polymorpha were studied. The PMR1 gene was disrupted in a H. polymorpha diploid strain. Haploid segregants of this diploid bearing the disruption allele were viable, though they showed a severe growth defect on synthetic medium and rapidly died during storage at low temperature. Disruption of H. polymorpha PMR1 led to defects of the Golgi-hosted protein glycosylation and vacuolar protein sorting. This mutation increased the survival rate of H. polymorpha cells upon treatment with the proapoptotic drug amiodarone. Unlike Saccharomyces cerevisiae, the H. polymorpha pmr1 mutant was not hypersensitive to chemicals that induce the accumulation of unfolded proteins in the ER, indicating that the elimination of unfolded proteins from the ER was not essentially affected. At the same time, the pmr1 mutation improved the secretion of human urokinase and decreased its intracellular aggregation, indicating an influence of the mutation on the protein folding in the ER.

Pharmacokinetics and bioequivalence evaluation of two gabapentin preparations after a single oral dose in healthy Korean volunteers

OBJECTIVE

To evaluate the bioequivalence of a single oral 400 mg dose of 2 gabapentin preparations in healthy male Korean volunteers.

SUBJECTS, MATERIALS AND METHODS

The study was conducted as a randomized, 2-period crossover design in 26 healthy male Korean volunteers who received a single oral dose of 400 mg gabapentin capsule in each study period. There was a 7-day washout period between the doses. Serum concentrations of gabapentin up to 24 hours after the administration were determined using a validated HPLC method with fluorescence detection. In addition, in vitro dissolution profiles of both preparations were examined. The pharmacokinetic parameters such as AUC(0.t) (the area under the curve from zero to the time), AUC(0-infinity) (the area under the curve from zero to infinity), C(max) (maximum serum concentration), t(max) (time to reach C(max)) and t1/2 (terminal half-life) were analyzed by noncompartmental analysis, and the analysis of variance (ANOVA) was carried out using logarithmically transformed AUC(0-t), AUC(0-infinity) and C(max) and untransformed t(max).

RESULTS

In vitro dissolution profiles were very similar at all media. There were no significant differences between the two preparations in AUC(0-t), AUC(0-infinity) and C(max). The point estimates (90% confidence intervals) for AUC(0-t), AUC(0-infinity) and C(max) were 1.0319 (0.9142 - 1.1647), 1.0127 (0.8458 - 1.2127) and 0.9796 (0.8670 - 1.1069), respectively, satisfying the bioequivalence criteria of 0.80 - 1.25 as proposed by the US FDA and the Korean legislation. No statistically significant difference was found for tmax and t1/2 values.

CONCLUSION

From the results of the present study, it is indicated that the two preparations of gabapentin are bioequivalent and it can be assumed that they are therapeutically equivalent and exchangeable in clinical practice.

Cloning and expression of a novel esterase gene cpoA from Burkholderia cepacia

AIMS

To screen and clone a novel enzyme with specific activity for the resolution of (R)-beta-acetylmercaptoisobutyrate (RAM) from (R,S)-beta-acetylmercaptoisobutyrate [(R,S)-ester].

METHODS AND RESULTS

A micro-organism that produces a novel esterase was isolated and identified as the bacterium Burkholderia cepacia by using the analysis of cellular fatty acids, Biolog automated microbial identification/characterization system, and 16S rRNA gene sequence analysis. A novel esterase gene was cloned from the chromosomal DNA of B. cepacia and was designated as cpoA. The cpoA encodes a polypeptide of 273 amino acids which shows a strong sequence homology with many bacterial nonhaeme chloroperoxidases. In addition, a typical serine-hydrolase motif, Gly-X-Ser-X-Gly, and the highly conserved catalytic triad, Ser95, Asp224, and His253, were identified in the deduced amino acid sequence of cpoA by multiple sequence alignment.

CONCLUSION

The cpoA cloned from B. cepacia encodes a novel esterase which is highly related to the nonhaeme chloroperoxidases.

SIGNIFICANCE AND IMPACT OF THE STUDY

This is the first report that describes the isolation and cloning of a serine esterase gene from B. cepacia, which is useful in the chiral resolution of (R,S)-ester. The cloned gene will allow additional research on the bifunctionality of the enzyme with esterase and chloroperoxidase activity at the structural and functional levels.

Independent Exponential Feeding of Glycerol and Methanol for Fed-Batch Culture of Recombinant Hansenula polymorpha DL-1

As a novel feeding strategy for optimizing human epidermal growth factor (hEGF) production with a recombinant Hansenula polymorpha DL-1 using the methanol oxidase (MOX) promoter in H. polymorpha DL-1, independent exponential feeding of two substrates was used. A simple kinetic model considering the cell growth on two substrates was established and used to calculate the respective feeding rates of glycerol and methanol. In the fedbatch culture with methanol-only feeding, the optimal set point of specific growth rate on methanol was found to be 0.10 h-1. When the fed-batch cultures were conducted by the independent feeding of glycerol and methanol, the actual specific growth rate on glycerol and methanol was slightly lower than the set point of specific growth rate. By the uncoupled feeding of glycerol and methanol the volumetric productivity of hEGF increased from 6.4 to 8.0 mg/(L.h), compared with methanol-only feeding.

Current status of the anticoagulant hirudin: its biotechnological production and clinical practice

Hirudin is a potent thrombin inhibitor originally derived from the medicinal leech, Hirudo medicinalis. Owing to its high affinity and specificity for thrombin, hirudin has been intensively investigated for research and therapeutic purposes. The investigation of hirudin has contributed greatly to the understanding of the mode of action of thrombin and the clotting system. Hirudin and several hirudin analogues have also been demonstrated to have several advantages as a highly specific anticoagulant over the most widely used drug, heparin. Due to the great demand for hirudin in physicochemical and clinical studies, various recombinant systems have been developed, using bacteria, yeasts, and higher eukaryotes, to obtain the biologically active hirudin in significant quantities. After 10 years of clinical applications, two recombinant hirudins and a hirudin analogue have gained marketing approval from the United States Food and Drug Administration, for several applications. Clinical trials are currently ongoing for other treatments for thrombotic disease. As a consequence, it is conceivable that hirudin may expand its therapeutic utility over heparin in the near future.

Development of expression systems for the production of recombinant human serum albumin using the MOX promoter in Hansenula polymorpha DL-1

To optimize the secretory expression of recombinant human serum albumin (HSA) under the control of methanol oxidase (MOX) promoter in the methylotrophic yeast Hansenula polymorpha DL-1, we analyzed several parameters affecting the expression of HSA from the MOX promoter. Removal of the 5'-untranslated region derived from HSA cDNA in the expression cassette led to at least a fivefold improvement of HSA expression efficiency at the translational level. With the optimized expression cassette, the gene dosage effect on HSA expression was abolished and thus, a single copy of the expression vector integrated into the MOX locus became sufficient for the maximal expression of HSA. Northern blot analysis revealed that the levels of HSA transcript did not increase any further upon increasing copy number. The mox-disrupted (mox Delta) transformant was constructed, in which the genomic MOX gene was transplaced with the HSA expression cassette, to examine the effect of the methanol oxidase-deficient phenotype of the host on HSA expression. The mox Delta transformant showed higher levels of HSA production in shake-flask cultures than the MOX wild-type transformant, especially at low concentrations of methanol and a twofold higher specific HSA production rate in fed-batch fermentation with an abrupt induction mode. The native prepro signal sequence of HSA secreted in H. polymorpha was correctly processed and the mature recombinant protein had a pI value identical to that of the authentic HSA. Our results suggest that the H. polymorpha expression systems developed in this study are suitable for large-scale production of recombinant albumin.

Effects of methanol on expression of an anticoagulant hirudin in recombinant Hansenula polymorpha

A series of batch, fed-batch, and continuous cultures was carried out to analyze the effects of methanol on the fermentation characteristics of recombinant Hansenula polymorpha for the production of hirudin, an anticoagulant. Hirudin expression efficiencies were greatly influenced by the methanol concentrations in continuous and fed-batch culture modes. At a steady state of continuous culture, an optimum methanol concentration of 1.7 g l(-1) was determined at a dilution rate of 0.18 h(-1) with 1.8 mg l(-1) h(-1) hirudin productivity.

Molecular characterization of the actin-encoding gene and the use of its promoter for a dominant selection system in the methylotrophic yeast Hansenula polymorpha

The actin gene (ACT) from the methylotrophic yeast Hansenula polymorpha was cloned and its structural feature was characterized. In contrast to the actin genes of other ascomycetous yeasts, which have only one large intron, the H. polymorpha ACT gene was found to be split by two introns. The H. polymorpha ACT introns were correctly processed in the heterologous host Saccharomyces cerevisiae despite appreciable differences in the splice site sequences. The promoter region of H. polymorpha ACT displayed two CCAAT motifs and two TATA-like sequences in a configuration similar to that observed in the S. cerevisiae actin promoter. A set of deleted H. polymorpha ACT promoters was exploited to direct expression of the bacterial hygromycin B resistance (hph) gene as a dominant selectable marker in the transformation of H. polymorpha. The resistance level of H. polymorpha transformants to the antibiotic was shown to be dependent on the integration copy number of the hph cassette. The selectivity of the hygromycin B resistance marker for transformants of higher copy number was remarkably increased with the deletion of the upstream TATA-like sequence, but not with the removal of either CCAAT motif, from the H. polymorpha promoter. The dosage-dependent selection system developed in this study should be useful for genetic manipulation of H. polymorpha as an industrial strain to produce recombinant proteins.

Cloning of the Aspergillus niger pmrA gene, a homologue of yeast PMR1, and characterization of a pmrA null mutant

The pmrA gene, a yeast PMR1 homologue, was isolated from Aspergillus niger. Sequence analysis of the pmrA cDNA and the genomic DNA revealed that two introns exist in the coding region, and that an open reading frame in the cDNA encodes a polypeptide of 1056 amino acids containing all the conserved regions present in P-type Ca2+-ATPases. The predicted pmrA protein exhibited a high degree of sequence similarity to the Pmr1 proteins from yeasts and mammalians (50-59% identity). The expression of the pmrA cDNA partially restored the growth defect of Yarrowia lipolytica pmr1 null mutant on EGTA-containing medium. This indicates that the A. niger pmrA gene encodes a functional homologue of the yeast P-type Ca2+-ATPase involved in the secretory pathway. An A. niger pmrA null mutant exhibited growth retardation on EGTA-containing medium and the growth defect was overcome by adding Ca2+ or Mn2+ into the medium. This suggests an involvement of the pmrA protein in Ca2+ and Mn2+ homeostasis in A. niger.

Cloning and characterization of the Hansenula polymorpha homologue of the Saccharomyces cerevisiae MNN9 gene

A gene homologous to Saccharomyces cerevisiae MNN9 has been cloned and characterized in the methylotrophic yeast Hansenula polymorpha. This gene was cloned from a H. polymorpha genomic DNA library using the S. cerevisiae MNN9 gene as a probe. The H. polymorpha MNN9 homologue (HpMNN9) contained a 1062 bp open reading frame encoding a predicted protein of 354 amino acids. The deduced amino acid sequence showed 58% and 51% identity, respectively, with the S. cerevisiae and Candida albicans Mnn9 proteins. Disruption of HpMNN9 leads to phenotypic effects suggestive of cell wall defects, including detergent sensitivity and hygromycin B sensitivity. The hygromycin B sensitivity of S. cerevisiae mnn9 null mutant was complemented in the presence of the HpMNN9 gene. The DNA sequence of the H. polymorpha homologue has been submitted to GenBank with the Accession No. AF264786.

Temporary tattooing followed by Q-switched alexandrite laser for treatment of syringomas

BACKGROUND

Syringomas usually develop in women as multiple skin-colored papules primarily seen on the periocular regions and cheeks. They can cause cosmetic problems and lead to poor self-esteem. Though several treatment modalities have been established, such as excision, electro/cryosurgery, chemical peeling, and CO2 laser surgery, none of them are satisfactory due to their limitations and side effects, for example, pain, prolonged healing time, postoperative erythema/pigmentary changes, and scarring.

OBJECTIVE

The objective of this study was to develop a new treatment method for syringoma and to minimize the side effects through selective destruction of the tumor.

METHODS

Six patients with multiple periorbital syringomas were enrolled in this study. The surface epithelium of the syringomas was vaporized by CO2 laser, and black ink was introduced in order to allow penetration to the dermis using iontophoresis. Subsequently the artificial tattoos were removed by Q-switched alexandrite laser. The results were evaluated clinically by both physicians and patients at 1, 2, 4, and 8 weeks after treatment.

RESULTS

The majority of syringoma in the six patients disappeared by the first follow-up 1 week after treatment. There were no cases of prolonged erythema persisting beyond 2 weeks. Additional treatment was repeated in the same manner in order to remove the remaining syringomas in one patient. There were no recurrences during the 8-week follow-up period.

CONCLUSION

Our new treatment was safer, less painful, nonscarring, and there was a quicker recovery period and less of a burden to repeat treatment when necessary.

Proteolytic stability of recombinant human serum albumin secreted in the yeast Saccharomyces cerevisiae

In order to direct the persistent expression of recombinant human serum albumin (HSA) from the GAL10 promoter in the yeast Saccharomyces cerevisiae, we carried out periodic feeding of galactose during shake-flask cultures. Unexpectedly, the recombinant protein secreted was observed to undergo rapid degradation, which was apparently accelerated by carbon-source feeding. The extracellular degradation of HSA occurred even in the strain deficient in the major vacuolar proteases PrA and PrB, and in the strain lacking the acidic protease Yap3p (involved in the generation of HSA-truncated fragments). Interestingly, the degradation correlated closely with the acidification of extracellular pH and thus was significantly overcome either by buffering the culture medium above pH 5.0 or by adding amino acid-rich supplements to the culture medium, which could prevent the acidification of medium pH during cultivation. Addition of arginine or ammonium salt also substantially minimized the degradation of HSA, even without buffering. The extracellular degradation activity was not detected in the cell-free culture supernatant but was found to be associated with intact cells. The results of the present study strongly suggest that the HSA secreted in S. cerevisiae is highly susceptible to the pH-dependent proteolysis mediated by cell-bound protease(s) whose activity and expression are greatly affected by the composition of the medium.

Improvement of intact human lipocortin-I production in Saccharomyces cerevisiae by inhibiting proteolysis

Human lipocortin-I (hLC1), when was expressed as a secretory product in Saccharomyces cerevisiae, was cleaved to a significant extent by endoproteolytic processing, resulting in the accumulation of des1-26-hLC1 in the culture supernatant. This proteolytic cleavage was inhibited significantly by the addition of high concentrations of l-arginine and l-lysine, with a resultant marked improvement in the yield of intact hLC1. When the hLC1 was expressed in S. cerevisiae mutants deficient in one or two of the following endoproteases, Kex2p, Mkc7p and Yps1p (Yap3p), the mutants exhibited no reduction in the extent of hLC1 proteolysis, indicating that these endoproteases are not involved in the proteolytic cleavage of hLC1.

The comparative molecular study between Bombycidae and Saturniidae based on mtDNA RFLP and cytochrome oxidase I gene sequences: implication for molecular evolution

The phylogenetic relationships between Bombyx mori and Bombyx mandarina species of Bombycidae, and Antheraea yamamai and Antheraea pernyi species of Saturniidae were investigated based on mtDNA RFLP and cytochrome oxidase I gene. The sizes of the mtDNA of all the species were estimated at approximately 16 kbp +/- 500 bp by total length of all the restricted fragments and no variation in size was recognized. Of the fourteen different restriction endonucleases used, BamHI, HindIII, PstI, EcoRI and XbaI showed RFLP. Among these, only HindIII showed RFLP between B. mori and B. mandarina. A comparative analysis of sequences was also conducted with the mitochondrial cytochrome oxidase I genes of each species. The results indicated that B. mori shared a 97%, 85% and 87% sequence identity with B. mandarina, A. yamamai and A. pernyi, respectively. B. mandarina shared a 87% and 88% sequence identity with A. yamamai and A. pernyi, respectively. A. yamamai shared 92% sequence identity with A. pernyi. The results of the phylogenetic analysis exhibited monophyly and confidence limits of more than 99% in all trees for both Bombycidae and Saturniidae.

A dominant selection system designed for copy-number-controlled gene integration in Hansenula polymorpha DL-1

To facilitate the selection of multiple gene integrants in Hansenula polymorpha, a rapid and copy-number-controlled selection system was developed using a vector containing a telomeric autonomous replication sequence and the bacterial aminoglycoside 3-phosphotransferase (APH) gene. Direct use of the unmodified APH gene as a dominant selectable marker resulted in the extremely slow growth of transformants and the frequent selection of spontaneous resistance. For the proper performance of the APH gene, a set of deleted glyceraldehyde-3-phosphate dehydrogenase (GAPDH) promoters of H. polymorpha were fused to the APH gene. The fusion construct with the 578-bp GAPDH promoter conferred G418 resistance sufficient to allow rapid growth of transformants, and thus facilitated the selection of transformants with up to 15 tandem copies of the vector. To increase further the integration copy number within the gene-dose-dependent range, the GAPDH promoter was serially deleted down to the -61 nucleotide. With this weak expression cassette, the integration copy number could easily be controlled between 1 and 50. Tandemly integrated copies of plasmids near the end of the chromosome were mitotically stable over 150 generations. The dosage-dependent selection system of this study would provide a powerful tool for the development of H. polymorpha as an industrial strain to produce recombinant proteins.

A family of telomere-associated autonomously replicating sequences and their functions in targeted recombination in Hansenula polymorpha DL-1

A family of multiple autonomously replicating sequences (ARSs) which are located at several chromosomal ends of Hansenula polymorpha DL-1 has been identified and characterized. Genomic Southern blotting with an ARS, HARS36, originating from the end of a chromosome, as a probe showed several homologues in the genome of H. polymorpha. Nucleotide sequences of the three fragments obtained by a selective cloning for chromosomal ends were nearly identical to that of HARS36. All three fragments harbored an ARS motif and ended with 18 to 23 identical repetitions of 5'-GGGTGGCG-3' which resemble the telomeric repeat sequence in other eukaryotes. Transformation of H. polymorpha with nonlinearized plasmids containing the newly obtained telomeric ARSs almost exclusively resulted in the targeted integration of a single copy or multiple tandem copies of the plasmid into the chromosomes. The sensitivity to exonuclease Bal31 digestion of the common DNA fragment in all integrants confirmed the telomeric origin of HARS36 homologues, suggesting that several chromosomal ends, if not all of them, consisted of the same ARS motif and highly conserved sequences observed in HARS36. Even though the frequencies of targeted recombination were varied among the ends of the chromosomes, the overall frequency was over 96%. The results suggested that the integration of the plasmids containing telemeric ARSs occurred largely through homologous recombination at the telomeric repeats, which serve as high-frequency recombination targets.

Cloning and characterization of the Hansenula polymorpha homologue of the Saccharomyces cerevisiae PMR1 gene

A gene homologous to Saccharomyces cerevisiae PMR1 has been cloned in the methylotrophic yeast Hansenula polymorpha. The partial DNA fragment of the H. polymorpha homologue was initially obtained by a polymerase chain reaction and used to isolate the entire gene which encodes a protein of 918 amino acids. The putative gene product contains all ten of the conserved regions observed in P-type ATPase. The cloned gene product exhibits 60.3% amino acid identity to the S. cerevisiae PMR1 gene product and complemented the growth defect of a S. cerevisiae pmr1 null mutant in the EGTA-containing medium. The results demonstrate that the H. polymorpha gene encodes the functional homologue of the S. cerevesiae PMR1 gene product, a P-type Ca(2+)-ATPase.

Efficient production of intact human parathyroid hormone in a Saccharomyces cerevisiae mutant deficient in yeast aspartic protease 3 (YAP3)

When human parathyroid hormone (hPTH) is expressed as a secretory product in yeast, the main problem is the aberrant proteolytic cleavage that reduces the yield of intact protein. To overcome this problem, we developed an hPTH expression system using a host strain in which the YAP3 gene encoding yeast aspartic protease 3 (YAP3) was disrupted. After 48 h of culture, most of the hPTH secreted by the yap3 disruptant remained intact, whereas more than 90% of the hPTH secreted by the wild-type strain was cleaved. When the authentic hPTH was incubated in each of the culture supernatants of untransformed yap3 disruptant and wild-type strain, the proteolysis proceeded much more slowly in the culture supernatant of yap3 disruptant than in that of the wild type. The extent of hPTH proteolysis was also significantly reduced by the addition of pepstatin A, a specific aspartic protease inhibitor. The results suggest that YAP3 is involved in the internal cleavage of hPTH expressed in yeast. The correct processing of the intact hPTH secreted in the yap3 disruptant demonstrates that the yeast mutant lacking the YAP3 activity is a suitable host for the high-level expression of intact hPTH.

Glycosylation of human alpha 1-antitrypsin in Saccharomyces cerevisiae and methylotrophic yeasts

Human alpha 1-antitrypsin (alpha 1-AT) is a major serine protease inhibitor in plasma, secreted as a glycoprotein with a complex type of carbohydrate at three asparagine residues. To study glycosylation of heterologous proteins in yeast, we investigated the glycosylation pattern of the human alpha 1-AT secreted in the baker's yeast Saccharomyces cerevisiae and in the methylotrophic yeasts, Hansenula polymorpha and Pichia pastoris. The partial digestion of the recombinant alpha 1-AT with endoglycosidase H and the expression in the mnn9 deletion mutant of S. cerevisiae showed that the recombinant alpha 1-AT secreted in S. cerevisiae was heterogeneous, consisting of molecules containing core carbohydrates on either two or all three asparagine residues. Besides the core carbohydrates, variable numbers of mannose outer chains were also added to some of the secreted alpha 1-AT. The human alpha 1-AT secreted in both methylotrophic yeasts was also heterogeneous and hypermannosylated as observed in S. cerevisiae, although the overall length of mannose outer chains of alpha 1-AT in the methylotrophic yeasts appeared to be relatively shorter than those of alpha 1-AT in S. cerevisiae. The alpha 1-AT secreted from both methylotrophic yeasts retained its biological activity as an elastase inhibitor comparable to that of alpha 1-AT from S. cerevisiae, suggesting that the different glycosylation profile does not affect the in vitro activity of the protein.

Folding and stability of the Z and S(iiyama) genetic variants of human alpha1-antitrypsin

Z (Glu342 --> Lys) and S(iiyama) (Ser53 --> Phe) genetic variations of human alpha1-antitrypsin (alpha1-AT) cause a secretion blockage in the hepatocytes, leading to alpha1-AT deficiency in the plasma. Using in vitro folding analysis, we have shown previously that these mutations interfere with the proper folding of polypeptides. To understand the fundamental cause for the secretion defect of the Z and S(iiyama) variants of alpha1-AT, we investigated in vivo folding and stability of these variant alpha1-AT using the secretion system of yeast Saccharomyces cerevisiae. Various thermostable mutations suppressing the folding block of the Z variant in vitro corrected the secretion defect as well as the intracellular degradation in the yeast secretion system. Significantly, the extent of suppression in the secretion defect of Z protein was proportional to the extent of suppression in the folding defect, assuring that the in vivo defect associated with the Z variant is primarily derived from the folding block. In contrast, the folding and secretion efficiency of S(iiyama) was not much improved by the same mutations. In addition, none of the rarely secreted S(iiyama) alpha1-AT carrying the stabilizing mutations for the wild type and Z variant were active. It appears that the major defect in S(iiyama) variant is the loss of stability in contrast to the kinetic block of folding in the Z variant.

High-level secretion of human alpha 1-antitrypsin from Saccharomyces cerevisiae using inulinase signal sequence

The use of a proper signal sequence is one of the major determinants for the efficient secretion of heterologous proteins from yeast. The signal sequence derived from inulinase (INU1A) of Kluyveromyces marxianus was evaluated in directing the secretion of a human glycoprotein, alpha 1-antitrypsin (alpha 1-AT), from Saccharomyces cerevisiae. A yeast expression vector for alpha 1-AT was constructed by placing the coding sequence of human alpha 1-AT fused with the INU1A signal sequence downstream of the GAL10 promoter. S. cerevisiae transformants harboring the expression vector secreted about 70% of the total alpha 1-AT synthesized into the culture media. The intracellularly retained form of alpha 1-AT was mostly unglycosylated, whereas the secreted protein had high mannose-type glycosylation. The fed-batch cultivation of the recombinant yeast achieved a high-cell density, leading to the secretion of biologically active alpha 1-AT up to 75 mg l-1. The secreted protein was purified and subjected to N-terminal sequencing, which confirmed that the secreted alpha 1-AT was processed correctly at the Kex2 cleavage site as expected from the sequence of INU1A signal peptide. The results suggest that the inulinase signal sequence is useful for the high-level secretion of relatively large glycoproteins, such as human alpha 1-AT, from S. cerevisiae.

Effect of initiation factor eIF-5A depletion on protein synthesis and proliferation of Saccharomyces cerevisiae

Eukaryotic translation initiation factor eIF-5A (formerly eIF-4D) is thought to function in protein synthesis by promoting synthesis of the first peptide bond because it stimulates methionyl-puromycin formation in vitro. eIF-5A is encoded by two genes (TIF51A and TIF51B) in Saccharomyces cerevisiae; the protein and its hypusine modification are essential for cell viability. To analyze the factor's function in vivo, we expressed from the repressible GAL promoter a functional but unstable eIF-5A fusion protein (R-eIF-5A) with an NH2-terminal arginine which is subject to rapid turnover through the NH2-terminal end rule proteolytic pathway. When the conditional mutant strain is shifted from galactose to glucose medium, the rapid disappearance of R-eIF-5A protein occurs within one generation, causing an immediate inhibition of cell growth. However, eIF-5A-depleted cells synthesize protein at about 70% of the wild type rate and exhibit only a slight change in polysome profiles reflecting a subtle defect in a late step of translation initiation. These results suggest that the activity of eIF-5A may not be absolutely essential for general protein synthesis. Rather, eIF-5A may be selectively required for translation of certain mRNAs and/or may be involved in some other aspect of cell metabolism.

Effects of the par locus on the growth rate and structural stability of recombinant cells

A decreased growth rate of recombinant cells is observed when a cloned gene protein encoded in a multicopy plasmid is induced from a strong promoter. This negative effect on the cell growth rate may be the consequence of alternate use or reallocation of energy, precursor metabolites, and protein synthesizing machinery. In order to analyze the causes for this adverse effect, we have studied how genetic elements present in multicopy plasmids affect the growth of recombinant Escherichia coli (K12 delta H1 delta trpEA). Turning on of the PL promoter, whether or not protein-coding sequences were present downstream of the promoter, decreased the growth of the recombinant cells by 15-50%. This result suggests that the essential factor(s) for cell growth may be sequestered by the genetic elements present in the plasmids and thus may cause the decreased growth. The negative effect of the de-repressed PL promoters on cell growth was partially reversed when the par sequence from pSC101 was inserted into the same plasmid. In each case when the plasmid carried only the PL promoter, the PL promoter followed by the N-terminal part of the protein-coding region, or the PL promoter followed by complete sequences encoding a protein, the par sequence exhibited a positive effect on the growth rate of the recombinant cells, which usually grow at a slower rate than the host cell.(ABSTRACT TRUNCATED AT 250 WORDS)

Translation initiation factor eIF-5A, the hypusine-containing protein, is phosphorylated on serine in Saccharomyces cerevisiae

Translation initiation factor eIF-5A (formerly called eIF-4D) is a small, highly conserved protein in eukaryotic cells that undergoes a unique modification at one of its lysine residues to form hypusine. eIF-5A stimulates in vitro the synthesis of methionyl-puromycin, a model reaction for formation of the first peptide bond. In Saccharomyces cerevisiae eIF-5A is encoded by two highly homologous genes, TIF51A and TIF51B, and each gene gives rise to two hypusinated isoelectric variants, eIF-5Aa (more acidic) and eIF-5Ab (more basic). In order to study the structural and functional differences between the two isoforms, both isoelectric forms were purified from a yeast strain overexpressing TIF51A and were shown to stimulate identically the synthesis of methionyl-puromycin in a heterologous mammalian assay system. Pulse-chase labeling of yeast cells with [35S]methionine showed that the basic form, eIF-5Ab, is a precursor form of the acidic form, eIF-5Aa. Immunoprecipitation of 32P-labeled cell lysates with rabbit antibodies specific for yeast eIF-5A, phosphoprotein phosphatase treatment of eIF-5Aa, and phosphoamino acid analysis demonstrated that eIF-5Aa is generated by phosphorylation of eIF-5Ab on serine. Therefore eIF-5A undergoes two post-translational modifications, hypusination and phosphorylation, where the activity of the factor is dependent on the first but is not influenced in vitro by the second.

Translation initiation factor eIF-5A expressed from either of two yeast genes or from human cDNA. Functional identity under aerobic and anaerobic conditions

Translation initiation factor eIF-5A (previously named eIF-4D) is an essential and highly conserved protein in eukaryotic cells that promotes formation of the first peptide bond. One of its lysine residues is post-translationally modified by spermidine to form hypusine, a unique residue required for eIF-5A activity. In Saccharomyces cerevisiae eIF-5A is encoded by two highly homologous genes, TIF51A and TIF51B. The two genes are regulated reciprocally by oxygen, where under aerobic conditions TIF51A is expressed and TIF51B is repressed, and under anaerobic conditions the opposite occurs. In order to study the products of the two genes individually, yeast strains were constructed that express either TIF51A or TIF51B under control of a galactose promoter. Each gene gives rise to two isoelectric variants, eIF-5Aa (more acidic) and eIF-5Ab (more basic), both of which carry the hypusine modification. Expression of either TIF51A or TIF51B promotes growth under both aerobic and anaerobic conditions, indicating that the two gene products function indistinguishably. The human cDNA encoding eIF-5A also was expressed in yeast, and the plasmid shuffle technique was used to demonstrate that the human protein can substitute for the homologous yeast protein in vivo. These results indicate that human and yeast eIF-5A are not only conserved at the sequence level but are functionally interchangeable in vivo.

The two genes encoding protein synthesis initiation factor eIF-5A in Saccharomyces cerevisiae are members of a duplicated gene cluster

Translation initiation factor eIF-5A is an abundant protein in which a lysine residue is modified by spermidine to form the amino acid derivative, hypusine. The factor is encoded by two genes in Saccharomyces cerevisiae, called TIF51A and TIF51B, which are regulated reciprocally by oxygen and by heme. TIF51B, also called ANB1, is located on chromosome X in a region called COR. We physically mapped TIF51A and its associated serine tRNA2 gene by the method of chromosome fragmentation and pulsed-field gel electrophoresis. TIF51A maps 90 kb from the left end of chromosome V in a region called ARC. The COR and ARC regions contain CYC1 and CYC7, respectively, and appear to be duplications carrying numerous related genes. The arrangements of related genes in the two regions are incompatible with a duplication mechanism involving a circular intermediate.

Translation initiation factor 5A and its hypusine modification are essential for cell viability in the yeast Saccharomyces cerevisiae

Translation intitiation factor eIF-5A (previously named eIF-4D) is a highly conserved protein that promotes formation of the first peptide bond. One of its lysine residues is modified by spermidine to form hypusine, a posttranslational modification unique to eIF-5A. To elucidate the function of eIF-5A and determine the role of its hypusine modification, the cDNA encoding human eIF-5A was used as a probe to identify and clone the corresponding genes from the yeast Saccharomyces cerevisiae. Two genes named TIF51A and TIF51B were cloned and sequenced. The two yeast proteins are closely related, sharing 90% sequence identity, and each is ca. 63% identical to the human protein. The purified protein expressed from the TIF51A gene substitutes for HeLa eIF-5A in the mammalian methionyl-puromycin synthesis assay. Strains lacking the A form of eIF-5A, constructed by disruption of TIF51A with LEU2, grow slowly, whereas strains lacking the B form, in which HIS3 was used to disrupt TIF51B, show no growth rate phenotype. However, strains with both TIF51A and TIF51B disrupted are not viable, indicating that eIF-5a is essential for cell growth in yeast cells. Northern (RNA) blot analysis shows two mRNA species, a larger mRNA (0.9 kb) transcribed from TIF51A and a smaller mRNA (0.8 kb) encoded by TIF51B. Under the aerobic growth conditions of this study, the 0.8-kb TIF51B transcript is not detected in the wild-type strain and is expressed only when TIF51A is disrupted. The TIF51A gene was altered by site-directed mutagenesis at the site of hypusination by changing the Lys codon to that for Arg, thereby producing a stable protein that retains the positive charge but is not modified to the hypusine derivative. The plasmid shuffle technique was used to replace the wild-type gene with the mutant form, resulting in failure of the yeast cells to grow. This result indicates that hypusine very likely is required for the vital in vivo function of eIF-5A and suggests a precise, essential role for the polyamine spermidine in cell metabolism.