Expression and secretion of rice alpha-amylase by Saccharomyces cerevisiae

Germination of aged oat seeds associated with changes in antioxidant enzyme activity and storage compounds mobilization

Germination of aged seeds may be associated with specific metabolic changes. The objective of this study was to examine physiological and metabolic alterations before and after germination of control and aged oat (Avena sativa) seeds. The activity of antioxidant enzymes and the level of storage compounds were measured in the embryo and endosperm at 0, 4, 16, and 32 h of imbibition for control seeds and 0, 4, 16, 32, and 60 h of imbibition for medium vigor seeds after artificially accelerated aging; metabolomic changes were determined in embryos at 16 and 32 h of seed imbibition. In aged oat seeds, superoxide dismutase activity and catalase activity increased in the late imbibition stage. The content of soluble sugars decreased significantly in the later stages of imbibition, while the content of proteins increased in 32 h of seed imbibition eventually producing mannitol and proline. The mobilization of fat in deteriorated seeds was mainly through the sphingolipid metabolic pathway generated by cell growth-promoting dihydrosphingosine-1-phosphate. Ascorbic acid, avenanthramide and proline levels increased significantly at 60 h of imbibition, playing an important role in the germination of aged oat seeds.

Establishment of a signal peptide with cross-species compatibility for functional antibody expression in both Escherichia coli and Chinese hamster ovary cells

Signal peptides are short peptides located at the N-terminus of secreted proteins. They characteristically have three domains; a basic region at the N-terminus (n-region), a central hydrophobic core (h-region) and a carboxy-terminal cleavage region (c-region). Although hundreds of different signal peptides have been identified, it has not been completely understood how their features enable signal peptides to influence protein expression. Antibody-derived signal peptides are often used to prepare recombinant antibodies expressed by eukaryotic cells, especially Chinese hamster ovary (CHO) cells. However, when prokaryotic Escherichia coli (E. coli) are utilized in drug discovery processes, such as for phage display selection or antibody humanization, signal peptides have been selected separately due to the differences in the expression systems between the species. In this study, we successfully established a signal peptide that enables a functional antibody to be expressed in both prokaryotic and eukaryotic cells by focusing on the importance of having an Ala residue in the c-region of the signal sequence. We found that changing Ser to Ala at only two positions significantly augmented the anti-HER2 antigen binding fragment (Fab) expression in E. coli. In addition, this altered signal peptide also retained the ability to express functional anti-HER2 antibody in CHO cells. Taken together, the present findings indicate that the signal peptide can promote functional antibody expression in both prokaryotic E. coli and eukaryotic CHO cells. This finding will contribute to the understanding of signal peptides and accelerate therapeutic antibody research.

Effects of methanol feeding methods on chimeric α-amylase expression in continuous culture of Pichia pastoris

The effects of two types of methanol feeding methods in a continuous culture of Pichia system on the cell growth and recombinant protein expression were studied using chimeric alpha-amylase as a model protein. With the feeding of methanol by a DO-stat method, the alpha-amylase concentration in the fermentation broth increased with decreasing dilution rate and reached 173 mg/l at a dilution rate of 0.013 h(-1), at which the maximum volumetric productivity of alpha-amylase was obtained. Although almost the same productivity was attained at 0.04 h(-1) with continuous methanol feeding, the alpha-amylase concentration was one third that compared with feeding by the DO-stat method, that is, 55 mg/l. Furthermore, at this dilution rate, the medium volume needed per unit time was three times that required when DO-stat was used. Therefore, continuous culture with methanol feeding by the DO-stat method may be a promising method for the production of recombinant proteins on an industrial scale by Pichia pastoris.

SAMY, a novel mammalian reporter gene derived from Bacillus stearothermophilus alpha-amylase

The Bacillus stearothermophilus alpha-amylase (amyS) is a heat-stable monomeric exoenzyme which catalyses random hydrolysis of 1,4-alpha-glucosidic linkages in polyglucosans. The Bacillus alpha-amylase was engineered for use as an intracellular (AmyS(Delta S)) as well as a secreted reporter protein (SAMY; secreted alpha-amylase) in mammalian cells. The 5' end of amyS containing the prokaryotic secretion signal was either deleted (amyS(Delta S)) or replaced by a murine immunoglobulin secretion signal. SAMY was cloned under control of the cytomegalovirus promoter (P(CMV)) in a mammalian expression vector or the promoter of the human elongation factor 1 alpha (P(EF1 alpha)) in a lentiviral expression context. A variety of mammalian and human cell lines growing as monolayers, in suspension or as three-dimensional spheroids were transfected/transduced with SAMY- or amyS(Delta S)-encoding expression/lentiviral vectors and alpha-amylase activity was measured in cell lysates and culture supernatants. These experiments showed that SAMY and AmyS(Delta S) were either secreted or remained intracellular as highly sensitive reporter enzymes. SAMY expression and detection was fully compatible with established SEAP (human secreted alkaline phosphatase) and u-PA(LMW) (low molecular weight urokinase-type plasminogen activator) reporter systems and could be used to quantify expression of up to three independent genes in one culture supernatant.

Characterization of active barley alpha-amylase 1 expressed and secreted by Saccharomyces cerevisiae

Recombinant barley alpha-amylase 1 isozyme was constitutively secreted by Saccharomyces cerevisiae. The enzyme was purified to homogeneity by ultrafiltration and affinity chromatography. The protein had a correct N-terminal sequence of His-Gln-Val-Leu-Phe-Gln-Gly-Phe-Asn-Trp, indicating that the signal peptide was efficiently processed. The purified alpha-amylase had an enzyme activity of 1.9 mmol maltose/mg protein/min, equivalent to that observed for the native seed enzyme. The kcat/Km was 2.7 x 10(2) mM(-1) x s(-1), consistent with those of alpha-amylases from plants and other sources.

Effects of sugar concentration on recombinant human alpha(1)-antitrypsin production by genetically engineered rice cell

Productivity of recombinant human alpha(1)-antitrypsin (rAAT) with a genetically engineered rice cell using an inducible promoter has been studied by batch-wise and continuous production. A simple model explained the effect of proteases released from the disrupted cells on the rAAT degradation. Glucose concentration in the medium significantly affected the rAAT productivity in the continuous production, because the rAAT was induced by sugar depletion. When the fresh medium containing 5mM glucose was supplied to the continuous bioreactor, induction time was long and the productivity was low, indicating that the glucose concentration in the cells was high enough as to repress the promoter. When the glucose concentration in the fresh medium was reduced to 0.5mM, total amount of rAAT produced in 70h cultivation reached 6.7-7.6mg/g-dry cell, which was two times larger than the control medium without glucose.

High-level periplasmic expression in Escherichia coli using a eukaryotic signal peptide: importance of codon usage at the 5' end of the coding sequence

We investigated the ability of signal peptides of eukaryotic origin (human, mouse, and yeast) to efficiently direct model proteins to the Escherichia coli periplasm. These were compared against a well-characterized prokaryotic signal peptide-OmpA. Surprisingly, eukaryotic signal peptides can work very efficiently in E. coli, but require optimization of codon usage by codon-based mutagenesis of the signal peptide coding region. Analysis of the 5' of periplasmic and cytoplasmic E. coli genes shows some codon usage differences.

Microassay for rapid screening of alpha-amylase activity

A microassay was developed for measuring the activity of alpha-amylases in the nanogram enzyme concentration range, based on the use of dye-labeled cross-linked starch as the substrate, and the release of soluble colored fragments formed in enzyme hydrolysis. Reaction conditions were optimized to generate a linear correlation between the increase in absorbance and a reaction time of 0-10 min, as well as enzyme concentrations in the range of 0-50 ng. A standard curve for the conversion of absorbance to enzyme activity units was constructed. The protocol developed was applied to monitoring the production of ultralow concentrations of recombinant barley alpha-amylase in yeast cells.

Rapid, high-level expression of glycosylated rice alpha-amylase in transfected plants by an RNA viral vector

Tobamoviral vectors have been developed for the heterologous expression of glycoproteins in plants. The rice alpha-amylase gene (OS103) was placed under the transcriptional control of a tobamovirus subgenomic promoter in a RNA viral vector. One to two weeks after inoculation, transfected Nicotiana benthamiana plants accumulated glycosylated alpha-amylase to levels of at least 5% total soluble protein. The 46kDa recombinant enzyme was purified, and its structural and biological properties were analyzed. Post-translational modifications of the secreted protein were compared to rice alpha-amylase expressed in amylolytic strains of Pichia pastoris and Saccharomyces cerevisiae. Endo-H analysis revealed that the alpha-amylase was moderately glycosylated in transfected plants and hyperglycosylated in yeast.

Asparagine as a nitrogen source for improving the secretion of mouse alpha-amylase in Saccharomyces cerevisiae protease A-deficient strains

A modified chemically defined medium was achieved by using asparagine as a nitrogen source to increase the production of secreted mouse alpha-amylase in several Saccharomyces cerevisiae protease A-deficient (pep4) strains. The specific productivity (quantity) and the 53 kDa non-glycosylated active form (quality) of mouse salivary alpha-amylase in liquid medium containing asparagine was remarkably improved compared to media containing other nitrogen sources, including ammonium sulphate, glutamic acid, arginine, casamino acids, yeast extract and peptone. Similar improvement was also observed on starch solid agar regarding the clarity and size of the halo zone formed by alpha-amylase activity. Compared with ammonium sulphate, advantages of using asparagine as the nitrogen source in liquid or solid medium included increasing the cell mass of test strains, recovering the viability of protease-deficient strains to levels similar to the wild-type strain, and increasing the copy number of the mouse alpha-amylase expression vector in test strains. In turn, these advantages apparently contributed to the increase of secretion of mouse alpha-amylase in several test strains and especially in the protease A-deficient strains. In addition to demonstrating the use of modified chemically defined medium to improve the quality and quantity of secreted mouse alpha-amylase, this study also provides a new strategy to improve the secretion of heterologous proteins in protease A deficient strains.

Disruption of PMR1, encoding a Ca2+-ATPase homolog in Yarrowia lipolytica, affects secretion and processing of homologous and heterologous proteins

The Yarrowia lipolytica PMR1 gene (YlPMR1) is a Saccharomyces cerevisiae PMR1 homolog which encodes a putative secretory pathway Ca2+-ATPase. In this study, we investigated the effects of a YlPMR1 disruption on the processing and secretion of native and foreign proteins in Y. lipolytica and found variable responses by the YlPMR1-disrupted mutant depending on the protein. The secretion of 32-kDa mature alkaline extracellular protease (AEP) was dramatically decreased, and incompletely processed precursors were observed in the YlPMR1-disrupted mutant. A 36- and a 52-kDa premature AEP were secreted, and an intracellular 52-kDa premature AEP was also detected. The acid extracellular protease activity of the YlPMR1-disrupted mutant was increased by 60% compared to that of the wild-type strain. The inhibitory effect of mutations in secretory pathway Ca2+-ATPase genes on the secretion of rice alpha-amylase was also observed in the Y. lipolytica and S. cerevisiae PMR1-disrupted mutants. Unlike rice alpha-amylase, the secretion of Trichoderma reesei endoglucanase I (EGI) was not influenced by the YlPMR1 disruption. However, the secreted EGI from the YlPMR1-disrupted mutant had different characteristics than that of the control. While wild-type cells secreted the hyperglycosylated form of EGI, hyperglycosylation was completely absent in the YlPMR1-disrupted mutant. Our results indicate that the effects of the YlPMR1 disruption as manifested by the phenotypic response depend on the characteristics of the reporter protein in the recombinant yeast strain evaluated.

Utilization of antipeptide antibodies as affinity ligands in immunoaffinity purification

Anti-peptide antibodies against the C-terminal regions of chimeric alpha-amylase, recombinant CD2 and insulin B-chain were obtained by using peptides corresponding to the C-terminal regions as immunogens. These anti-peptide antibodies adsorbed the native proteins, as well as the antigen peptides. The proteins were purified to high purity using the anti-peptide antibodies as affinity ligands. These ligands could discriminate the target proteins having different C-terminal regions. The adsorbed proteins were specifically eluted by the eluents containing the antigen peptides.

Expression, secretion, and processing of rice alpha-amylase in the yeast Yarrowia lipolytica

The gene encoding rice alpha-amylase in Oryza sativa was expressed in the yeast Yarrowia lipolytica, which is a potential host system for heterologous protein expression. For efficient secretion, the strong and inducible XPR2 promoter was used in the construction of four kinds of expression vectors with the following configurations between the XPR2 promoter and terminator: 1) XPR2 prepro-region-rice alpha-amylase coding sequence, 2) rice alpha-amylase signal peptide-rice alpha-amylase coding sequence, 3) XPR2 signal peptide-rice alpha-amylase coding sequence, and 4) XPR2 signal peptide-dipeptide stretch-rice alpha-amylase coding sequence. Secretion of active recombinant rice alpha-amylase into the culture medium was achieved only in the first two cases, demonstrating that the XPR2 signal peptide is not sufficient to direct the secretion of heterologous protein. Furthermore, our study shows that the XPR2 prepro-region causes imprecise processing (after Pro150-Ala151 or Val135-Leu136 instead of Lys156-Arg157) and leads to N-terminal amino acid sequences that differ from that of native rice alpha-amylase. Secondary structure analysis proposed that the structural form in the vicinity of the KEX2-like endopeptidase processing site in the XPR2 pro-region might play a critical role in the processing of heterologous proteins. These results suggest that the XPR2 pro-region is dispensable for obtaining the precise N-terminal amino acid in heterologous protein secretion. In contrast, utilizing the rice alpha-amylase signal peptide was sufficient in directing secretion of recombinant protein with the expected N-terminal sequence, indicating that the signal peptide of rice alpha-amylase was effectively recognized and processed by the Y. lipolytica secretory pathway.

Characterization of rice alpha-amylase isozymes expressed by Saccharomyces cerevisiae

Two rice alpha-amylase isozymes, AmylA and Amy3D, were produced by secretion from genetically engineered strains of Saccharomyces cerevisiae. They have distinct differences in enzymatic characteristics that can be related to the physiology of the germinating rice seed. The rice isozymes were purified with immunoaffinity chromatography. The pH optima for Amy3D (pH optimum 5.5) and Amy1A (pH optimum 4.2) correlate with the pH of the endosperm tissue at the times in rice seedling development when these isozymes are produced. Amy3D showed 10-14 times higher reactivity to oligosaccharides than Amy1A. Amy1A, on the other hand, showed higher reactivity to soluble starch and starch granules than Amy3D. These results suggest that the isozyme Amy3D, which is expressed at an early stage of germination, produces sugars from soluble starch during the early stage of seed germination and that the isozyme Amy1A works to initiate hydrolysis of the starch granules.

Purification of recombinant alpha-amylase by immunoaffinity chromatography with anti-peptide antibody

Adsorption characteristics of an anti-peptide antibody, obtained by immunization of eight amino acids in the C-terminal region of chimeric alpha-amylase of rice alpha-amylase isozymes, were studied by use of the chimeric enzyme and the peptide used for immunization. This anti-peptide antibody adsorbed the enzyme, as well as the peptide antigen, with sufficient affinity for immunoaffinity purification and was used for purification of the enzyme secreted from yeast cells. Chimeric alpha-amylase was purified by immunoaffinity chromatography to high purity in one step from the fermentation broth. One-third of the secreted enzyme was not adsorbed by the column of anti-peptide antibody because of processing in the C-terminal region.

The roles of the N-linked carbohydrate chain of rice alpha-amylase in thermostability and enzyme kinetics

The thermostability and kinetics of starch hydrolysis were compared between a rice alpha-amylase isozyme Amy1A and its mutant enzyme that lacks an N-linked carbohydrate chain. Elimination of the N-glycosylation site in Amy1A reduced the thermostability of the enzyme. The temperature dependence of the kinetic parameters (Vm and Km) and substrate recognition of the enzymes were also affected by elimination of the N-glycosylation site. These results suggest that the N-linked carbohydrate chain of Amy1A has important roles in the thermostability and reaction kinetics of the enzyme.

Sequence-specific interactions of a nuclear protein factor with the promoter region of a rice gene for alpha-amylase, RAmy3D

The expression of a rice gene for alpha-amylase, RAmy3D, in suspension-cultured cells is induced at the transcriptional level by the deprivation of sugars. Binding of a nuclear protein from suspension-cultured rice cells to the promoter region of the RAmy3D gene was studied by gel-retardation and DNase I footprinting assays. Gel-retardation assays indicated that a 358-bp fragment of the promoter region interacted specifically with a protein factor from suspension-cultured cells. DNase I footprinting analysis allowed us to define three protein-binding regions. Each of these protein-binding sequences contained the GCCG G/C CG motif, which is specifically present in the promoter region of the sugar-regulated gene, RAmy3D, for rice alpha-amylase and not in that of the gibberellin-regulated RAmy1A gene. Subsequent cross-competition experiments using gel-retardation assay and synthetic oligonucleotides showed that the GCCG G/C CG motifs directly mediated the binding of a nuclear protein. These observations are discussed in relation to expression of the gene for alpha-amylase in suspension-cultured cells.

Conversion of starch to ethanol in a recombinant Saccharomyces cerevisiae strain expressing rice alpha-amylase from a novel Pichia pastoris alcohol oxidase promoter

A recombinant Saccharomyces cerevisiae, expressing and secreting rice alpha-amylase, converts starch to ethanol. The rice alpha-amylase gene (OS103) was placed under the transcriptional control of the promoter from a newly described Pichia pastoris alcohol oxidase genomic clone. The nucleotide sequences of ZZA1 and other methanol-regulated promoters were analyzed. A highly conserved sequence (TTG-N3-GCTTCCAA-N5-TGGT) was found in the 5' flanking regions of alcohol oxidase, methanol oxidase, and dihydroxyacetone synthase genes in Pichia pastoris, Hansenula polymorpha, and Candida boidinii S2. The yeast strain containing the ZZA1-OS103 fusion secreted biologically active enzyme into the culture media while fermenting soluble starch.

RAmy2A; a novel alpha-amylase-encoding gene in rice

The structure and expression of the alpha-amylase-encoding gene, RAmy2A, are described. This only representative of the Amy2 subfamily in rice differs from other cereal alpha-amylase-encoding genes in several respects. It contains the largest introns of all the cereal alpha-amylase-encoding genes examined to date. Moreover, the second of three introns in this gene contains a long inverted repeat sequence that can potentially form a large and stable stem-loop structure in the unspliced RNA transcript. Finally, RAmy2A is constitutively expressed at very low levels in germinated seeds, root, etiolated leaves, immature seeds and callus. This is in marked contrast to the Amy2 genes of wheat and barley which are highly expressed in the aleurone layer of the germinated seeds.

Gene expression in yeast: protein secretion

Maximizing efficiency for the secretion of proteins from yeast requires an understanding of the rate limiting stages in secretion that can result from high levels of gene expression. Recent progress in this area has produced a number of improvements in yeast expression systems for protein secretion.