Cloning and characterization of baker's yeast alpha-glucosidase: over-expression in a yeast strain devoid of vacuolar proteinases

The Development of Epitope-Based Recombinant Protein Vaccines against SARS-CoV-2

The COVID-19 pandemic continues to cause infections and deaths, which are attributable to the SARS-CoV-2 Omicron variant of concern (VOC). Moderna's response to the declining protective efficacies of current SARS-CoV-2 vaccines against Omicron was to develop a bivalent booster vaccine based on the Spike (S) protein from the Wuhan and Omicron BA.4/BA.5 strains. This approach, while commendable, is unfeasible in light of rapidly emerging mutated viral strains. PubMed and Google Scholar were systematically reviewed for peer-reviewed papers up to January 2024. Articles included focused on specific themes such as the clinical history of recombinant protein vaccine development against different diseases, including COVID-19, the production of recombinant protein vaccines using different host expression systems, aspects to consider in recombinant protein vaccine development, and overcoming problems associated with large-scale recombinant protein vaccine production. In silico approaches to identify conserved and immunogenic epitopes could provide broad protection against SARS-CoV-2 VOCs but require validation in animal models. The recombinant protein vaccine development platform has shown a successful history in clinical development. Recombinant protein vaccines incorporating conserved epitopes may utilize a number of expression systems, such as yeast (Saccharomyces cerevisiae), baculovirus-insect cells (Sf9 cells), and Escherichia coli (E. coli). Current multi-epitope subunit vaccines against SARS-CoV-2 utilizing synthetic peptides are unfeasible for large-scale immunizations. Recombinant protein vaccines based on conserved and immunogenic proteins produced using E. coli offer high production yields, convenient purification, and cost-effective production of large-scale vaccine quantities capable of protecting against the SARS-CoV-2 D614G strain and its VOCs.

Cloning and overexpression of a maltase gene from Schizosaccharomyces pombe in Escherichia coli and characterization of the recombinant maltase

The Schizosaccharomyces pombe maltase structural gene (SPMAL1(+)) was amplified from genomic DNA of S. pombe by PCR. An open reading frame of 1740bp, encoding a putative 579 amino-acid protein with a calculated molecular mass of 67.7kDa was characterized in the genomic DNA insert of plasmid pQE30. The specific maltase activity in the induced transformants was 21 times higher than that in wild-type. However, the estimated molecular mass of the purified recombinant maltase was 44.3kDa by sodium dodecyl sulphate polyacrylamide gel electrophoresis (SDS-PAGE). The optimal temperature and pH of the purified recombinant maltase were 40 degrees C and 6, respectively. The recombinant maltase was weakly activated by Mg(2+), Ca(2+), Na(+), and Ba(2+), but was strongly inhibited by Hg(2+), Ag(+) and Cu(2+), EDTA, and PMSF. The purified maltase could actively hydrolyse rho-nitrophenyl glucoside (PNPG), maltose, dextrin, and soluble starch. The results demonstrate that maltase from S. pombe was different from that from other yeasts, and might be usefully exploited in the future by the biotechnology industry or lead to the development of new molecular genetic tools.

An effective cold inducible expression system developed in Pseudoalteromonas haloplanktis TAC125

A regulative two-component system previously identified in Pseudoalteromonas haloplanktis TAC125 was used to construct a cold inducible expression system that is under the control of l-malate. Performances of the inducible system were tested for both psychrophilic and mesophilic protein production using two "difficult" proteins as control. The results obtained demonstrated that both psychrophilic beta-galactosidase and yeast alpha-glucosidase are produced in a fully soluble and catalytically competent form. Optimal conditions for protein production, including growth temperature, growth medium and l-malate concentration were also investigated. Under optimized conditions yields of 620 and 27 mg/l were obtained for beta-galactosidase and alpha-glucosidase, respectively.

Analysis of the interaction of small heat shock proteins with unfolding proteins

The ubiquitous small heat shock proteins (sHsps) are efficient molecular chaperones that interact with nonnative proteins, prevent their aggregation, and support subsequent refolding. No obvious substrate specificity has been detected so far. A striking feature of sHsps is that they form large complexes with nonnative proteins. Here, we used several well established model chaperone substrates, including citrate synthase, alpha-glucosidase, rhodanese, and insulin, and analyzed their interaction with murine Hsp25 and yeast Hsp26 upon thermal unfolding. The two sHsps differ in their modes of activation. In contrast to Hsp25, Hsp26 undergoes a temperature-dependent dissociation that is required for efficient substrate binding. Our analysis shows that Hsp25 and Hsp26 reacted in a similar manner with the nonnative proteins. For all substrates investigated, complexes of defined size and shape were formed. Interestingly, several different nonnative proteins could be incorporated into defined sHsp-substrate complexes. The first substrate protein bound seems to determine the complex morphology. Thus, despite the differences in quaternary structure and mode of activation, the formation of large uniform sHsp-substrate complexes seems to be a general feature of sHsps, and this unique chaperone mechanism is conserved from yeast to mammals.

Cloning of maltase gene from a methylotrophic yeast, Hansenula polymorpha

The Hansenula polymorpha maltase structural gene (HPMAL1) was isolated from a genomic library by hybridization of the library clones with maltase-specific gene probe. An open reading frame of 1695 nt encoding a 564 amino-acid protein with calculated molecular weight of 65.3 kD was characterized in the genomic DNA insert of the plasmid p51. The protein sequence deduced from the HPMAL1 exhibited 58 and 47% identity with maltases from Candida albicans and Saccharomyces carlsbergesis encoded by CAMAL2 and MAL62, respectively, and 44% identity with oligo-alpha-1,6-glucosidase from Bacillus cereus. The recombinant Hansenula polymorpha maltase produced in Escherichia coli hydrolyzed p-nitrophenyl-alpha-D-glucopyranoside (PNPG), sucrose, maltose and alpha-methylglucoside and did not act on melibiose, cellobiose, trehalose and o-nitrophenyl-beta-D-galactopyranoside (ONPG). The affinity of the recombinant enzyme for its substrates increased in the order maltose <alpha-methylglucoside <sucrose <PNPG. Southern analysis revealed presence of a single maltase gene in H. polymorpha. This is the first report on the maltase gene sequence from a methylotrophic yeast.

Influence of controlled glucose oscillations on a fed-batch process of recombinant Escherichia coli

The influence of glucose oscillations on cell growth and product formation of a recombinant Escherichia coli culture producing a heterologous alpha-glucosidase was studied in fed-batch cultures in a laboratory bioreactor. Glucose oscillations were created by an on/off-feeding mode in either fast cycles (1 min) or slow cycles (4 min) and compared to a process with constant glucose addition. The study indicates that glucose oscillations influence the product stability and the overgrowth of plasmid-free cells if such cultures are not performed under continuous pressure for selection of plasmid-containing cells. Although the glucose uptake capacity decreased after induction of the recombinant alpha-glucosidase in all cultures performed, the up-growth of plasmid-free cells during the production phase was strongly inhibited by fast oscillations. In contrast, plasmid-free cells grew up when constant feeding or slow cycles were applied. Our data suggest that the various feed protocols effect the specific carbon dioxide formation rate differently, with the highest production of carbon dioxide in the cultivations with fast cycles. In connection to product formation the initial alpha-glucosidase accumulation was the same in all cultures, but the stability of the product was significantly lower in the cultivation with slow cycles. Our results from laboratory experiments are discussed in relation to the mixing situation in large-scale bioreactors.

Aqueous two-phase systems as an alternative process route for the fractionation of small inclusion bodies

Aqueous two-phase protocols have been established which successfully generate highly purified preparations of small inclusion bodies (IBs) from whole cell homogenates. Particle size analysis of disruptates confirmed that intense disruption (concomitant with maximal product release) was compromised by the corelease of contaminating solutes and the micronisation of cell debris yielding a similar particle size range to the IBs (100-200 nm). PEG 300-phosphate systems enabled partial recovery of IBs in the top phase of ATPS. In contrast, PEG 8000-phosphate systems partitioned IBs more efficiently as a discrete sediment within the lower phase, whilst the majority of micronised debris remained in the interphase. The alpha-glucosidase IB yield and purity in ATPS was bettered only by analytical sucrose density gradient centrifugation, which is not readily scaleable for application in process operations. The successful recovery of such small IBs from complex homogenates highlights a generic role that ATPS techniques might play in the recovery and purification of new bioparticulate products (viral and plasmid gene therapy vectors, particulate protein vaccines etc.).

Stabilization of proteins and peptides in diagnostic immunological assays by the molecular chaperone Hsp25

Diagnostic assays for proteins devoid of enzymatic activity are becoming increasingly important. Antibodies generated against the respective proteins are used for their detection in enzyme-linked immunosorbent assay or patient sera are used to monitor disease-related antibodies against recombinantly produced antigens. A problem frequently encountered with these assays is that the proteins or fragments thereof used as standards have a limited shelf life. A similar problem arises when activities of labile enzymes are used for diagnostic detection. Here, we present a novel approach to 'stabilizing' enzymatic activity and antigenicity of proteins used for immunogenic detection by molecular chaperones. We have exploited the ability of molecular chaperones to keep proteins in their active conformation to overcome the biotechnological problems encountered in protein-based diagnostics of heart attack, stroke, and viral infections such as hepatitis C. We show that Hsp25, a member of the family of small heat shock proteins, known to act as a molecular chaperone in protein folding reactions, can stably bind labile standard proteins. Complex formation does not interfere with immunogenic detection and, importantly, antigenic as well as enzymatic activity remains constant for weeks. This strategy seems to be applicable to a wide range of assays involving unstable proteins, including the generation of vaccines.

cDNA cloning and characterisation of an alpha-glucosidase gene from potato (Solanum tuberosum L.)

Using an Arabidopsis thaliana expressed sequence tag with sequence similarity to human lysosomal alpha-glucosidase as a probe, a potato cDNA was isolated. The cDNA encodes a polypeptide with an Mr value of 105,400 and the most significant matches of the deduced amino acid sequence are with members of family 31 of glucosyl transferase. The potato cDNA was expressed in a strain of Saccharomyces cerevisiae that is deficient in maltase activity and unable to grow using maltose as a carbon source (ABYSMAL81). Expression of the potato cDNA in the mutant yeast strain restores its ability to use maltose as a carbon source for growth. Additionally, alpha-glucosidase activity could be measured in extracts of the yeast cells following complementation. A range of maltodextrins were substrates for this activity. The steady-state expression level of the potato alpha-glucosidase gene was low in most tissues examined, the highest levels occurring in sprouting tubers and source leaves.

Tandemly repeated 147 bp elements cause structural and functional variation in divergent MAL promoters of Saccharomyces cerevisiae

We have studied four novel MAL promoters isolated from a single strain of bakers' yeast. Within these promoters we have identified up to five tandem 147 bp repeats located between the MAL UAS region and the MALT TATA box. These repeats strongly reduce MALT (maltose permease) gene expression but only weakly reduce MALS (maltase) gene expression. Insertion of the 147 bp elements into the heterologous CYC1 promoter reduced expression when located between the CYC1 UAS and the TATA box, but not when located upstream of the UAS. We propose that these naturally occurring repeats have evolved as a mechanism to lower the level of MALT expression relative of MALS expression, thus avoiding possible toxic effects associated with over-expression from multiple copies of the permease gene.

A fusion protein designed for noncovalent immobilization: stability, enzymatic activity, and use in an enzyme reactor

We have designed a new method for enzyme immobilization using a fusion protein of yeast alpha-glucosidase containing at its C-terminus a polycationic hexa-arginine fusion peptide. This fusion protein can be directly adsorbed from crude cell extracts on polyanionic matrices in a specific, oriented fashion. Upon noncovalent immobilization by polyionic interactions, the stability of the fusion protein is not affected by pH-, urea-, or thermal-denaturation. Furthermore, the enzymatic properties (specific activity at increasing enzyme concentration, Michaelis constant, or activation energy of the enzymatic reaction) are not influenced by this noncovalent coupling. The operational stability of the coupled enzyme under conditions of continuous substrate conversion is, however, increased significantly compared to the soluble form. Fusion proteins containing polyionic peptide sequences are proposed as versatile tools for the production of immobilized enzyme catalysts.

Molecular cloning and characterization of a gibberellin-inducible, putative alpha-glucosidase gene from barley

A putative alpha-glucosidase clone has been isolated from a cDNA library constructed from mRNA of barley aleurones treated with gibberellin A 3 (GA). The clone is 2752 bp in length and has an uninterrupted open reading frame encoding a polypeptide of 877 amino acids. A 680 amino acid region is 43% identical to human lysosomal alpha-glucosidase and other glycosyl hydrolases. In isolated aleurones, the levels of the corresponding mRNA increase strongly after the application of GA, similar to the pattern exhibited by low-pI alpha-amylase mRNA. High levels are also observed in the aleurone and scutellum after germination, while low levels are found in developing seeds. The genome contains a single form of this alpha-glucosidase gene and two additional sequences that may be related genes or pseudogenes.

Glycoprotein biosynthesis in Saccharomyces cerevisiae: ngd29, an N-glycosylation mutant allelic to och1 having a defect in the initiation of outer chain formation

Outer chain glycosylation in Saccharomyces cerevisiae leads to heterogeneous and immunogenic asparagine-linked saccharide chains containing more than 50 mannose residues on secreted glycoproteins. Using a [3H]mannose suicide selection procedure a collection of N-glycosylation defective mutants (designated ngd) was isolated. One mutant, ngd29, was found to have a defect in the initiation of the outer chain and displayed a temperature growth sensitivity at 37 degrees C allowing the isolation of the corresponding gene by complementation. Cloning, sequencing and disruption of NGD29 showed that it is a non lethal gene and identical to OCH1. It complemented both the glycosylation and growth defect. Membranes isolated from an ngd29 disruptant or an ngd29mnn1 double mutant were no longer able, in contrast to membranes from wild type cells, to transfer mannose from GDPmannose to Man8GlcNAc2, the in vivo acceptor for building up the outer chain. Heterologous expression of glucose oxidase from Aspergillus niger in an ngd29mnn1 double mutant produced a secreted uniform glycoprotein with exclusively Man8GlcNAc2 structure that in wild type yeast is heavily hyperglycosylated. The data indicate that this mutant strain is a suitable host for the expression of recombinant glycoproteins from different origin in S. cerevisiae to obtain mammalian oligomannosidic type N-linked carbohydrate chains.

Characterization of a genetic locus essential for maltose-maltotriose utilization in Staphylococcus xylosus

A genetic locus from Staphylococcus xylosus involved in maltose-maltotriose utilization has been characterized. The chromosomal region was identified by screening a genomic library of S. xylosus in Escherichia coli for sucrose hydrolase activity. Nucleotide sequence analysis yielded two open reading frames (malR and malA) encoding proteins of 37.7 and 62.5 kDa, respectively. MalR was found to be homologous to the LacI-GalR family of transcriptional regulators, and MalA showed high similarity to yeast alpha-1,4-glucosidases and bacterial alpha-1,6-glucosidases. Inactivation of malA in the genome of S. xylosus led to a maltose-maltotriose-negative phenotype. In cell extracts of the mutant, virtually no glucose release from maltose and short maltodextrins was detectable. Inactivation of malA in a sucrose-6-phosphate hydrolase-deficient S. xylosus strain resulted in the complete loss of the residual sucrose hydrolase activity. The MalA enzyme has a clear preference for maltose but is also able to release glucose from short maltosaccharides. It cannot cleave isomaltose. Therefore, malA encodes an alpha-1,4-glucosidase or maltase, which also liberates glucose from sucrose. Subcloning experiments indicated that malA does not possess its own promoter and is cotranscribed with malR. Its expression could not be stimulated when maltose was added to the growth medium. Chromosomal inactivation of malR led to reduced maltose utilization, although alpha-glucosidase activity in the malR mutant was slightly higher than in the wild type. In the mutant strain, maltose uptake was reduced and inducibility of the transport activity was partially lost. It seems that MalR participates in the regulation of the gene(s) for maltose transport and is needed for their full expression. Thus, the malRA genes constitute an essential genetic locus for maltosaccharide utilization in S. xylosus

The archaebacterial membrane protein bacterio-opsin is expressed and N-terminally processed in the yeast Saccharomyces cerevisiae

The bop gene codes for the membrane protein bacterio-opsin (BO), which on binding all-trans-retinal, constitutes the light-driven proton pump bacteriorhodopsin (BR) in the archaebacterium Halobacterium salinarium. This gene was cloned in a yeast multi-copy vector and expressed in Saccharomyces cerevisiae under the control of the constitutive ADH1 promoter. Both the authentic gene and a modified form lacking the precursor sequence were expressed in yeast. Both proteins are incorporated into the membrane in S. cerevisiae. The presequence is thus not required for membrane targeting and insertion of the archaebacterial protein in budding yeast, or in the fission yeast Schizosaccharomyces pombe, as has been shown previously. However, in contrast to S. pombe transformants, which take on a reddish colour when all-trans-retinal is added to the culture medium as a result of the in vivo regeneration of the pigment, S. cerevisiae cells expressing BO do not take on a red colour. The precursor of BO is processed to a protein identical in size to the mature BO found in the purple membrane of Halobacterium. The efficiency of processing in S. cerevisiae is dependent on growth phase, as well as on the composition of the medium and on the strain used. The efficiency of processing of BR is reduced in S. pombe and in a retinal-deficient strain of H. salinarium, when retinal is present in the medium.

A zinc finger protein from Candida albicans is involved in sucrose utilization

A sucrose-inducible alpha-glucosidase activity that hydrolyzes sucrose in Candida albicans has been demonstrated previously. The enzyme is assayable in whole cells and was inhibited by both sucrose and maltose. A C. albicans gene (CASUC1) that affects sucrose utilization and alpha-glucosidase activity was cloned by expression in a Saccharomyces cerevisiae suc2 mutant (2102) devoid of invertase genes. CASUC1 enabled the S. cerevisiae mutant to utilize both sucrose and maltose. DNA sequence analysis revealed that CASUC1 encodes a putative zinc finger-containing protein with 28% identity to a maltose-regulatory gene (MAL63) of S. cerevisiae. The gene products of CASUC1 and MAL63 are approximately the same size (501 and 470 amino acids, respectively), and each contains a single zinc finger located at the N terminus. The zinc fingers of CASUC1 and MAL63 comprise six conserved cysteines (C6 zinc finger) and are of the general form Cys-Xaa2-Cys-Xaa6-Cys-Xaavariable-Cys-Xaa2-Cys-+ ++Xaa6-Cys (where Xaan indicates a stretch of the indicated number of any amino acids). Both contain five amino acids in the variable region. CASUC1 also complemented the maltose utilization defect of an S. cerevisiae mutant (TCY-137) containing a defined mutation in a maltose-regulatory gene. The sucrose utilization defect of type II Candida stellatoidea, a sucrase-negative mutant of C. albicans, was corrected by CASUC1. Determinations of alpha-glucosidase activity in whole cells revealed that activity was restored in transformants cultivated on either sucrose or maltose. To our knowledge, this is the first zinc finger-encoding gene, as well as the first putative regulatory gene, to be identified in C. albicans.

Primary structure and processing of the Candida tsukubaensis alpha-glucosidase. Homology with the rabbit intestinal sucrase-isomaltase complex and human lysosomal alpha-glucosidase

The nucleotide sequence of a 4.39-kb DNA fragment encoding the alpha-glucosidase gene of Candida tsukubaensis is reported. The cloned gene contains a major open reading frame (ORF 1) which encodes the alpha-glucosidase as a single precursor polypeptide of 1070 amino acids with a predicted molecular mass of 119 kDa. N-terminal amino acid sequence analysis of the individual subunits of the purified enzyme, expressed in the recombinant host Saccharomyces cerevisiae, confirmed that the alpha-glucosidase precursor is proteolytically processed by removal of an N-terminal signal peptide to yield the two peptide subunits 1 and 2, of molecular masses 63-65 kDa and 50-52 kDa, respectively. Both subunits are secreted by the heterologous host S. cerevisiae in a glycosylated form. Coincident with its efficient expression in the heterologous host, the C. tsukubaensis alpha-glucosidase gene contains many of the canonical features of highly expressed S. cerevisiae genes. There is considerable sequence similarity between C. tsukubaensis alpha-glucosidase, the rabbit sucrase-isomaltase complex (proSI) and human lysosomal acid alpha-glucosidase. The cloned DNA fragment from C. tsukubaensis contains a second open reading frame (ORF 2) which has the capacity to encode a polypeptide of 170 amino acids. The function and identity of the polypeptide encoded by ORF 2 is not known.

Identification of the upstream activating sequence of MAL and the binding sites for the MAL63 activator of Saccharomyces cerevisiae

Maltose fermentation in Saccharomyces species requires the presence of at least one of five unlinked MAL loci: MAL1, MAL2, MAL3, MAL4, and MAL6. Each of these loci consists of a complex of genes involved in maltose metabolism; the complex includes maltase, a maltose permease, and an activator of these genes. At the MAL6 locus, the activator is encoded by the MAL63 gene. While the MAL6 locus has been the subject of numerous studies, the binding sites of the MAL63 activator have not been determined. In this study, we used Escherichia coli extracts containing the MAL63 protein to define the binding sites of the MAL63 protein in the divergently transcribed MAL61-62 promotor. When a DNA fragment containing these sites was placed upstream of a CYC1-lacZ gene, maltose induced beta-galactosidase. These sites therefore constitute an upstream activating sequence for the MAL genes.

Identification of the upstream activating sequence of MAL and the binding sites for the MAL63 activator of Saccharomyces cerevisiae

Maltose fermentation in Saccharomyces species requires the presence of at least one of five unlinked MAL loci: MAL1, MAL2, MAL3, MAL4, and MAL6. Each of these loci consists of a complex of genes involved in maltose metabolism; the complex includes maltase, a maltose permease, and an activator of these genes. At the MAL6 locus, the activator is encoded by the MAL63 gene. While the MAL6 locus has been the subject of numerous studies, the binding sites of the MAL63 activator have not been determined. In this study, we used Escherichia coli extracts containing the MAL63 protein to define the binding sites of the MAL63 protein in the divergently transcribed MAL61-62 promotor. When a DNA fragment containing these sites was placed upstream of a CYC1-lacZ gene, maltose induced beta-galactosidase. These sites therefore constitute an upstream activating sequence for the MAL genes.

Two staining methods for selectively detecting isomaltase and maltase activity in electrophoresis gels

Two methods for specifically detecting maltase, alpha-glucosidase, or isomaltase activity in electrophoresis gels are described. Both systems couple the formation of glucose by enzyme action on maltose or isomaltose to the generation of a colored product. System A uses an agarose overlay which contains substrate, glucose oxidase, peroxidase, 2,4-dichlorophenol, and 4-L-amino-phenazone. A purple color is produced at the site of enzyme activity. No hazardous chemicals are used at any stage. The stain is simple, rapid, sensitive, and inexpensive and does not interfere with subsequent protein staining. However, the stain is not permanent. System B was developed to give a permanent stain. The gel is overlaid with agarose containing substrate, glucose oxidase, phenazine methosulfate, and nitroblue tetrazolium. Glucose production results in the nitroblue tetrazolium being oxidized to an insoluble formazan with a dark blue color. This stain is also sensitive, rapid, and inexpensive but does use hazardous chemicals and if overstaining occurs this can interfere with subsequent protein staining. Neither system inactivates the localized enzymes which can be recovered from the gel if desired.

Control of formation of active soluble or inactive insoluble baker's yeast alpha-glucosidase PI in Escherichia coli by induction and growth conditions

Using standard growth conditions (LB medium, 37 degrees C, induction with 5 mM IPTG) yeast alpha-glucosidase PI expressed under the control of the regulated tac-hybrid promoter results in the synthesis of insoluble aggregated alpha-glucosidase granules in Escherichia coli. Under these conditions active soluble alpha-glucosidase amounts to less than 1% of the heterologously produced protein. However, the amount of soluble active alpha-glucosidase was dramatically increased when the strong tac-hybrid promoter was to a limited extent induced. This was achieved at concentrations of 0.01 mM IPTG or of 1% lactose or lower in a lactose-permease deficient host strain containing the lacIq repressor gene on an R-plasmid. The formation of active soluble alpha-glucosidase was almost 100% when E. coli cells induced in this manner were cultivated under conditions that reduced growth rate, i.e. at decreased temperature, extreme pH values or in minimal and complete media supplemented with different carbon sources.