Secretion and processing of insulin precursors in yeast

Molecular engineering of insulin for recombinant expression in yeast

Since the first administration of insulin to a person with diabetes in 1922, scientific contributions from academia and industry have improved insulin therapy and access. The pharmaceutical need for insulin is now more than 40 tons annually, half of which is produced by recombinant secretory expression in Saccharomyces cerevisiae. We discuss how, in this yeast species, adaptation of insulin precursors by removable structural elements is pivotal for efficient secretory expression. The technologies reviewed have been implemented at industrial scale and are seminal for the supply of human insulin and insulin analogues to people with diabetes now and in the future. Engineering of a target protein with removable structural elements may provide a general approach to yield optimisation.

Lipofection mediated transfection fails for sea urchin coelomocytes

Molecular cloning, gene manipulation, gene expression, protein function, and gene regulation all depend on the introduction of nucleic acids into target cells. Multiple methods have been developed to facilitate such delivery including instrument based microinjection and electroporation, biological methods such as transduction, and chemical methods such as calcium phosphate precipitation, cationic polymers, and lipid based transfection, also known as lipofection. Here we report attempts to lipofect sea urchin coelomocytes using DOTAP lipofection reagent packaged with a range of molecules including fluorochromes, in addition to expression constructs, amplicons, and RNA encoding GFP. DOTAP has low cytotoxicity for coelomocytes, however, lipofection of a variety of molecules fails to produce any signature of success based on results from fluorescence microscopy and flow cytometry. While these results are negative, it is important to report failed attempts so that others conducting similar research do not repeat these approaches. Failure may be the outcome of elevated ionic strength of the coelomocyte culture medium, uptake and degradation of lipoplexes in the endosomal-lysosomal system, failure of the nucleic acids to escape the endosomal vesicles and enter the cytoplasm, and difficulties in lipofecting primary cultures of phagocytic cells. We encourage others to build on this report by using our information to optimize lipofection with a range of other approaches to work towards establishing a successful method of transfecting adult cells from marine invertebrates.

An Overview on Selection Marker Genes for Transformation of Saccharomyces cerevisiae

For genetic manipulation of yeast, numerous selection marker genes have been employed. These include prototrophic markers, markers conferring drug resistance, autoselection markers, and counterselectable markers. This chapter describes the different classes of selection markers and provides a number of examples for different applications.

Commemorating insulin's centennial: engineering insulin pharmacology towards physiology

The life-saving discovery of insulin in Toronto in 1921 is one of the most impactful achievements in medical history, at the time being hailed as a miracle treatment for diabetes. The insulin molecule itself, however, is poorly amenable as a pharmacological intervention, and the formidable challenge of optimizing insulin therapy has been ongoing for a century. We review early academic insights into insulin structure and its relation to self-association and receptor binding, as well as recombinant biotechnology, which have all been seminal for drug design. Recent developments have focused on combining genetic and chemical engineering with pharmaceutical optimization to generate ultra-rapid and ultra-long-acting, tissue-selective, or orally delivered insulin analogs. We further discuss these developments and propose that future scientific efforts in molecular engineering include realizing the dream of glucose-responsive insulin delivery.

A novel peptide design aids in the expression and its simplified process of manufacturing of Insulin Glargine in Pichia pastoris

Manufacturing of insulin and its analogues relied upon in vitro enzymatic cleavages of its precursor forms (single chain precursor, SCP) at both ends of a connecting peptide (C-peptide) that links the respective B-chain and A-chains to corresponding final forms. We have demonstrated a simplified approach of cleaving P. pastoris expressed SCP, distinctly at one site for conversion to insulin glargine. The design of the precursor was made in such a way that there is no C-peptide in the precursor which needs to be removed in the final product. Instead of traditional both side cleavage of the C-peptide and removing the C-peptide (by trypsin), followed by 2nd enzyme reaction (typically carboxipeptidase B), present work established only one side cleavage of the sequence by only trypsin converts the precursor to final insulin glargine product. The novel design of the precursor helped in producing insulin glargine in a single step with an application of single enzyme brought high degree of process efficiencies. Highly purified product was generated through two reversed phase high pressure chromatographic steps. Purified product was compared with the reference product Lantus®, for various physico-chemical and biological properties. Primary, secondary and tertiary structures as well as biological pharmaco-dynamic effects were found comparable. High cell density fermentation that gave a good yield of the SCP, a single step conversion to insulin glargine, enabled by a unique design of SCP and a distinct purification approach, has led to a simplified and economical manufacturing process of this important drug used to treat diabetes. KEY POINTS: • Novel concept for processing single chain precursor of insulin glargine • Simple and economic process for insulin glargine • Physicochemical characterization and animal Pharmacodynamics show similarity to Lantus.

Use YeastFab to Construct Genetic Parts and Multicomponent Pathways for Metabolic Engineering

Budding yeast, as a eukaryotic model organism, has well-defined genetic information and a highly efficient recombination system, making it a good host to produce exogenous chemicals. Since most metabolic pathways require multiple genes to function in coordination, it is usually laborious and time-consuming to construct a working pathway. To facilitate the construction and optimization of multicomponent exogenous pathways in yeast, we recently developed a method called YeastFab Assembly, which includes three steps: (1) make standard and reusable genetic parts, (2) construct transcription units from characterized parts, and (3) assemble a complete pathway. Here we describe a detailed protocol of this method.

First Reports of Effects of Insulin, Human-like Insulin Receptors and Adapter Proteins in Acanthamoeba castellanii

The insulin receptor (IR) and insulin-like growth factor 1 receptor (IGF1-R) play key roles in growth, regulation of nutrient metabolism and carbohydrate homeostasis. Insulin-like molecules in prokaryotes and other early life have been reported. However, an account of metabolic effects of insulin, transcriptomic evidence of expression of glucose transporting channels (GLUT) and homology modelling of IR and IGF1-R like proteins in unicellular life-forms have yet to be established. Acanthamoeba spp. has existed for about 2 billion years and is one of the earliest mitochondriate unicellular eukaryotic cells on Earth. Despite Acanthamoeba spp. being grown in a medium called peptone-yeast-glucose (PYG) for over 50 years, the mechanism and regulation of glucose uptake by IR or IGF1-R molecules in this microbe has not yet been reported. Several methods were utilized to validate the effects of insulin on trophozoites of A. castellanii, including: growth assays with insulin, estimation of glucose and potassium (K+) entry into the cell, and histology showing anabolic effects on proteins. Bioinformatic computational tools and homology modeling demonstrated the involvement of IR like proteins, GLUT, and adapter proteins in mediating the IR cascade. Growth assays showed proliferative effects in a dose range of 2.98-5.97 µmol/mL of insulin. After insulin exposure, A. castellanii trophozoites displayed enhanced Periodic acid-Sciff (PAS) staining. Amino acid sequence similarities and homology modelling revealed ACA1_163470 in Acanthamoeba spp. to be a homolog of human-IR. Acanthamoeba protein ACA1_336150 shares similarities with IGF1-R. Additionally, some proteins like ACA1_060920 have attributes of GLUT like channels on homology modelling and show similarity with human GLUT. Knowledge of IR and insulin effects in Acanthamoeba spp. contributes to its biology and advances current understanding behind the evolution of IR and IGF1-R signalling cascade.

Specific PCR method for detection of species origin in biochemical drugs via primers for the ATPase 8 gene by electrophoresis

A PCR method is described to identify the species origin of various animal and human tissue-derived biochemical drugs. Four commercialized drugs, including spermary tablets, compound embryonic bovine liver extract tablets, spleen aminopeptide solution, and placenta polypeptide injection, were used as a proof-of-principle in this study. Primers were designed to amplify conservative regions of mitochondrial cytochrome b and ATPase 8 genes from beef, pork, lamb and human DNA, respectively. The specificity of primers for ATPase 8 gene is found to be higher than those for cytochrome b under the given experimental conditions. The amplicon sizes of ATPase 8 were 212, 271, 293 and 405 bp for pork, beef, lamb and human tissue, respectively. The minimum detectable concentration of DNA sample for species identification is 0.05-0.5 pg·μL^-1. The species origin can be distinguished by this method in extremely low concentrations of template DNAs extracted. Conceivably, this PCR method for meat authentication may be extended to quality control of other biochemical drugs and raw materials. Graphical abstract A specific PCR method was developed for the detection of species origin in biochemical drugs via species-specific primers targeting mitochondrial ATPase 8 genes. The PCR products were separated by gel electrophoresis and species origins were indicated by comparison to references.

Pursuit of a perfect insulin

Insulin remains indispensable in the treatment of diabetes, but its use is hampered by its narrow therapeutic index. Although advances in peptide chemistry and recombinant DNA-based macromolecule synthesis have enabled the synthesis of structurally optimized insulin analogues, the growing epidemics of obesity and diabetes have emphasized the need for diabetes therapies that are more efficacious, safe and convenient. Accordingly, a broad set of drug candidates, targeting hyperglycaemia plus other disease abnormalities, is now progressing through the clinic. The development of an insulin therapy that is responsive to glucose concentration remains an ultimate goal, with initial prototypes now reaching the proof-of-concept stage. Simultaneously, the first alternatives to injectable delivery have progressed to registration.

Genetic basis of dyslipidemia in disease precipitation of coronary artery disease (CAD) associated type 2 diabetes mellitus (T2DM)

Type 2 diabetes mellitus (T2DM) and its complications are linked to environmental, clinical, and genetic factors. This review analyses the disorders of lipids and their genetics with respect to coronary artery disease (CAD) associated with T2DM. Cell organelles, hepatitis C-virus infection, reactive oxygen species produced in mitochondria, and defective insulin signaling due to the arrest of G1 phase to S phase transition of β-cells have significant roles in the precipitation of the diseases. Adiponectin is anti-inflammatory and anti-atherosclerotic and improves insulin resistance. Low-density lipoprotein (LDL) is atherosclerotic, and LDL-cholesterol in T2DM is associated with high-cardiovascular risk. Further, LDL cholesterol reduction significantly reduces cardiovascular morbidity and mortality. High-density lipoprotein (HDL) is also anti-atherosclerotic due to HDL associated paraoxonase-1 serum enzyme, which prevents LDL oxidative modifications and the development of CAD. Moreover, elevated apolipoprotein B and apolipoprotein A-I (ApoB/ApoA-I) ratio in plasma is also a risk factor for CAD. LDL receptor, adiponectin, and endocannabinoid receptor-1 genes are independently associated with CAD and T2DM. Polymorphism of Apo E2 (epsilon2) is a positive factor to increase the T2DM risk and Apo E4 (epsilon4) is a negative factor to reduce the disease risk. Taq 1B polymorphism of cholesterol ester transfer protein (CETP) gene contributes to the development of atherosclerosis, whereas haplotypes of APOA5, APOC3, APOC4, and APOC5 genes are in the same cluster and are independently associated with high plasma triglyceride level, CAD and T2DM. In conclusion, because various genes, LDLR, CETP, APOA5, Apo E, Apo B, and Apo A-I, are associated with the precipitation of CAD associated with T2DM, a personalized diet-gene intervention therapy may be advocated to reduce the disease precipitation.

Restriction site free cloning (RSFC) plasmid family for seamless, sequence independent cloning in Pichia pastoris

BACKGROUND

Tagging proteins is a standard method facilitating protein detection, purification or targeting. When tagging a certain protein of interest, it is challenging to predict which tag will give optimal results and will not interfere with protein folding, activity or yields. Ideally, multiple tags and positions are tested which however complicates molecular cloning and expression vector generation. In conventional cloning, tags are either added on PCR primers (requiring a distinct primer and PCR product per tag) or provided on the vector (typically leaving a restriction site scar).

RESULTS

Here we report a vector family of 40 plasmids allowing simple, seamless fusions of a single PCR product with various N- and C-terminal tags, signal sequences and promoters. The restriction site free cloning (RSFC) strategy presented in this paper relies on seamless cloning using type IIS restriction endonucleases. After cutting out a stuffer (placeholder) fragment from the vectors, a single PCR product can be directly inserted in frame into all 40 plasmids using blunt end or TA ligations, requiring only verification of the orientation. We have established a RSFC vector family for the commonly used protein expression host Pichia pastoris and demonstrated the system with the secretory expression of horseradish peroxidase (HRP). HRP fusions to four tags (Myc, FLAG, His, Strep) and two fusion proteins (GFP and MBP) showed a 31-fold difference in volumetric activities. C-terminal tagging caused in some cases almost a complete loss of function, whereas N-terminal tags showed moderate differences.

CONCLUSIONS

The RSFC vectors provide an unprecedented toolbox for expression optimization in P. pastoris. The results obtained with HRP underline the importance of comparing different tags to maximize activities of fusion proteins. In a similar fashion the RSFC strategy can be applied in other expression hosts to screen for optimal promoters, signal sequences or to facilitate the evaluation of (iso-) enzyme families.

Dual-Color Monitoring Overcomes the Limitations of Single Bioluminescent Reporters in Fast-Growing Microbes and Reveals Phase-Dependent Protein Productivity during the Metabolic Rhythms of Saccharomyces cerevisiae

Luciferase is a useful, noninvasive reporter of gene regulation that can be continuously monitored over long periods of time; however, its use is problematic in fast-growing microbes like bacteria and yeast because rapidly changing cell numbers and metabolic states also influence bioluminescence, thereby confounding the reporter's signal. Here we show that these problems can be overcome in the budding yeast Saccharomyces cerevisiae by simultaneously monitoring bioluminescence from two different colors of beetle luciferase, where one color (green) reports activity of a gene of interest, while a second color (red) is stably expressed and used to continuously normalize green bioluminescence for fluctuations in signal intensity that are unrelated to gene regulation. We use this dual-luciferase strategy in conjunction with a light-inducible promoter system to test whether different phases of yeast respiratory oscillations are more suitable for heterologous protein production than others. By using pulses of light to activate production of a green luciferase while normalizing signal variation to a red luciferase, we show that the early reductive phase of the yeast metabolic cycle produces more luciferase than other phases.

YeastFab: the design and construction of standard biological parts for metabolic engineering in Saccharomyces cerevisiae

It is a routine task in metabolic engineering to introduce multicomponent pathways into a heterologous host for production of metabolites. However, this process sometimes may take weeks to months due to the lack of standardized genetic tools. Here, we present a method for the design and construction of biological parts based on the native genes and regulatory elements in Saccharomyces cerevisiae. We have developed highly efficient protocols (termed YeastFab Assembly) to synthesize these genetic elements as standardized biological parts, which can be used to assemble transcriptional units in a single-tube reaction. In addition, standardized characterization assays are developed using reporter constructs to calibrate the function of promoters. Furthermore, the assembled transcription units can be either assayed individually or applied to construct multi-gene metabolic pathways, which targets a genomic locus or a receiving plasmid effectively, through a simple in vitro reaction. Finally, using β-carotene biosynthesis pathway as an example, we demonstrate that our method allows us not only to construct and test a metabolic pathway in several days, but also to optimize the production through combinatorial assembly of a pathway using hundreds of regulatory biological parts.

The genetics of a putative social trait in natural populations of yeast

The sharing of secreted invertase by yeast cells is a well-established laboratory model for cooperation, but the only evidence that such cooperation occurs in nature is that the SUC loci, which encode invertase, vary in number and functionality. Genotypes that do not produce invertase can act as ‘cheats’ in laboratory experiments, growing on the glucose that is released when invertase producers, or ‘cooperators’, digest sucrose. However, genetic variation for invertase production might instead be explained by adaptation of different populations to different local availabilities of sucrose, the substrate for invertase. Here we find that 110 wild yeast strains isolated from natural habitats, and all contained a single SUC locus and produced invertase; none were ‘cheats’. The only genetic variants we found were three strains isolated instead from sucrose-rich nectar, which produced higher levels of invertase from three additional SUC loci at their subtelomeres. We argue that the pattern of SUC gene variation is better explained by local adaptation than by social conflict.

Cell factories for insulin production

The rapid increase in the number of diabetic patients globally and exploration of alternate insulin delivery methods such as inhalation or oral route that rely on higher doses, is bound to escalate the demand for recombinant insulin in near future. Current manufacturing technologies would be unable to meet the growing demand of affordable insulin due to limitation in production capacity and high production cost. Manufacturing of therapeutic recombinant proteins require an appropriate host organism with efficient machinery for posttranslational modifications and protein refolding. Recombinant human insulin has been produced predominantly using E. coli and Saccharomyces cerevisiae for therapeutic use in human. We would focus in this review, on various approaches that can be exploited to increase the production of a biologically active insulin and its analogues in E. coli and yeast. Transgenic plants are also very attractive expression system, which can be exploited to produce insulin in large quantities for therapeutic use in human. Plant-based expression system hold tremendous potential for high-capacity production of insulin in very cost-effective manner. Very high level of expression of biologically active proinsulin in seeds or leaves with long-term stability, offers a low-cost technology for both injectable as well as oral delivery of proinsulin.

Production of recombinant human proinsulin in the milk of transgenic mice

There is a steady increasing demand for insulin worldwide. Current insulin manufacturing capacities can barely meet this increasing demand. The purpose of this study was to test the feasibility of producing human proinsulin in the milk of transgenic animals. Four lines of transgenic mice harboring a human insulin cDNA with expression driven by the goat β-casein gene promoter were generated. The expression level of human proinsulin in milk was as high as 8.1 g/L. The expression of the transgene was only detected in the mammary gland during lactation, with higher levels at mid-lactation and lower levels at early and late lactation. The blood glucose and insulin levels and the major milk compositions were unchanged, and the transgenic animals had no apparent health defects. The mature insulin derived from the milk proinsulin retained its biological activity. In conclusion, our study provides supporting evidence to explore the production of high levels of human proinsulin in the milk of dairy animals.

Multi-capillary column-ion mobility spectrometry of volatile metabolites emitted by Saccharomyces cerevisiae

Volatile organic compounds (VOCs) produced during microbial fermentations determine the flavor of fermented food and are of interest for the production of fragrances or food additives. However, the microbial synthesis of these compounds from simple carbon sources has not been well investigated so far. Here, we analyzed the headspace over glucose minimal salt medium cultures of Saccharomyces cerevisiae using multi-capillary column-ion mobility spectrometry (MCC-IMS). The high sensitivity and fast data acquisition of the MCC-IMS enabled online analysis of the fermentation off-gas and 19 specific signals were determined. To four of these volatile compounds, we could assign the metabolites ethanol, 2-pentanone, isobutyric acid, and 2,3-hexanedione by MCC-IMS measurements of pure standards and cross validation with thermal desorption-gas chromatography-mass spectrometry measurements. Despite the huge biochemical knowledge of the biochemistry of the model organism S. cerevisiae, only the biosynthetic pathways for ethanol and isobutyric acid are fully understood, demonstrating the considerable lack of research of volatile metabolites. As monitoring of VOCs produced during microbial fermentations can give valuable insight into the metabolic state of the organism, fast and non-invasive MCC-IMS analyses provide valuable data for process control.

Playing catch-up with Escherichia coli: using yeast to increase success rates in recombinant protein production experiments

Several host systems are available for the production of recombinant proteins, ranging from Escherichia coli to mammalian cell-lines. This article highlights the benefits of using yeast, especially for more challenging targets such as membrane proteins. On account of the wide range of molecular, genetic, and microbiological tools available, use of the well-studied model organism, Saccharomyces cerevisiae, provides many opportunities to optimize the functional yields of a target protein. Despite this wealth of resources, it is surprisingly under-used. In contrast, Pichia pastoris, a relative new-comer as a host organism, is already becoming a popular choice, particularly because of the ease with which high biomass (and hence recombinant protein) yields can be achieved. In the last few years, advances have been made in understanding how a yeast cell responds to the stress of producing a recombinant protein and how this information can be used to identify improved host strains in order to increase functional yields. Given these advantages, and their industrial importance in the production of biopharmaceuticals, I argue that S. cerevisiae and P. pastoris should be considered at an early stage in any serious strategy to produce proteins.

An overview on selection marker genes for transformation of Saccharomyces cerevisiae

For genetic manipulation of yeast, numerous selection marker genes have been employed. These include prototrophic markers, markers conferring drug resistance, autoselection markers, and counterselectable markers. This chapter describes the different classes of selection markers and provides a number of examples for different applications.

Short-term effects of INGAP and Reg family peptides on the appearance of small β-cells clusters in non-diabetic mice

The Reg3 peptides INGAP-PP and human Reg3α/β (HIP) have been hypothesized to stimulate β-cell neogenesis in the pancreas. Administration of INGAP-PP has been shown to cause an increase in β-cell mass in multiple animal models, reverse streptozotocin (STZ) induced diabetes in mice and reduces HbA1c levels in type 2 diabetic humans. In this study, we have examined the ability of the INGAP-PP and HIP peptides to induce β-cell formation in vivo in normal mice through short-term administration of the peptides. We assessed the peptides ability to induce an increase in extra-islet insulin-positive cell clusters by looking at β-cell number by point counting morphometry on pancreata that had been randomized using the smooth fractionator principle in non-diabetic NMRI mice after short-term injections of the peptides (5 d). Five day continuous BrdU labeling was used to determine if the new β-cells were derived from replicating β-cells. Real time quantitative RT-PCR and immuno-histochemistry was used to analyze changes in pancreatic transcription factor expression. A 1.5- to 2-fold increase in the volume of small extra-islet insulin-positive clusters post 5 d treatment with INGAP-PP and HIP as compared with mice treated with a non-peptide control or scrambled peptide (p<0.05) (n = 7) was found. Five day continuous BrdU infusion during the 5 d period showed little or no incorporation in islets or small insulin clusters. Five days of treatment with INGAP-PP or HIP, showed a tendency toward increased levels of pancreatic progenitor markers such as Ngn3, Nkx6.1, Sox9 and Ins. These are the first studies to compare and indicate that the human Reg3 α/β (HIP) peptide has similar bioactivity in vivo as INGAP by causing formation of small β-cell clusters in extra-islet pancreatic tissue after only 5 d of treatment. Upregulation of pancreatic transcription factors may be part of the mechanism of action.

Expression and characterization of human proinsulin fused to thioredoxin in Escherichia coli

Native proinsulin (PI) belongs to the class of the difficult-to-express proteins in Escherichia coli. Problems mainly arise due to its high proteolytic decay and troubles to reproduce the native disulphide pattern. In the present study, human PI was produced in E. coli as a fusion thioredoxin protein (Trx-PI). Such chimeric protein was obtained from the intracellular soluble fraction, and it was purified in one step by affinity chromatography on immobilized phenylarsine oxide. Trx-PI was also recovered from inclusion bodies and purified by anion exchange chromatography. The product identity and integrity were verified by mass analysis (22,173.5 Da) and mapping with Staphylococcus aureus V8 protease. Native PI folding was evaluated by biochemical and also by immunochemical analysis using specific sera from PI antibody-positive diabetic patients that recognise conformational discontinue epitopes. Dose-response curves showed identity between standard PI and Trx-PI. Moreover, surface plasmon resonance technique verified the correct conformation of the recombinant protein. The biochemical and immunochemical assays demonstrated the integrity of the chimera and the epitopes involved in the interaction with antibodies. In conclusion, it was possible to obtain with high-yield purified human PI as a fusion protein in E. coli and useful for analytical purposes.

Genome-scale metabolic models of Saccharomyces cerevisiae

Systematic analysis of Saccharomyces cerevisiae metabolic functions and pathways has been the subject of extensive studies and established in many aspects. With the reconstruction of the yeast genome-scale metabolic (GSM) network and in silico simulation of the GSM model, the nature of the underlying cellular processes can be tested and validated with the increasing metabolic knowledge. GSM models are also being exploited in fundamental research studies and industrial applications. In this chapter, the principle concepts for construction, simulation and validation of GSM models, progressive applications of the yeast GSM models, and future perspectives are described. This will support and encourage researchers who are interested in systemic analysis of yeast metabolism and systems biology.

Plant-made pharmaceuticals for the prevention and treatment of autoimmune diseases: where are we?

Molecular farming in plants or plant cell cultures represents a viable alternative technology that holds great promise for the low-cost and large-scale production of recombinant proteins. The particular case of plant-based vaccines for the prevention of autoimmune diseases is addressed here, presenting a comprehensive overview of the different molecules and expression technologies that have been investigated so far in both academia and industry. The potential of plants not only as bioreactors but also as delivery systems for pharmaceuticals is discussed, and the advantages of oral delivery of autoantigens for the induction of immune tolerance are highlighted.

Application of simple fed-batch technique to high-level secretory production of insulin precursor using Pichia pastoris with subsequent purification and conversion to human insulin

Background

The prevalence of diabetes is predicted to rise significantly in the coming decades. A recent analysis projects that by the year 2030 there will be ~366 million diabetics around the world, leading to an increased demand for inexpensive insulin to make this life-saving drug also affordable for resource poor countries.

Results

A synthetic insulin precursor (IP)-encoding gene, codon-optimized for expression in P. pastoris, was cloned in frame with the Saccharomyces cerevisiae α-factor secretory signal and integrated into the genome of P. pastoris strain X-33. The strain was grown to high-cell density in a batch procedure using a defined medium with low salt and high glycerol concentrations. Following batch growth, production of IP was carried out at methanol concentrations of 2 g L^-1, which were kept constant throughout the remaining production phase. This robust feeding strategy led to the secretion of ~3 gram IP per liter of culture broth (corresponding to almost 4 gram IP per liter of cell-free culture supernatant). Using immobilized metal ion affinity chromatography (IMAC) as a novel approach for IP purification, 95% of the secreted product was recovered with a purity of 96% from the clarified culture supernatant. Finally, the purified IP was trypsin digested, transpeptidated, deprotected and further purified leading to ~1.5 g of 99% pure recombinant human insulin per liter of culture broth.

Conclusions

A simple two-phase cultivation process composed of a glycerol batch and a constant methanol fed-batch phase recently developed for the intracellular production of the Hepatitis B surface antigen was adapted to secretory IP production. Compared to the highest previously reported value, this approach resulted in an ~2 fold enhancement of IP production using Pichia based expression systems, thus significantly increasing the efficiency of insulin manufacture.

Biomimetic synthesis of lispro insulin via a chemically synthesized "mini-proinsulin" prepared by oxime-forming ligation

Here we report a proof-of-principle study demonstrating the efficient folding, with concomitant formation of the correct disulfides, of an isolated polypeptide insulin precursor of defined covalent structure. We used oxime-forming chemical ligation to introduce a temporary "chemical tether" to link the N-terminal residue of the insulin A chain to the C-terminal residue of the insulin B chain; the tether enabled us to fold/form disulfides with high efficiency. Enzymatic removal of the temporary chemical tether gave mature, fully active insulin. This chemical tethering principle could form the basis of a practical, high yield total synthesis of insulin and analogues.

Recombinant expression of an insulin-like peptide 3 (INSL3) precursor and its enzymatic conversion to mature human INSL3

Insulin-like peptide 3 (INSL3), which is primarily expressed in the Leydig cells of the testes, is a member of the insulin superfamily of peptide hormones. One of its primary functions is to initiate and mediate descent of the testes of the male fetus via interaction with its G protein-coupled receptor, RXFP2. Study of the peptide has relied upon chemical synthesis of the separate A- and B-chains and subsequent chain recombination. To establish an alternative approach to the preparation of human INSL3, we designed and recombinantly expressed a single-chain INSL3 precursor in Escherichia coli cells. The precursor was solubilized from the inclusion body, purified almost to homogeneity by immobilized metal-ion affinity chromatography and refolded efficiently in vitro. The refolded precursor was subsequently converted to mature human INSL3 by sequential endoproteinase Lys-C and carboxypeptidase B treatment. CD spectroscopic analysis and peptide mapping showed that the refolded INSL3 possessed an insulin-like fold with the expected disulfide linkages. Recombinant human INSL3 demonstrated full activity in stimulating cAMP activity in RXFP2-expressing cells. Interestingly, the activity of the single-chain precursor was comparable with that of the mature two-chain INSL3, suggesting that the receptor-binding region within the mid- to C-terminal of B-chain is maintained in an active conformation in the precursor. This study not only provides an efficient approach for mature INSL3 preparation, but also resulted in the acquisition of a useful single-chain template for additional structural and functional studies of the peptide.

Periodic fermentor yield and enhanced product enrichment from autonomous oscillations

Four decades of work have clearly established the existence of autonomous oscillations in budding yeast culture across a range of operational parameters and in a few strains. Autonomous oscillations impact substrate conversion to biomass and products. Relatively little work has been done to quantify yield in this case. We have analyzed the yield of autonomously oscillating systems, grown under different conditions, and demonstrate that it too oscillates. Using experimental data and mathematical models of yeast growth and division, we demonstrate strategies to increase the efficient recovery of products. The analysis makes advantage of the population structure and synchrony of the system and our ability to target production within the cell cycle. While oscillatory phenomena in culture have generally been regarded with trepidation in the engineering art of bioprocess control, our results provide further evidence that autonomously oscillating systems can be a powerful tool, rather than an obstruction.

Insulin structure and function

Throughout much of the last century insulin served a central role in the advancement of peptide chemistry, pharmacology, cell signaling and structural biology. These discoveries have provided a steadily improved quantity and quality of life for those afflicted with diabetes. The collective work serves as a foundation for the development of insulin analogs and mimetics capable of providing more tailored therapy. Advancements in patient care have been paced by breakthroughs in core technologies, such as semisynthesis, high performance chromatography, rDNA-biosynthesis and formulation sciences. How the structural and conformational dynamics of this endocrine hormone elicit its biological response remains a vigorous area of study. Numerous insulin analogs have served to coordinate structural biology and biochemical signaling to provide a first level understanding of insulin action. The introduction of broad chemical diversity to the study of insulin has been limited by the inefficiency in total chemical synthesis, and the inherent limitations in rDNA-biosynthesis and semisynthetic approaches. The goals of continued investigation remain the delivery of insulin therapy where glycemic control is more precise and hypoglycemic liability is minimized. Additional objectives for medicinal chemists are the identification of superagonists and insulins more suitable for non-injectable delivery. The historical advancements in the synthesis of insulin analogs by multiple methods is reviewed with the specific structural elements of critical importance being highlighted. The functional refinement of this hormone as directed to improved patient care with insulin analogs of more precise pharmacology is reported.

Transgenic expression and recovery of biologically active recombinant human insulin from Arabidopsis thaliana seeds

The increased incidence of diabetes, coupled with the introduction of alternative delivery methods that rely on higher doses, is expected to result in a substantial escalation in the demand for affordable insulin in the future. Limitations in the capacity and economics of production will make it difficult for current manufacturing technologies to meet this demand. We have developed a novel expression and recovery technology for the economical manufacture of biopharmaceuticals from oilseeds. Using this technology, recombinant human precursor insulin was expressed in transgenic plants. Plant-derived insulin accumulates to significant levels in transgenic seed (0.13% total seed protein) and can be enzymatically treated in vitro to generate a product with a mass identical to that of the predicted product, DesB(30)-insulin. The biological activity of this product in vivo and in vitro was demonstrated using an insulin tolerance test in mice and phosphorylation assay performed in a mammalian cell culture system, respectively.