Production of protein-based polymers in Pichia pastoris

An engineered Pichia pastoris platform for the biosynthesis of silk-based nanomaterials with therapeutic potential

Silk fibroin (SF) from the cocoon of silkworm has exceptional mechanical properties and biocompatibility and is used as a biomaterial in a variety of fields. Sustainable, affordable, and scalable manufacturing of SF would enable its large-scale use. We report for the first time the high-level secretory production of recombinant SF peptides in engineered Pichia pastoris cell factories and the processing thereof to nanomaterials. Two SF peptides (BmSPR3 and BmSPR4) were synthesized and secreted by P. pastoris using signal peptides and appropriate spacing between hydrophilic sequences. By strain engineering to reduce protein degradation, increase glycyl-tRNA supply, and improve protein secretion, we created the optimized P. pastoris chassis PPGSP-8 to produce BmSPR3 and BmSPR4. The SF fed-batch fermentation titers of the resulting two P. pastoris cell factories were 11.39 and 9.48 g/L, respectively. Protein self-assembly was inhibited by adding Tween 80 to the medium. Recombinant SF peptides were processed to nanoparticles (NPs) and nanofibrils. The physicochemical properties of nanoparticles R3NPs and R4NPs from the recombinant SFs synthesized in P. pastoris cell factories were similar or superior to those of RSFNPs (Regenerated Silk Fibroin NanoParticles) originating from commercially available SF. Our work will facilitate the production by microbial fermentation of functional SF for use as a biomaterial.

Potential use of yeast protein in terms of biorefinery, functionality, and sustainability in food industry

A growing demand for sustainable, alternative protein sources that are nutrient-dense, such as microorganisms, and insects, has gradually evolved. When paired with effective processing techniques, yeast cells contain substantial substances that could supply the population's needs for food, medicine, and fuel. This review article explores the potential of yeast proteins as a sustainable and viable alternative to animal and plant-based protein sources. It highlights the various yeast protein extraction methods including both mechanical and non-mechanical methods. The application of nanoparticles is one example of the fast-evolving technology used to damage microbial cells. SiO2 or Al2O3 nanoparticles break yeast cell walls and disrupt membranes, releasing intracellular bioactive compounds. Succinylation of yeast protein during extraction can increase yeast protein extraction rate, lower RNA concentration, raise yeast protein solubility, increase amino acid content, and improve yeast protein emulsification and foaming capabilities. Combining physical and enzymatic extraction methods generates the most representative pool of mannose proteins from yeast cell walls. Ethanol or isoelectric precipitation purifies mannose proteins. Mannoproteins can be used as foamy replacement for animal-derived components like egg whites due to their emulsification, stability, and foaming capabilities. Yeast bioactive peptide was separated by ultrafiltration after enzymatic hydrolysis of yeast protein and has shown hypoglycemic, hypotensive, and oxidative action in vitro studies. Additionally, the review delves into the physicochemical properties and stability of yeast-derived peptides as well as their applications in the food industry. The article infers that yeast proteins are among the promising sources of sustainable protein, with a wide range of potential applications in the food industry.

Therapeutic proteins: developments, progress, challenges, and future perspectives

Proteins are considered magic molecules due to their enormous applications in the health sector. Over the past few decades, therapeutic proteins have emerged as a promising treatment option for various diseases, particularly cancer, cardiovascular disease, diabetes, and others. The formulation of protein-based therapies is a major area of research, however, a few factors still hinder the large-scale production of these therapeutic products, such as stability, heterogenicity, immunogenicity, high cost of production, etc. This review provides comprehensive information on various sources and production of therapeutic proteins. The review also summarizes the challenges currently faced by scientists while developing protein-based therapeutics, along with possible solutions. It can be concluded that these proteins can be used in combination with small molecular drugs to give synergistic benefits in the future.

Sustainable utilization of fruit and vegetable waste bioresources for bioplastics production

Nowadays, rapidly increasing production, use and disposable of plastic products has become one of the utmost environmental issues. Our current circumstances in which the food supply chain is demonstrated as containing plastic particles and other plastic-based impurities, represents a significant health risk to humans, animals, and environmental alike. According to this point of view, biodegradable plastic material aims to produce a more sustainable and greener world with a lower ecological impact. Bioplastics are being investigated as an environmentally friendly candidate to address this problem and hence global bioplastic production has seen significant growth and expansion in recent years. This article focuses on a few critical issues that must be addressed for bioplastic production to become commercially viable. Although the reduction of fruit and vegetable waste biomass has an apparent value in terms of environmental benefits and sustainability, commercial success at industrial scale has remained flat. This is due to various factors, including biomass feedstocks, pretreatment technologies, enzymatic hydrolysis, and scale-up issues in the industry, all of which contribute to high capital and operating costs. This review paper summarizes the global overview of bioplastics derived from fruit and vegetable waste biomass. Furthermore, economic and technical challenges associated with industrialization and diverse applications of bioplastics in biomedical, agricultural, and food-packaging fields due to their excellent biocompatibility properties are reviewed.HighlightsReview of the diverse types and characteristics of sustainability of biobased plasticsImproved pretreatment technologies can develop to enhance greater yieldEnzyme hydrolysis process used for bioplastic extraction & hasten industrial scale-upFocus on technical challenges facing commercialized the bioplasticsDetailed discussion on the application for sustainability of biodegradable plastics.

Dietary proteins: from evolution to engineering

Because of the indispensable amino acids dietary proteins are the most important macronutrients. Proper growth and body maintenance depends on the quantity and quality of protein intake and proteins have thus been most crucial throughout evolution with hominins living in quite diverse food ecosystems. Developments in agriculture and food science have increased availability and diversity of food including protein for a rapidly growing world population while nutrient deficiencies resulting in stunting in children for example have been reduced. Nevertheless, the developing world and growing population needs more protein of high quality - with around 400 million tons per annum estimated for 2050. In contrary, protein consumption in all developed countries exceeds meanwhile the recommended intakes considerably with consequences for health and the environment. There is a growing interest in dietary proteins driven by the quest for more sustainable diets and the increasing food demand for a growing world population. This brings new and novel sources such as algae, yeast, insects or bacteria into play in delivering the biomass but also new technologies such as precision fermentation or in vitro meat/fish or dairy. What needs to be considered when such new protein sources are explored is that proteins need to provide not only the required amino acids but also functionality in the food produced thereof. This review considers human physiology and metabolism in the context of protein intake from an evolutionary perspective and prospects on future protein production.

Functionalizing natural polymers to develop green adsorbents for wastewater treatment applications

The present study provides an overview of scientific developments made in the last decade in the field of green adsorbents focusing on the modifications in natural polymers and their applications such as, wastewater treatment, and ion exchange. For this purpose, an introduction to the various methods of modifying natural polymers is first given, and then the properties, application, and future priorities of green adsorbents are also discussed. Methods of modification of natural polymers under homogeneous and heterogeneous conditions using modifiers with different properties are also described. Various methods for modifying natural polymers and the use of the obtained green adsorbents are reviewed. A comparison of the sorption properties of green adsorbents based on natural polymers and other adsorbents used in industry has also been carried out. With the participation of green adsorbents based on natural polymers, the properties of treated wastewaters having toxic metal ions, organic dyes, petroleum products, and other harmful compounds was analyzed. Future perspectives on green adsorbents based on natural polymers are as also highlighted.

Customizing amino acid metabolism of Pichia pastoris for recombinant protein production

Amino acids are the building blocks of proteins. In this respect, a reciprocal effect of recombinant protein production on amino acid biosynthesis as well as the impact of the availability of free amino acids on protein production can be anticipated. In this study, the impact of engineering the amino acid metabolism on the production of recombinant proteins was investigated in the yeast Pichia pastoris (syn Komagataella phaffii). Based on comprehensive systems-level analyses of the metabolomes and transcriptomes of different P. pastoris strains secreting antibody fragments, cell engineering targets were selected. Our working hypothesis that increasing intracellular amino acid levels could help unburden cellular metabolism and improve recombinant protein production was examined by constitutive overexpression of genes related to amino acid metabolism. In addition to 12 genes involved in specific amino acid biosynthetic pathways, the transcription factor GCN4 responsible for regulation of amino acid biosynthetic genes was overexpressed. The production of the used model protein, a secreted carboxylesterase (CES) from Sphingopyxis macrogoltabida, was increased by overexpression of pathway genes for alanine and for aromatic amino acids, and most pronounced, when overexpressing the regulator GCN4. The analysis of intracellular amino acid levels of selected clones indicated a direct linkage of improved recombinant protein production to the increased availability of intracellular amino acids. Finally, fed batch cultures showed that overexpression of GCN4 increased CES titers 2.6-fold, while the positive effect of other amino acid synthesis genes could not be transferred from screening to bioreactor cultures.

Towards unlocking the biocontrol potential of Pichia kudriavzevii for plant fungal diseases: in vitro and in vivo assessments with candidate secreted protein prediction

BACKGROUND

Plant fungal pathogens cause substantial economic losses through crop yield reduction and post-harvest storage losses. The utilization of biocontrol agents presents a sustainable strategy to manage plant diseases, reducing the reliance on hazardous chemical. Recently, Pichia kudriavzevii has emerged as a promising biocontrol agent because of its capacity to inhibit fungal growth, offering a potential solution for plant disease management.

RESULTS

Two novel Pichia kudriavzevii strains, Pk_EgyACGEB_O1 and Pk_EgyACGEB_O2, were isolated from olive brine samples. The microscopic characterization of the strains revealed similar structures. However, there were noticeable differences in their visual morphology. Based on their internal transcribed spacer (ITS) DNA sequences, Pk_EgyACGEB_O1 and Pk_EgyACGEB_O2 strains assigned by GenBank IDs MZ507552.1 and MZ507554.1 shared high sequence similarity (~ 99.8% and 99.5%) with P. kudriavzevii, respectively. Both strains were evaluated in vitro against plant pathogenic fungi. The strains revealed the ability to consistently inhibit fungal growth, with Pk_EgyACGEB_O2 showing higher effectiveness. In addition, both P. kudriavzevii strains effectively controlled grey mold disease caused by B. cinerea in golden delicious apples, suggesting their potential as sustainable and eco-friendly biocontrol agents for post-harvest diseases. Based on a comprehensive bioinformatics pipeline, candidate-secreted proteins responsible for the potent antifungal activity of P. kudriavzevii were identified. A total of 59 proteins were identified as common among the P. kudriavzevii CBS573, SD108, and SD129 strains. Approximately 23% of the secreted proteins in the P. kudriavzevii predicted secretome are hydrolases with various activities, including proteases, lipases, glycosidases, phosphatases, esterases, carboxypeptidases, or peptidases. In addition, a set of cell-wall-related proteins was identified, which might enhance the biocontrol activity of P. kudriavzevii by preserving the structure and integrity of the cell wall. A papain inhibitor was also identified and could potentially offer a supplementary defense against plant pathogens.

CONCLUSION

Our results revealed the biocontrol capabilities of P. kudriavzevii against plant pathogenic fungi. The research focused on screening novel strains for their ability to inhibit the growth of common pathogens, both in vitro and in vivo. This study shed light on how P. kudriavzevii interacts with fungal pathogens. The findings can help develop effective strategies for managing plant diseases.

Highly efficient expression and secretion of human lysozyme using multiple strategies in Pichia pastoris

BACKGROUND

Human lysozyme (hLYZ), an emerging antibacterial agent, has extensive application in the food and pharmaceutical industries. However, the source of hLYZ is particularly limited.

RESULTS

To achieve highly efficient expression and secretion of hLYZ in Pichia pastoris, multiple strategies including G418 sulfate screening, signal sequence optimization, vacuolar sorting receptor VPS10 disruption, and chaperones/transcription factors co-expression were applied. The maximal enzyme activity of extracellular hLYZ in a shaking flask was 81,600 ± 5230 U mL-1 , which was about five times of original strain. To further reduce the cost, the optimal medium RDMY was developed and the highest hLYZ activity reached 352,000 ± 16,696.5 U mL-1 in a 5 L fermenter.

CONCLUSION

This research provides a very useful and cost-effective approach for the hLYZ production in P. pastoris and can also be applied to the production of other recombinant proteins.

Perspective: A proposal on solutions of modern supply chain construction for lactoferrin

Lactoferrin is an iron-binding glycoprotein of the transferrin family that is found in most bodily fluids of mammals and has a variety of biological and beneficial functions, with great importance in health enhancement as a supplement for humans and other animals. More than 300 t of lactoferrin were produced in 2021, and this number is expected to grow yearly by 10% to 12%, to over 580 t in 2030. With new and important functions of lactoferrin being revealed and studied, focus on its industrial production and application is increasing accordingly. However, lactoferrin is mainly sourced from cheese whey or skim milk by cation-exchange column chromatography, which is a costly and low-quality method. A potential solution for lactoferrin global supply chain construction is proposed in this article as a complement to traditional routes of purification from whey or skim milk. The large-scale production of lactoferrin, mainly by recombinant yeast, mammal, and grain systems, as well as the market niche and product design, are discussed.

Biosynthesis of High-Active Hemoproteins by the Efficient Heme-Supply Pichia Pastoris Chassis

Microbial synthesis of valuable hemoproteins has become a popular research topic, and Pichia pastoris is a versatile platform for the industrial production of recombinant proteins. However, the inadequate supply of heme limits the synthesis of high-active hemoproteins. Here a strategy for enhancing intracellular heme biosynthesis to improve the titers and functional activities of hemoproteins is reported. After selecting a suitable expressional strategy for globins, the efficient heme-supply P. pastoris chassis is established by removing the spatial segregation during heme biosynthesis, optimizing precursor synthesis, assembling rate-limiting enzymes using protein scaffolds, and inhibiting heme degradation. This robust chassis produces several highly active hemoproteins, including porcine myoglobin, soy hemoglobin, Vitreoscilla hemoglobin, and P450-BM3, which can be used in the development of artificial meat, high-cell-density fermentation, and whole-cell catalytic synthesis of high-value-added compounds. Furthermore, the engineered chassis strain has great potential for producing and applying other hemoproteins with high activities in various fields.

Bioconversion of C1 feedstocks for chemical production using Pichia pastoris

Bioconversion of C1 feedstocks for chemical production offers a promising solution to global challenges such as the energy and food crises and climate change. The methylotroph Pichia pastoris is an attractive host system for the production of both recombinant proteins and chemicals from methanol. Recent studies have also demonstrated its potential for utilizing CO2 through metabolic engineering or coupling with electrocatalysis. This review focuses on the bioconversion of C1 feedstocks for chemical production using P. pastoris. Herein the challenges and feasible strategies for chemical production in P. pastoris are discussed. The potential of P. pastoris to utilize other C1 feedstocks - including CO2 and formate - is highlighted, and new insights from the perspectives of synthetic biology and material science are proposed.

Full-length versus truncated α-factor secretory signal sequences for expression of recombinant human insulin precursor in yeast Pichia pastoris: a comparison

BACKGROUND

Human insulin was the first FDA-approved biopharmaceutical drug produced through recombinant DNA technology. The previous studies successfully expressed recombinant human insulin precursors (HIP) in Pichia pastoris truncated and full-length α-factor recombinant clones. The matting α-factor (Matα), a signal secretion, direct the HIP protein into the culture media. This study aimed to compare the HIP expression from full-length and truncated α-factor secretory signals clones that grown in two types of media, buffered methanol complex medium (BMMY) and methanol basal salt medium (BSMM).

RESULTS

ImageJ analysis of the HIP's SDS-PAGE shows that the average HIP expression level of the recombinant P. pastoris truncated α-factor clone (CL4) was significantly higher compared to the full-length (HF7) when expressed in both media. Western blot analysis showed that the expressed protein was the HIP. The α-factor protein structure was predicted using the AlphaFold and visualized using UCSF ChimeraX to confirm the secretion ability for both clones.

CONCLUSIONS

CL4 clone, which utilized a truncated α-factor in the P. pastoris HIP expression cassette, significantly expressed HIP 8.97 times (in BMMY) and 1.17 times (in BSMM) higher than HF7 clone, which used a full-length α-factor secretory signal. This research confirmed that deletion of some regions of the secretory signal sequence significantly improved the efficiency of HIP protein expression in P. pastoris.

Engineered Living Materials For Sustainability

Recent advances in synthetic biology and materials science have given rise to a new form of materials, namely engineered living materials (ELMs), which are composed of living matter or cell communities embedded in self-regenerating matrices of their own or artificial scaffolds. Like natural materials such as bone, wood, and skin, ELMs, which possess the functional capabilities of living organisms, can grow, self-organize, and self-repair when needed. They also spontaneously perform programmed biological functions upon sensing external cues. Currently, ELMs show promise for green energy production, bioremediation, disease treatment, and fabricating advanced smart materials. This review first introduces the dynamic features of natural living systems and their potential for developing novel materials. We then summarize the recent research progress on living materials and emerging design strategies from both synthetic biology and materials science perspectives. Finally, we discuss the positive impacts of living materials on promoting sustainability and key future research directions.

Synthetic biology-guided design and biosynthesis of protein polymers for delivery

Vehicles derived from genetically engineered protein polymers have gained momentum in the field of biomedical engineering due to their unique designability, remarkable biocompatibility and excellent biodegradability. However, the design and production of these protein polymers with on-demand sequences and supramolecular architectures remain underexplored, particularly from a synthetic biology perspective. In this review, we summarize the state-of-the art strategies for constructing the highly repetitive genes encoding the protein polymers, and highlight the advanced approaches for metabolically engineering expression hosts towards high-level biosynthesis of the target protein polymers. Finally, we showcase the typical protein polymers utilized to fabricate delivery vehicles.

Application of Collagen-Based Hydrogel in Skin Wound Healing

The repair of skin injury has always been a concern in the medical field. As a kind of biopolymer material with a special network structure and function, collagen-based hydrogel has been widely used in the field of skin injury repair. In this paper, the current research and application status of primal hydrogels in the field of skin repair in recent years are comprehensively reviewed. Starting from the structure and properties of collagen, the preparation, structural properties, and application of collagen-based hydrogels in skin injury repair are emphatically described. Meanwhile, the influences of collagen types, preparation methods, and crosslinking methods on the structural properties of hydrogels are emphatically discussed. The future and development of collagen-based hydrogels are prospected, which is expected to provide reference for the research and application of collagen-based hydrogels for skin repair in the future.

Recombinant protein-based injectable materials for biomedical applications

Injectable nanocarriers and hydrogels have found widespread use in a variety of biomedical applications such as local and sustained biotherapeutic cargo delivery, and as cell-instructive matrices for tissue engineering. Recent advances in the development and application of recombinant protein-based materials as injectable platforms under physiological conditions have made them useful platforms for the development of nanoparticles and tissue engineering matrices, which are reviewed in this work. Protein-engineered biomaterials are highly customizable, and they provide distinctly tunable rheological properties, encapsulation efficiencies, and delivery profiles. In particular, the key advantages of emerging technologies which harness the stimuli-responsive properties of recombinant polypeptide-based materials are highlighted in this review.

Influence of Long-Term Agar-Slant Preservation at 4 °C on the Recombinant Enzyme Activity of Engineered Yeast

Strain preservation to maintain stable vitality and the recombinant enzyme activity plays a crucial role in industrial fermentation. A Pichia pastoris strain is routinely stored at −80 °C in a glycerol vial and activated on an antibiotic-containing YPD agar plate before being used for fermentation. Alternatively, the activated strain should be preserved in the agar slant at 2~4 °C (low-temperature storage) for a short period before use. To maximize the utilization of the low-temperature storage for fermentation, we evaluated this method by observing the capacity of both the vitality and the recombinant enzyme activity of the strain at different preservation durations. We found that engineered yeast could be preserved by low-temperature storage for at least 30 months without losing its vitality and biomass enzyme activity by the end of fermentation and could be directly used for the seed cultivation of fermentation, which is more time-saving than strain recovery from −80 °C in a glycerol vial. Moreover, the antibiotic added to the agar slant could be omitted if the heterologous gene was integrated into the host chromosome. Our approach may greatly elevate the production efficiency of the strain.

C1-based biomanufacturing: Advances, challenges and perspectives

One-carbon (C1) compounds have emerged as a key research focus due to the growth of metabolic engineering and synthetic biology as affordable and sustainable nonfood sugar feedstocks for energy-efficient and environmentally friendly biomanufacturing. This paper summarizes and discusses current developments in C1 compounds for biomanufacturing. First, two primary groups of microbes that use C1 compounds (native and synthetic) are introduced, and the traits, categorization, and functions of C1 microbes are summarized. Second, engineering strategies for C1 utilization are compiled and reviewed, including reconstruction of C1-utilization pathway, enzyme engineering, cofactor engineering, genome-scale modeling, and adaptive laboratory evolution. Third, a review of C1 compounds' uses in the synthesis of biofuels and high-value compounds is presented. Finally, potential obstacles to C1-based biomanufacturing are highlighted along with future research initiatives.

Transcription regulation strategies in methylotrophs: progress and challenges

As a promising industrial microorganism, methylotroph is capable of using methane or methanol as the sole carbon source natively, which has been utilized in the biosynthesis of various bioproducts. However, the relatively low efficiency of carbon conversion has become a limiting factor throughout the development of methanotrophic cell factories due to the unclear genetic background. To better highlight their advantages in methane or methanol-based biomanufacturing, some metabolic engineering strategies, including upstream transcription regulation projects, are being popularized in methylotrophs. In this review, several strategies of transcription regulations applied in methylotrophs are summarized and their applications are discussed and prospected.

High-efficiency secretory expression and characterization of the recombinant type III human-like collagen in Pichia pastoris

Collagen, the highest content protein in the body, has irreplaceable biological functions, and it is widespread concerned in food, beauty, and medicine with great market demand. The gene encoding the recombinant type III human-like collagen α1 chain fragment was integrated into P. pastoris genome after partial amino acids were substituted. Combined with promoter engineering and high-density fermentation technology, soluble secretory expression with the highest yield of 1.05 g L-1 was achieved using two-stage feeding method, and the purity could reach 96% after affinity purification. The determination of N/C-terminal protein sequence were consistent with the theoretical expectation and showed the characteristics of Gly-X-Y repeated short peptide sequence. In amino acid analysis, glycine shared 27.02% and proline 23.92%, which were in accordance with the characteristics of collagen. Ultraviolet spectrum combined with Fourier transform infrared spectroscopy as well as mass spectrometry demonstrated that the target product conformed to the characteristics of collagen spectrums and existed as homologous dimer and trimer in the broth. This work provided a sustainable and economically viable source of the recombinant type III human-like collagen.

Synthetic methylotrophic yeasts for the sustainable fuel and chemical production

Global energy-related emissions, in particular carbon dioxide, are rapidly increasing. Without immediate and strong reductions across all sectors, limiting global warming to 1.5 °C and thus mitigating climate change is beyond reach. In addition to the expansion of renewable energies and the increase in energy efficiency, the so-called Carbon Capture and Utilization technologies represent an innovative approach for closing the carbon cycle and establishing a circular economy. One option is to combine CO₂ capture with microbial C₁ fermentation. C₁-molecules, such as methanol or formate are considered as attractive alternative feedstock for biotechnological processes due to their sustainable production using only CO₂, water and renewable energy. Native methylotrophic microorganisms can utilize these feedstock for the production of value-added compounds. Currently, constraints exist regarding the understanding of methylotrophic metabolism and the available genetic engineering tools are limited. For this reason, the development of synthetic methylotrophic cell factories based on the integration of natural or artificial methanol assimilation pathways in biotechnologically relevant microorganisms is receiving special attention. Yeasts like Saccharomyces cerevisiae and Yarrowia lipolytica are capable of producing important products from sugar-based feedstock and the switch to produce these in the future from methanol is important in order to realize a CO₂-based economy that is independent from land use. Here, we review historical biotechnological applications, the metabolism and the characteristics of methylotrophic yeasts. Various studies demonstrated the production of a broad set of promising products from fine chemicals to bulk chemicals by applying methylotrophic yeasts. Regarding synthetic methylotrophy, the deep understanding of the methylotrophic metabolism serves as the basis for microbial strain engineering and paves the way towards a CO₂-based circular bioeconomy. We highlight design aspects of synthetic methylotrophy and discuss the resulting chances and challenges using non-conventional yeasts as host organisms. We conclude that the road towards synthetic methylotrophic yeasts can only be achieved through a combination of methods (e.g., metabolic engineering and adaptive laboratory evolution). Furthermore, we presume that the installation of metabolic regeneration cycles such as supporting carbon re-entry towards the pentose phosphate pathway from C₁-metabolism is a pivotal target for synthetic methylotrophy.

Whole Genome Sequencing Analysis of Effects of CRISPR/Cas9 in Komagataella phaffii: A Budding Yeast in Distress

The industrially important non-conventional yeast Komagataella phaffii suffers from low rates of homologous recombination, making site specific genetic engineering tedious. Therefore, genome editing using CRISPR/Cas represents a simple and efficient alternative. To characterize on- and off-target mutations caused by CRISPR/Cas9 followed by non-homologous end joining repair, we chose a diverse set of CRISPR/Cas targets and conducted whole genome sequencing on 146 CRISPR/Cas9 engineered single colonies. We compared the outcomes of single target CRISPR transformations to double target experiments. Furthermore, we examined the extent of possible large deletions by targeting a large genomic region, which is likely to be non-essential. The analysis of on-target mutations showed an unexpectedly high number of large deletions and chromosomal rearrangements at the CRISPR target loci. We also observed an increase of on-target structural variants in double target experiments as compared to single target experiments. Targeting of two loci within a putatively non-essential region led to a truncation of chromosome 3 at the target locus in multiple cases, causing the deletion of 20 genes and several ribosomal DNA repeats. The identified de novo off-target mutations were rare and randomly distributed, with no apparent connection to unspecific CRISPR/Cas9 off-target binding sites.

Antiviral activity of mink interferon alpha expressed in the yeast Pichia pastoris

Many viruses can cause infections in mink, including canine distemper virus, mink enteritis virus, and Aleutian disease virus. Current treatments are ineffective, and these infections are often fatal, causing severe economic losses. As antiviral drugs may effectively prevent and control these infections, recent research has increasingly focused on antiviral interferons. Herein, the gene encoding a mature mink interferon alpha (MiIFN-α) was synthesized according to the P. pastoris preference of codon usage and a recombinant plasmid, pPICZαA-MiIFN-α, was constructed. pPICZαA-MiIFN-α was linearized and transformed into the P. pastoris X33 strain, and zeocin-resistant transformants were selected. Protein expression was induced by methanol. SDS-PAGE and western blot analyses showed that a 25-kDa fusion protein was expressed in the culture supernatant. Antiviral activity of the expressed protein was determined using cytopathic effect inhibition (CPEI). The purified MiIFN-α significantly inhibited the cytopathic effect of vesicular stomatitis virus with a green fluorescent protein (VSV-GFP) in F81 feline kidney cells, with an antiviral activity of 6.4 × 10⁷ IU/mL; it also significantly inhibited MEV replication in F81 cells. MiIFN-α antiviral activity against VSV-GFP was significantly reduced on treatment with pH 4 and pH 10 conditions for 24 h (p < 0.01). Serum MiIFN-α concentrations in rat were measured using enzyme-linked immune-sorbent assay; MiIFN-α concentrations in rat serum peaked at ~36 h after injection. A high dose of MiIFN-α was safe for use. There were no significant differences in body temperature, tissue changes, and lymphocyte, total white blood cell, and central granulocyte counts between the injected and control groups (p > 0.05). These findings lay a foundation for the large-scale production of recombinant MiIFNs.

Pushing and pulling proteins into the yeast secretory pathway enhances recombinant protein secretion

Yeasts and especially Pichia pastoris (syn Komagataella spp.) are popular microbial expression systems for the production of recombinant proteins. One of the key advantages of yeast host systems is their ability to secrete the recombinant protein into the culture media. However, secretion of some recombinant proteins is less efficient. These proteins include antibody fragments such as Fabs or scFvs. We have recently identified translocation of nascent Fab fragments from the cytosol into the endoplasmic reticulum (ER) as one major bottleneck. Conceptually, this bottleneck requires engineering to increase the flux of recombinant proteins at the translocation step by pushing on the cytosolic side and pulling on the ER side. This engineering strategy is well-known in the field of metabolic engineering. To apply the push-and-pull strategy to recombinant protein secretion, we chose to modulate the cytosolic and ER Hsp70 cycles, which have a key impact on the translocation process. After identifying the relevant candidate factors of the Hsp70 cycles, we combined the push-and-pull factors in a single strain and achieved synergistic effects for antibody fragment secretion. With this concept we were able to successfully engineer strains and improve protein secretion up to 5-fold for different model protein classes. Overall, titers of more than 1.3 g/L Fab and scFv were reached in bioreactor cultivations.

Pathway engineering facilitates efficient protein expression in Pichia pastoris

Pichia pastoris has been recognized as an important platform for the production of various heterologous proteins in recent years. The strong promoter AOX1, induced by methanol, with the help of the α-pre-pro signal sequence, can lead to a high expression level of extracellular protein. However, this combination was not always efficient, as protein secretion in P. pastoris involves numerous procedures mediated by several cellular proteins, including folding assisted by endoplasmic reticulum (ER) molecular chaperones, degradation through ubiquitination, and an efficient vesicular transport system. Efficient protein expression requires the cooperation of various intracellular pathways. This article summarizes the process of protein secretion, modification, and transportation in P. pastoris. In addition, the roles played by the key proteins in these processes and the corresponding co-expression effects are also listed. It is expected to lay the foundation for the industrial protein production of P. pastoris. KEY POINTS: • Mechanisms of chaperones in protein folding and their co-expression effects are summarized. • Protein glycosylation modifications are comprehensively reviewed. • Current dilemmas in the overall protein secretion pathway of Pichia pastoris and corresponding solutions are demonstrated.

Bioengineering of spider silks for the production of biomedical materials

Spider silks are well known for their extraordinary mechanical properties. This characteristic is a result of the interplay of composition, structure and self-assembly of spider silk proteins (spidroins). Advances in synthetic biology have enabled the design and production of spidroins with the aim of biomimicking the structure-property-function relationships of spider silks. Although in nature only fibers are formed from spidroins, in vitro, scientists can explore non-natural morphologies including nanofibrils, particles, capsules, hydrogels, films or foams. The versatility of spidroins, along with their biocompatible and biodegradable nature, also placed them as leading-edge biological macromolecules for improved drug delivery and various biomedical applications. Accordingly, in this review, we highlight the relationship between the molecular structure of spider silk and its mechanical properties and aims to provide a critical summary of recent progress in research employing recombinantly produced bioengineered spidroins for the production of innovative bio-derived structural materials.

Identification and characterization of sericin5 reveals non-cocoon silk sericin components with high β-sheet content and adhesive strength

Sericins are glue proteins on the surface of silk fibers. Four sericins have been characterized in silkworm, namely sericin1 (Ser1), sericin2 (Ser2), sericin3 (Ser3), and sericin4 (Ser4). In this study, we report a novel sericin, sericin5 (Ser5), which exists only in non-cocoon silk. We describe the sequence, exon-intron structure, and translation products of Ser5 in Bombyx mori. The Ser5 gene is approximately 22-kb long and comprises 16 exons. Ser5 protein has a size of 260 kDa, as determined by SDS-PAGE, western blot, and LC-MS/MS. Immunofluorescence analysis revealed that Ser5 co-localizes with Ser1 in the sericin layer. The expression pattern of Ser5 was detected at the transcriptional and translational levels. We systematically analyzed and compared the amino acid composition, repeat regions, and hydrophilicity of silkworm sericins. Morphological observations showed that non-cocoon silk had more sericin than cocoon silk. Circular dichroism spectra revealed that non-cocoon silk sericin contained more β-sheet structures than cocoon silk sericin. In addition, we found that the hydrophilicity and adhesive strength of native sericin increases gradually from the inner layer to the outer layer. This research enhances our understanding of various sericins from cocoon silk and non-cocoon silk with regard to their expression patterns, hydrophilicity, secondary structure and adhesive performances. STATEMENT OF SIGNIFICANCE: : Sericin is a natural biomaterial with diverse biological properties, which has long been used as tissue engineering and biomedical applications. However, the composition and distribution of sericins in different kinds of silk are still uncertain, and the properties difference between sericins have not yet been reported. Our study makes a significant contribution to the literature as it identifies the sequence, composition, hydrophilicity and adhesive property of sericins. Moreover, it provides key insights into the structure-function and function-distribution relationships associated with sericins. We believe that this study will arouse the interest to the readership of your journal as it identifies the new complete sequence of sericin and revealed the composition and properties of sericin, thus highlighting their future potentials applications in both the biomaterial and technical fields.

Expanding the promoter toolbox for metabolic engineering of methylotrophic yeasts

Methylotrophic yeasts have been widely recognized as a promising host for production of recombinant proteins and value-added chemicals. Promoters for controlled gene expression are critical for construction of efficient methylotrophic yeasts cell factories. Here, we summarized recent advances in characterizing and engineering promoters in methylotrophic yeasts, such as Komagataella phaffii and Ogataea polymorpha. Constitutive and inducible promoters controlled by methanol or other inducers/repressors were introduced to demonstrate their applications in production of proteins and chemicals. Furthermore, efforts of promoter engineering, including site-directed mutagenesis, hybrid promoter, and transcription factor regulation to expand the promoter toolbox were also summarized. This mini-review also provides useful information on promoters for the application of metabolic engineering in methylotrophic yeasts. KEY POINTS: • The characteristics of six methylotrophic yeasts and their promoters are described. • The applications of Komagataella phaffii and Ogataea polymorpha in metabolic engineeringare expounded. • Three promoter engineering strategies are introduced in order to expand the promoter toolbox.

Recombinant Spider Silk: Promises and Bottlenecks

Spider silk threads have exceptional mechanical properties such as toughness, elasticity and low density, which reach maximum values compared to other fibre materials. They are superior even compared to Kevlar and steel. These extraordinary properties stem from long length and specific protein structures. Spider silk proteins can consist of more than 20,000 amino acids. Polypeptide stretches account for more than 90% of the whole protein, and these domains can be repeated more than a hundred times. Each repeat unit has a specific function resulting in the final properties of the silk. These properties make them attractive for innovative material development for medical or technical products as well as cosmetics. However, with livestock breeding of spiders it is not possible to reach high volumes of silk due to the cannibalistic behaviour of these animals. In order to obtain spider silk proteins (spidroins) on a large scale, recombinant production is attempted in various expression systems such as plants, bacteria, yeasts, insects, silkworms, mammalian cells and animals. For viable large-scale production, cost-effective and efficient production systems are needed. This review describes the different types of spider silk, their proteins and structures and discusses the production of these difficult-to-express proteins in different host organisms with an emphasis on plant systems.

A novel recombinant chimeric bio-adhesive protein consisting of mussel foot protein 3, 5, gas vesicle protein A, and CsgA curli protein expressed in Pichia pastoris

Despite various efforts to produce potent recombinant bio-adhesive proteins for medical purposes, efficient production of a safe and feasible bio-glue is not yet a commercial reality due to the weak properties or low expression levels. Here, a feasible expression system has been developed to produce strong recombinant fusion bioinspired protein using mussel foot protein 3 and 5 (Mfps) along with gas vesicle protein A (GvpA) of Anabaena flos-aquae, and a curli protein CsgA from E. coli, expressed under the control of alcohol oxidase (AOX1) promoter for high-level production in yeast P. pastoris using pPICZα vector. Purified chimeric proteins were first evaluated using western blotting, and their remaining dihydroxyphenylalanine (DOPA) was measured in the modified proteins by NBT assay. We further elucidated the mechanistic properties of obtained adhesive protein assembly in various pH levels based on its different subunits using atomic force microscopy (AFM) when adsorbed onto the mica surface. We found that both combinational structural features of subunits and post-translational changes during expression in yeast host have led to potent adherence due to higher DOPA residues specially in acidic condition and tetrad complex which is higher than that of earlier reports in prokaryotic systems. We believe that our obtained chimeric protein resulted from the fusion of GvpA and CsgA proteins with DOPA-containing Mfp proteins, expressed in the methylotrophic yeast, P. pastoris, not only presents a candidate for future biomedical applications but also provides novel biological clues used for high-performance bioinspired biomaterial designation.

Can recombinant milk proteins replace those produced by animals?

The consumption of animal proteins in general, and dairy proteins in particular, is associated with sustainability and animal welfare issues. Recombinant synthesis of milk proteins is therefore receiving increasing interest, with several studies showing synthesis of milk proteins using a wide range of expression systems. Achieving a high yield and purity is essential for economic production. Besides the synthesis, also the construction of the specific structure in which milk proteins are present in animal milks, casein micelles, is needed. Looking at the current state-of-the-art, the steps to produce recombinant dairy products are technically feasible, but whether it can be implemented at low cost, with the process being environmentally friendly, remains to be seen in the coming years.

What makes Komagataella phaffii non-conventional?

The important industrial protein production host Komagataella phaffii (syn Pichia pastoris) is classified as a non-conventional yeast. But what exactly makes K. phaffii non-conventional? In this review, we set out to address the main differences to the 'conventional' yeast Saccharomyces cerevisiae, but also pinpoint differences to other non-conventional yeasts used in biotechnology. Apart from its methylotrophic lifestyle, K. phaffii is a Crabtree-negative yeast species. But even within the methylotrophs, K. phaffii possesses distinct regulatory features such as glycerol-repression of the methanol-utilization pathway or the lack of nitrate assimilation. Rewiring of the transcriptional networks regulating carbon (and nitrogen) source utilization clearly contributes to our understanding of genetic events occurring during evolution of yeast species. The mechanisms of mating-type switching and the triggers of morphogenic phenotypes represent further examples for how K. phaffii is distinguished from the model yeast S. cerevisiae. With respect to heterologous protein production, K. phaffii features high secretory capacity but secretes only low amounts of endogenous proteins. Different to S. cerevisiae, the Golgi apparatus of K. phaffii is stacked like in mammals. While it is tempting to speculate that Golgi architecture is correlated to the high secretion levels or the different N-glycan structures observed in K. phaffii, there is recent evidence against this. We conclude that K. phaffii is a yeast with unique features that has a lot of potential to explore both fundamental research questions and industrial applications.

Microbial protein cell factories fight back?

The biopharmaceutical market is growing faster than ever, with two production systems competing for market dominance: mammalian cells and microorganisms. In recent years, based on the rise of antibody-based therapies, new biotherapeutic approvals have favored mammalian hosts. However, not only has extensive research elevated our understanding of microbes to new levels, but emerging therapeutic molecules also facilitate their use; thus, is it time for microbes to fight back? In this review, we answer this timely question by cross-comparing four microbial production hosts and examining the innovations made to both their secretion and post-translational modification (PTM) capabilities. Furthermore, we discuss the impact of tools, such as omics and systems biology, as well as alternative production systems and emerging biotherapeutics.

Modifications in the Kex2 P1' cleavage site in the α-MAT secretion signal lead to higher production of human granulocyte colony-stimulating factor in Pichia pastoris

The human granulocyte colony-stimulating factor (G-CSF) is one of the hematopoietic growth factors administered for chemotherapy induced neutropenia and is currently produced through recombinant route in Escherichia coli. The methylotrophic unicellular yeast Pichia pastoris (syn. Komagataella phaffii) makes a good host for production of human therapeutics as the proteins are low-mannose glycosylated, disulfide bonded and correctly folded on their way to the cell exterior. Given the low level of production of G-CSF in P. pastoris, the present study examined modification of the Saccharomyces cerevisiae derived α-mating type secretory signal sequence to enhance its production. The substitution of Glu, at the P1' position of the Kex2 cleavage site, by Val/Ala led to extracellular production of ~ 60 mg/L of G-CSF in the extracellular medium. Production was further increased to ~ 100 mg/L by putting these mutations against rarely occurring methanol slow utilization P. pastoris X-33 host. Analysis of the modelled structure of the signal peptide indicated exposed loop structures, created by presence of Val/Ala, that favour cleavage by the Kex2 peptidase thereby leading to enhanced production of G-CSF. The conformational changes, induced on account of binding between the signal sequence and the cargo protein (G-CSF), also appear to play an important role in the final yield of the extracellular protein.

Pichia pastoris (Komagataella phaffii) as a Cost-Effective Tool for Vaccine Production for Low- and Middle-Income Countries (LMICs)

Vaccination is of paramount importance to global health. With the advent of the more recent pandemics, the urgency to expand the range has become even more evident. However, the potential limited availability and affordability of vaccines to resource low- and middle-income countries has created a need for solutions that will ensure cost-effective vaccine production methods for these countries. Pichia pastoris (P. pastoris) (also known as Komagataella phaffii) is one of the most promising candidates for expression of heterologous proteins in vaccines development. It combines the speed and ease of highly efficient prokaryotic platforms with some key capabilities of mammalian systems, potentially reducing manufacturing costs. This review will examine the latest developments in P. pastoris from cell engineering and design to industrial production systems with focus on vaccine development and with reference to specific key case studies.

Recombinant active Peptides and their Therapeutic functions

Recombinant active peptides are utilized as diagnostic and biotherapeutics in various maladies and as bacterial growth inhibitors in the food industry. This consequently stimulated the need for recombinant peptides' production, which resulted in about 19 approved biotech peptides of 1-100 amino acids commercially available. While most peptides have been produced by chemical synthesis, the production of lengthy and complicated peptides comprising natural amino acids has been problematic with low quantity. Recombinant peptide production has become very vital, cost-effective, simple, environmentally friendly with satisfactory yields. Several reviews have focused on discussing expression systems, advantages, disadvantages, and alternatives strategies. Additionally, the information on the antimicrobial activities and other functions of multiple recombinant peptides is challenging to access and is scattered in literature apart from the food and drug administration (FDA) approved ones. From the reports that come to our knowledge, there is no existing review that offers substantial information on recombinant active peptides developed by researchers and their functions. This review provides an overview of some successfully produced recombinant active peptides of ≤100 amino acids by focusing on their antibacterial, antifungal, antiviral, anticancer, antioxidant, antimalarial, and immune-modulatory functions. It also elucidates their modes of expression that could be adopted and applied in future investigations. We expect that the knowledge available in this review would help researchers involved in recombinant active peptide development for therapeutic uses and other applications.

Targeted Deletion of Los1 Homologue Affects the Production of a Recombinant Model Protein in Pichia pastoris

Background:

The methylotrophic yeast Pichia pastoris is an appealing production host for a variety of recombinant proteins, including biologics. In this sense, various genetic- and non-genetic-based techniques have been implemented to improve the production efficiency of this expression platform. Los1 (loss of supression) encodes a non-essential nuclear tRNA exporter in Saccharomyces cerevisiae, which its deletion extends RLS. Herein, a los1-deficient strain of P. pastoris was generated and characterized.

Methods:

A gene disruption cassette was prepared and transformed into an anti-CD22-expressing strain of P. pastoris. A δ los1 mutant was isolated and confirmed. The drug sensitivity of the mutant was also assessed. The growth pattern and the level of anti-CD22 ScFv expression were compared between the parent and mutant strains.

Results:

The los1 homologue was found to be a non-essential gene in P. pastoris. Furthermore, the susceptibility of los1 deletion strain to protein synthesis inhibitors was altered. This strain showed an approximately 1.85-fold increase in the extracellular level of anti-CD22 scFv (p < 0.05). The maximum concentrations of total proteins secreted by δ los1 and parent strains were 125 mg/L and 68 mg/L, respectively.

Conclusion:

The presented data suggest that the targeted disruption of los1 homologue in P. pastoris can result in a higher expression level of our target protein. Findings of this study may improve the current strategies used in optimizing the productivity of recombinant P. pastoris strains.

Recent developments in sustainably sourced protein-based biomaterials

Research into the development of sustainable biomaterials is increasing in both interest and global importance due to the increasing demand for materials with decreased environmental impact. This research field utilises natural, renewable resources to develop innovative biomaterials. The development of sustainable biomaterials encompasses the entire material life cycle, from desirable traits, and environmental impact from production through to recycling or disposal. The main objective of this review is to provide a comprehensive definition of sustainable biomaterials and to give an overview of the use of natural proteins in biomaterial development. Proteins such as collagen, gelatin, keratin, and silk, are biocompatible, biodegradable, and may form materials with varying properties. Proteins, therefore, provide an intriguing source of biomaterials for numerous applications, including additive manufacturing, nanotechnology, and tissue engineering. We give an insight into current research and future directions in each of these areas, to expand knowledge on the capabilities of sustainably sourced proteins as advanced biomaterials.

Engineered yeast genomes accurately assembled from pure and mixed samples

Yeast whole genome sequencing (WGS) lacks end-to-end workflows that identify genetic engineering. Here we present Prymetime, a tool that assembles yeast plasmids and chromosomes and annotates genetic engineering sequences. It is a hybrid workflow-it uses short and long reads as inputs to perform separate linear and circular assembly steps. This structure is necessary to accurately resolve genetic engineering sequences in plasmids and the genome. We show this by assembling diverse engineered yeasts, in some cases revealing unintended deletions and integrations. Furthermore, the resulting whole genomes are high quality, although the underlying assembly software does not consistently resolve highly repetitive genome features. Finally, we assemble plasmids and genome integrations from metagenomic sequencing, even with 1 engineered cell in 1000. This work is a blueprint for building WGS workflows and establishes WGS-based identification of yeast genetic engineering.

Environmental biodegradability of recombinant structural protein

Next generation polymers needs to be produced from renewable sources and to be converted into inorganic compounds in the natural environment at the end of life. Recombinant structural protein is a promising alternative to conventional engineering plastics due to its good thermal and mechanical properties, its production from biomass, and its potential for biodegradability. Herein, we measured the thermal and mechanical properties of the recombinant structural protein BP1 and evaluated its biodegradability. Because the thermal degradation occurs above 250 °C and the glass transition temperature is 185 °C, BP1 can be molded into sheets by a manual hot press at 150 °C and 83 MPa. The flexural strength and modulus of BP1 were 115 ± 6 MPa and 7.38 ± 0.03 GPa. These properties are superior to those of commercially available biodegradable polymers. The biodegradability of BP1 was carefully evaluated. BP1 was shown to be efficiently hydrolyzed by some isolated bacterial strains in a dispersed state. Furthermore, it was readily hydrolyzed from the solid state by three isolated proteases. The mineralization was evaluated by the biochemical oxygen demand (BOD)-biodegradation testing with soil inocula. The BOD biodegradability of BP1 was 70.2 ± 6.0 after 33 days.

Improved production of recombinant Rhizomucor miehei lipase by coexpressing protein folding chaperones in Pichia pastoris, which triggered ER stress

Rhizomucor miehei lipase (RML) is a biocatalyst that widely used in laboratory and industrial. Previously, RML with a 70-amino acid propeptide (pRML) was cloned and expressed in P. pastoris. Recombinant strains with (strain containing 4-copy prml) and without ER stress (strain containing 2-copy prml) were obtained. However, the effective expression of pRML in P. pastoris by coexpressing ER-related elements in pRML-produced strain with or without ER stress has not been reported to date. In this study, an efficient way to produce functional pRML was explored in P. pastoris. The coexpression of protein folding chaperones, including PDI and ERO1, in different strains with or without ER stress, was investigated. PDI overexpression only increased pRML production in 4-copy strain from 705 U/mL to 1430 U/mL because it alleviated the protein folded stress, increased the protein concentration from 0.56  mg/mL to 0.65 mg/mL, and improved enzyme-specific activity from 1238 U/mg to 2186 U/mg. However, PDI coexpression could not improve pRML production in the 2-copy strain because it increased protein folded stress, while ERO1 coexpression in the two strains all had a negative effect on pRML expression. We also investigated the effect of the propeptide on the substrate specificity and the condition for pRML enzyme powder preparation. Results showed that the relative activity exceeded 80% when the substrates C8–C10 were detected at 35°C and pH 6, and C8–C12 at 45°C and pH 8. The optimal enzyme powder preparation pH was 7, and the maximum recovery rate for pRML was 73.19%.

Schistosoma japonicum cathepsin B2 (SjCB2) facilitates parasite invasion through the skin

Cercariae invasion of the human skin is the first step in schistosome infection. Proteases play key roles in this process. However, little is known about the related hydrolytic enzymes in Schistosoma japonicum. Here, we investigated the biochemical features, tissue distribution and biological roles of a cathepsin B cysteine protease, SjCB2, in the invasion process of S. japonicum cercariae. Enzyme activity analysis revealed that recombinant SjCB2 is a typical cysteine protease with optimum temperature and pH for activity at 37°C and 4.0, respectively, and can be totally inhibited by the cysteine protease inhibitor E-64. Immunoblotting showed that both the zymogen (50 kDa) and mature enzyme (30.5 kDa) forms of SjCB2 are expressed in the cercariae. It was observed that SjCB2 localized predominantly in the acetabular glands and their ducts of cercariae, suggesting that the protease could be released during the invasion process. The protease degraded collagen, elastin, keratin, fibronectin, immunoglobulin (A, G and M) and complement C3, protein components of the dermis and immune system. In addition, proteomic analysis demonstrated that SjCB2 can degrade the human epidermis. Furthermore, it was showed that anti-rSjCB2 IgG significantly reduced (22.94%) the ability of the cercariae to invade the skin. The cysteine protease, SjCB2, located in the acetabular glands and their ducts of S. japonicum cercariae. We propose that SjCB2 facilitates skin invasion by degrading the major proteins of the epidermis and dermis. However, this cysteine protease may play additional roles in host-parasite interaction by degrading immunoglobins and complement protein.

Schistosomiasis is one of the most prevalent parasitic diseases in the world, with about 200 million humans infected in 74 tropical countries. The infection of schistosome is initiated when the larvae, cercariae, penetrate the human skin. Proteolytic enzymes are likely involved in the invasion process, but these have yet to be characterized for S. japonicum. Here, we have functionally expressed a recombinant form of the cathepsin B cysteine protease SjCB2 in the yeast Pichia pastoris. Our study showed that SjCB2 degraded a number of proteins associated with the skin and immune systems, and disrupted the structure of the human epidermis. The enzyme was located in the acetabular glands and their ducts in the cercariae, where it would be stored before released into the skin. Antibody-blocking studies revealed that SjCB2 had a 22.94% contribution during the cercariae invasion process. Taken together, our findings suggest that SjCB2 helped cercariae penetrating the skin barrier and evading the immune attack to allow successful infection in the mammalian host.

Bioengineered elastin- and silk-biomaterials for drug and gene delivery

Advances in medical science have led to diverse new therapeutic modalities, as well as enhanced understanding of the progression of various disease states. These findings facilitate the design and development of more customized and exquisite drug delivery systems that aim to improve therapeutic indices of drugs to treat a variety of conditions. Synthetic polymer-based drug carriers have often been the focus of such research. However, these structures suffer from challenges with heterogeneity of the starting material, limited chemical features, complex functionalization methods, and in some cases a lack of biocompatibility. Consequently, protein-based polymers have garnered much attention in recent years due to their monodisperse features, ease of production and functionalization, and biocompatibility. Genetic engineering techniques enable the advancement of protein-based drug delivery systems with finely tuned physicochemical properties, and thus an expanded level of customization unavailable with synthetic polymers. Of these genetically engineered proteins, elastin-like proteins (ELP), silk-like proteins (SLP), and silk-elastin-like proteins (SELP) provide a unique set of alternatives for designing drug delivery systems due to their inherent chemical and physical properties and ease of engineering afforded by recombinant DNA technologies. In this review we examine the advantages of genetically engineered drug delivery systems with emphasis on ELP and SLP constructions. Methods for fabrication and relevant biomedical applications will also be discussed.

Metabolic engineering of Pichia pastoris for malic acid production from methanol

The application of rational design in reallocating metabolic flux to accumulate desired chemicals is always restricted by the native regulatory network. In this study, recombinant Pichia pastoris was constructed for malic acid production from sole methanol through rational redistribution of metabolic flux. Different malic acid accumulation modules were systematically evaluated and optimized in P. pastoris. The recombinant PP-CM301 could produce 8.55 g/L malic acid from glucose, which showed a 3.45-fold increase compared to the parent strain. To improve the efficiency of site-directed gene knockout, NHEJ-related protein Ku70 was destroyed, whereas leading to the silencing of heterogenous genes. Hence, genes related to by-product generation were deleted via a specially designed FRT/FLP system, which successfully reduced succinic acid and ethanol production. Furthermore, a key node in the methanol assimilation pathway, glucose-6-phosphate isomerase was knocked out to liberate metabolic fluxes trapped in the XuMP cycle, which finally enabled 2.79 g/L malic acid accumulation from sole methanol feeding with nitrogen source optimization. These results will provide guidance and reference for the metabolic engineering of P. pastoris to produce value-added chemicals from methanol.

Recombinant Protein Polymers: A Coming Wave of Personal Care Ingredients

After decades of research and development, recombinant protein polymers have begun to find applications outside the pharmaceutical and biomedical fields. Several recombinant derivatives of natural structural proteins are now being sold in personal care products, providing novel functionality while also being animal-free, not derived from petroleum, biocompatible, and biodegradable. Consumers are now demanding these material characteristics in their personal care products, and a backlog of well-characterized recombinant protein polymers could become the future of personal care ingredients.