Paving the way for the production of secretory proteins by yeast cell factories

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.

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.

In vivo enzymatic digestion of HRV 3C protease cleavage sites-containing proteins produced in a silkworm-baculovirus expression system

Baculovirus expression vector system (BEVS) has been recognized as a potent protein expression system in engineering valuable enzymes and vaccines. Various fusion tags facilitate protein purification, leaving the potential risk to influence the target protein's biological activity negatively. It is of great interest to consider removing the additional tags using site-specific proteases, such as human rhinoviruses (HRV) 3C protease. The current study validated the cleavage activity of 3C protease in Escherichia coli and silkworm-BEVS systems by mixing the cell or fat body lysates of 3C protein and 3C site containing target protein in vitro. Further verification has been performed in the fat body lysate from co-expression of both constructs, showing remarkable cleavage efficiency in vivo silkworm larvae. We also achieved the glutathione-S-transferase (GST) tag-cleaved product of the VP15 protein from the White spot syndrome virus after purification, suggesting that we successfully established a coinfection-based recognition-and-reaction BEVS platform for the tag-free protein engineering.

Recombinant Protein Production and Purification of Insoluble Proteins

Proteins are synthesized in heterologous systems because of the impossibility to obtain satisfactory yields from natural sources. The efficient production of soluble and functional recombinant proteins is among the main goals in the biotechnological field. In this context, it is important to point out that under stress conditions, protein folding machinery is saturated and this promotes protein misfolding and, consequently, protein aggregation. Thus, the selection of the optimal expression organism and its growth conditions to minimize the formation of insoluble protein aggregates should be done according to the protein characteristics and downstream requirements. Escherichia coli is the most popular recombinant protein expression system despite the great development achieved so far by eukaryotic expression systems. Besides, other prokaryotic expression systems, such as lactic acid bacteria and psychrophilic bacteria, are gaining interest in this field. However, it is worth mentioning that prokaryotic expression system poses, in many cases, severe restrictions for a successful heterologous protein production. Thus, eukaryotic systems such as mammalian cells, insect cells, yeast, filamentous fungus, and microalgae are an interesting alternative for the production of these difficult-to-express proteins.

Heterologous production of cellulose- and starch-degrading hydrolases to expand Saccharomyces cerevisiae substrate utilization: Lessons learnt

Selected strains of Saccharomyces cerevisiae are used for commercial bioethanol production from cellulose and starch, but the high cost of exogenous enzymes for substrate hydrolysis remains a challenge. This can be addressed through consolidated bioprocessing (CBP) where S. cerevisiae strains are engineered to express recombinant glycoside hydrolases during fermentation. Looking back at numerous strategies undertaken over the past four decades to improve recombinant protein production in S. cerevisiae, it is evident that various steps in the protein production "pipeline" can be manipulated depending on the protein of interest and its anticipated application. In this review, we briefly introduce some of the strategies and highlight lessons learned with regards to improved transcription, translation, post-translational modification and protein secretion of heterologous hydrolases. We examine how host strain selection and modification, as well as enzyme compatibility, are crucial determinants for overall success. Finally, we discuss how lessons from heterologous hydrolase expression can inform modern synthetic biology and genome editing tools to provide process-ready yeast strains in future. However, it is clear that the successful expression of any particular enzyme is still unpredictable and requires a trial-and-error approach.

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.

Customized yeast cell factories for biopharmaceuticals: from cell engineering to process scale up

The manufacture of recombinant therapeutics is a fastest-developing section of therapeutic pharmaceuticals and presently plays a significant role in disease management. Yeasts are established eukaryotic host for heterologous protein production and offer distinctive benefits in synthesising pharmaceutical recombinants. Yeasts are proficient of vigorous growth on inexpensive media, easy for gene manipulations, and are capable of adding post translational changes of eukaryotes. Saccharomyces cerevisiae is model yeast that has been applied as a main host for the manufacture of pharmaceuticals and is the major tool box for genetic studies; nevertheless, numerous other yeasts comprising Pichia pastoris, Kluyveromyces lactis, Hansenula polymorpha, and Yarrowia lipolytica have attained huge attention as non-conventional partners intended for the industrial manufacture of heterologous proteins. Here we review the advances in yeast gene manipulation tools and techniques for heterologous pharmaceutical protein synthesis. Application of secretory pathway engineering, glycosylation engineering strategies and fermentation scale-up strategies in customizing yeast cells for the synthesis of therapeutic proteins has been meticulously described.

Recent Developments in Bioprocessing of Recombinant Proteins: Expression Hosts and Process Development

Infectious diseases, along with cancers, are among the main causes of death among humans worldwide. The production of therapeutic proteins for treating diseases at large scale for millions of individuals is one of the essential needs of mankind. Recent progress in the area of recombinant DNA technologies has paved the way to producing recombinant proteins that can be used as therapeutics, vaccines, and diagnostic reagents. Recombinant proteins for these applications are mainly produced using prokaryotic and eukaryotic expression host systems such as mammalian cells, bacteria, yeast, insect cells, and transgenic plants at laboratory scale as well as in large-scale settings. The development of efficient bioprocessing strategies is crucial for industrial production of recombinant proteins of therapeutic and prophylactic importance. Recently, advances have been made in the various areas of bioprocessing and are being utilized to develop effective processes for producing recombinant proteins. These include the use of high-throughput devices for effective bioprocess optimization and of disposable systems, continuous upstream processing, continuous chromatography, integrated continuous bioprocessing, Quality by Design, and process analytical technologies to achieve quality product with higher yield. This review summarizes recent developments in the bioprocessing of recombinant proteins, including in various expression systems, bioprocess development, and the upstream and downstream processing of recombinant proteins.