Microbial secretion of biologically active human transforming growth factor alpha fused to the Streptomyces protease inhibitor

Streptomycetes: Attractive Hosts for Recombinant Protein Production

Enzymes are increasingly applied as biocatalysts for fulfilling industrial needs in a variety of applications and there is a bursting of interest for novel therapeutic proteins. Consequently, developing appropriate expression platforms for efficiently producing such recombinant proteins represents a crucial challenge. It is nowadays widely accepted that an ideal ‘universal microbial host’ for heterologous protein expression does not exist. Indeed, the first-choice microbes, as Escherichia coli or yeasts, possess known intrinsic limitations that inevitably restrict their applications. In this scenario, bacteria belonging to the Streptomyces genus need to be considered with more attention as promising, alternative, and versatile platforms for recombinant protein production. This is due to their peculiar features, first-of-all their natural attitude to secrete proteins in the extracellular milieu. Additionally, streptomycetes are considered robust and scalable industrial strains and a wide range of tools for their genetic manipulation is nowadays available. This mini-review includes an overview of recombinant protein production in streptomycetes, covering nearly 100 cases of heterologous proteins expressed in these Gram-positives from the 1980s to December 2019. We investigated homologous sources, heterologous hosts, and molecular tools (promoters/vectors/signal peptides) used for the expression of these recombinant proteins. We reported on their final cellular localization and yield. Thus, this analysis might represent a useful source of information, showing pros and cons of using streptomycetes as platform for recombinant protein production and paving the way for their more extensive use in future as alternative heterologous hosts.

A Review of the Microbial Production of Bioactive Natural Products and Biologics

A variety of organisms, such as bacteria, fungi, and plants, produce secondary metabolites, also known as natural products. Natural products have been a prolific source and an inspiration for numerous medical agents with widely divergent chemical structures and biological activities, including antimicrobial, immunosuppressive, anticancer, and anti-inflammatory activities, many of which have been developed as treatments and have potential therapeutic applications for human diseases. Aside from natural products, the recent development of recombinant DNA technology has sparked the development of a wide array of biopharmaceutical products, such as recombinant proteins, offering significant advances in treating a broad spectrum of medical illnesses and conditions. Herein, we will introduce the structures and diverse biological activities of natural products and recombinant proteins that have been exploited as valuable molecules in medicine, agriculture and insect control. In addition, we will explore past and ongoing efforts along with achievements in the development of robust and promising microorganisms as cell factories to produce biologically active molecules. Furthermore, we will review multi-disciplinary and comprehensive engineering approaches directed at improving yields of microbial production of natural products and proteins and generating novel molecules. Throughout this article, we will suggest ways in which microbial-derived biologically active molecular entities and their analogs could continue to inspire the development of new therapeutic agents in academia and industry.

Secretory production of recombinant proteins by Streptomyces

Bacterial systems are widely applied as production platforms for proteins of biopharmaceutical or therapeutic interest and industrial enzymes. Among these prokaryotic systems, streptomycetes are attractive host cells because several strains of these Gram-positive bacteria have a high innate secretion capacity and extensive knowledge on their fermentation is available. A survey of the literature and our own experience suggests that several proteins are secreted to commercially acceptable levels. However, many heterologous proteins, most often of eukaryotic origin, are currently only poorly secreted by this host, indicating the need for further optimization of Streptomyces as a production host. In this review, the considerable efforts and strategies made in recent years aimed at improving streptomycetes as a host for the production of recombinant proteins will be discussed.

Evaluation of a novel subtilisin inhibitor gene and mutant derivatives for the expression and secretion of mouse tumor necrosis factor alpha by Streptomyces lividans

In order to evaluate the expression and secretion signals of the highly secreted subtilisin inhibitor of Streptomyces venezuelae CBS762.70 (VSI) for the production of heterologous proteins by Streptomyces lividans, mouse tumor necrosis factor alpha (mTNF) was chosen as a model protein. The mTNF cDNA was fused to the vsi signal sequence. The analysis of secretion by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and biological activity measurements revealed an efficient translocation of mTNF. Up to 300 mg of secreted biologically active mTNF per liter could be obtained in shaken-flask cultures. By analyzing the effects of mutations in the N region of the VSI signal peptide on secretion, we found that decreasing the +3 charge of the wild-type protein to +2 resulted in a 3- to 10-fold increase in secretion.