Abstract
The production of recombinant proteins in protein expression systems has become an essential tool in modern biotechnology for the mass production of proteins for pharmaceutical, industrial, agricultural and research purposes. Since the advent of recombinant DNA technology, major progress has been made in the evolution and optimization of various expression systems such as bacterial, yeast, insect, mammalian, plant-based and cell-free systems. The selection of an appropriate host is essential for the successful production of proteins, with each expression system having its own set of advantages, including but not limited to: protein yield, production cost, scalability and post-translational modifications. Escherichia coli is the most popular host and is the most widely used system for the production of simpler therapeutic proteins; while mammalian cell lines are used for the production of more complex therapeutic proteins that require more human-like post-translational modifications. With the recent development of genetic engineering, synthetic biology, metabolic pathway optimization and genome editing technologies, expression efficiency, product quality and process scalability have significantly improved. Nevertheless, there are several issues that still remain in the way of recombinant protein production such as protein misfolding and aggregation, degradation by proteases, low recombinant protein expression, and challenges of native post-translational modifications. Additionally, the growing trend towards biologics and personalized medicines requires the creation of more efficient, flexible and cost-effective manufacturing platforms. These will be expected to increase the yield of protein and product consistency, and cut manufacturing costs. Major recombinant protein expression systems are summarized in this review, with a focus on their current status, advantages, disadvantages and industrial applications. It also covers important problems encountered in protein expression, and explores trends that could impact the future of recombinant protein production technologies. Ongoing developments in this area will be vital to the global progress of biotechnology, health care and sustainable industrial development.