Bacterial Inclusion Bodies: Discovering Their Better Half

Abstract

Bacterial inclusion bodies are functional, non-toxic amyloids occurring in recombinant bacteria that show analogies with secretory granules of the mammalian endocrine system. The scientific interest in these mesoscale protein aggregates has been historically masked by their status as a hurdle in recombinant protein production.However, insights into their molecular organization and the progressive understanding on how the cell handles the quality of recombinant polypeptides have stimulated the interest on inclusion bodies and opened ways for their usability in diverse technological fields. The engineering and tailoring of inclusion bodies as functional protein particles for materials science and biomedicine is a good example of how formerly undesired bacterial by-products can be re-discovered as promising functional materials for a broad spectrum of applications.-2 - BACKGROUND

Protein based therapeutic delivery agents: Contemporary developments and challenges

“…However, over the past decade, research has revealed that IBs are formed by a mixture of amyloid protein and 70 ~ 95% recombinant proteins with native confirmation, which provide the featured functionality with additional mechanical stability [264, 265]. The Villaverde group has intensively explored the merits of IBs for applications in biotechnology and medicine [265].…”

“…However, over the past decade, research has revealed that IBs are formed by a mixture of amyloid protein and 70 ~ 95% recombinant proteins with native confirmation, which provide the featured functionality with additional mechanical stability [264, 265]. The Villaverde group has intensively explored the merits of IBs for applications in biotechnology and medicine [265]. In a previous study, several IBs formed by critical human proteins including the enzymes dihydrofolate reductase (DHFR) and catalase (CAT), the growth factor leukemia inhibitory factor (LIF), and the chaperon Hsp70 have resulted in positive physiological impact to the mammalian cells, exhibiting significant enhancement of cell survival and/or proliferation under stress conditions and inhibition of apoptosis [247].…”

Wanted: more monitoring and control during inclusion body processing

“…However, due to its reducing environment in the cytoplasm and the metabolic burden posed by recombinant protein production, most products of interest (POI) aggregate to incorrectly folded particles, termed inclusion bodies (IB). They occur in the polar region of the cell and are characterized by a porous structure, hydration, spherical or rod-shaped appearance and a diameter of about 1 µm (Bowden et al 1991; Rinas et al 2017). In the past, many protocols aimed at avoiding IB formation during heterologous protein production.…”

“…Thus, versatile, direct applications for IBs have been developed ever since: immobilized catalysts, scaffolds in tissue engineering, models for amyloidosis and prion propagation, functional materials in tissue engineering, targeted and non-targeted drug delivery systems or implantable depots of therapeutic proteins (Rinas et al 2017). …”

“…Therefore, it is of utmost importance to enhance the yield and lower the production expenses for POIs to enable economic industrial production. Considering this, IB production is an option with several advantages, like high product yield, up to 95% POI purity within the IBs, high mechanical and thermal stability and resistance to proteases (Eggenreich et al 2016; Rinas et al 2017). Currently, a growing number of recombinant products is produced as IBs, which are then processed into soluble product (Table 1).…”