Protein bodies: how the ER deals with high accumulation of recombinant proteins
Citation
Saberianfar, R. and Menassa, R. (2017) Protein bodies: how the ER deals with high accumulation of recombinant proteins. Plant Biotechnol J 15, 671-673.
Plain language summary
Protein bodies (PBs) are highly specialized protein storage organelles in cereal seeds. PB formation in seeds initiates in the endoplasmic reticulum (ER), and depending on the plant species, PBs remain in the ER or end up in protein storage vacuoles. Protein bodies have also been shown to occur in leaves producing high amounts of foreign proteins. In this commentary we provide a model for how we believe protein bodies are produced in leaf cells, through budding from the Endoplasmic Reticulum (ER) membrane, and continued attachment to the ER membrane system. We argue that PBs in leaves enable the storage of high amounts of recombinant proteins without imposing excessive stress to the cell, and may be a coping mechanism that eukaryotic cells have evolved to prevent stress and cell death. Taking advantage of this phenomenon can constitute an approach to addressing the production bottleneck of low recombinant protein accumulation levels in plants, especially in leaf-based expression systems.
Abstract
© The Author(s). 2017. Background: Alpha amylase hydrolyzes α-bonds of polysaccharides such as starch and produces maltooligosaccharides. Its starch saccharification applications make it an essential enzyme in the textile, food and brewing industries. Commercially available α-amylase is mostly produced from Bacillus or Aspergillus. A hyper-thermostable and Ca 2++ independent α-amylase from Pyrococcus furiosus (PFA) expressed in E.coli forms insoluble inclusion bodies and thus is not feasible for industrial applications. Results: We expressed PFA in Nicotiana tabacum and found that plant-produced PFA forms functional aggregates with an accumulation level up to 3.4 g/kg FW (fresh weight) in field conditions. The aggregates are functional without requiring refolding and therefore have potential to be applied as homogenized plant tissue without extraction or purification. PFA can also be extracted from plant tissue upon dissolution in a mild reducing buffer containing SDS. Like the enzyme produced in P. furiosus and in E. coli, plant produced PFA preserves hyper-thermophilicity and hyper-thermostability and has a long shelf life when stored in lyophilized leaf tissue. With tobacco's large biomass and high yield, hyper-thermostable α-amylase was produced at a scale of 42 kg per hectare. Conclusions: Tobacco may be a suitable bioreactor for industrial production of active hyperthermostable alpha amylase.