Purification and site-specific N-glycosylation analysis of human recombinant butyrylcholinesterase from Nicotiana benthamiana

Comparative analysis of the Squamosa Promoter Binding-Like (SPL) gene family in Nicotiana benthamiana and Nicotiana tabacum

SQUAMOSA PROMOTER BINDING-LIKE (SPL) proteins constitute a large family of transcription factors known to play key roles in growth and developmental processes, including juvenile-to-adult and vegetative-to-reproductive phase transitions. This makes SPLs interesting targets for precision breeding in plants of the Nicotiana genus used as e.g. recombinant biofactories. We report the identification of 49 SPL genes in Nicotiana tabacum cv. K326 and 43 SPL genes in Nicotiana benthamiana LAB strain, which were classified into eight phylogenetic groups according to the SPL classification in Arabidopsis. Exon-intron gene structure and DNA-binding domains were highly conserved between homeologues and orthologues. Thirty of the NbSPL genes and 33 of the NtSPL genes were found to be possible targets of microRNA 156. The expression of SPL genes in leaves was analysed by RNA-seq at three different stages, revealing that genes not under miR156 control were in general constitutively expressed at high levels, whereas miR156-regulated genes showed lower expression, often developmentally regulated. We selected the N. benthamiana SPL13_1a gene as target for a CRISPR/Cas9 knock-out experiment. We show here that a full knock-out in this single gene leads to a significant delay in flowering time, a trait that could be exploited to increase biomass for recombinant protein production.

Analysis of Variability of Functionals of Recombinant Protein Production Trajectories Based on Limited Data

Making statistical inference on quantities defining various characteristics of a temporally measured biochemical process and analyzing its variability across different experimental conditions is a core challenge in various branches of science. This problem is particularly difficult when the amount of data that can be collected is limited in terms of both the number of replicates and the number of time points per process trajectory. We propose a method for analyzing the variability of smooth functionals of the growth or production trajectories associated with such processes across different experimental conditions. Our modeling approach is based on a spline representation of the mean trajectories. We also develop a bootstrap-based inference procedure for the parameters while accounting for possible multiple comparisons. This methodology is applied to study two types of quantities—the “time to harvest” and “maximal productivity”—in the context of an experiment on the production of recombinant proteins. We complement the findings with extensive numerical experiments comparing the effectiveness of different types of bootstrap procedures for various tests of hypotheses. These numerical experiments convincingly demonstrate that the proposed method yields reliable inference on complex characteristics of the processes even in a data-limited environment where more traditional methods for statistical inference are typically not reliable.

Immobilization of transgenic plant cells towards bioprinting for production of a recombinant biodefense agent

Transgenic rice cells (Oryza sativa) producing recombinant butyrylcholinesterase (BChE) as a prophylactic/therapeutic against organophosphate nerve agent poisoning, cocaine toxicity, and neurodegenerative diseases like Alzheimer's were immobilized in a polyethylene glycol-based hydrogel. The cells were sustained for 14 days in the semi-solid matrix, undergoing a growth phase from days 0-6, a BChE production phase in sugar-free medium from days 6-12, and a growth/recovery phase from days 12-14. Throughout this period, the cells maintained similar viability to those in suspension cultures and displayed analogous sugar consumption trends. The rice cells in the hydrogel also produced a significant amount of active BChE, comparable to the levels produced in liquid cultures. A considerable fraction of this BChE was secreted into the media, allowing for easier product separation. To the best of our knowledge, this proof-of-concept is the first report of immobilization of recombinant plant cells for continuous production of high-value heterologous proteins. This work serves as a foundation for further investigation towards plant cell bioprinting and the development of a simple, efficient, robust, modular, and potentially field-deployable bioreactor system for the manufacture of biologics. GRAPHICAL ABSTRACT AND LAY SUMMARY: Transgenic rice cells were combined with a polyethylene glycol tetra-acrylate (PEGTA) and lithium phenyl-2,4,6-trimethylbenzoylphosphinate (LAP) bioink and cured with UV light to construct an immobilized cell-based protein production system. The cells were maintained for 14 days in the hydrogel matrix and were induced to actively make and secrete recombinant butyrylcholinesterase, a complex enzyme that irreversibly binds to and can hydrolyze organophosphate. This proof-of-concept study showcases the use of immobilized and potentially bioprintable plant cells to produce high-value proteins with prophylactic and therapeutic applications.

Production of recombinant butyrylcholinesterase from transgenic rice cell suspension cultures in a pilot-scale bioreactor

Producing recombinant proteins in transgenic plant cell suspension cultures in bioreactors provides controllability, reproducibility, scalability, and low-cost production, although low yields remain the major challenge. The studies on scaling-up to pilot-scale bioreactors, especially in conventional stainless-steel stirred tank bioreactors (STB), to produce recombinant proteins in plant cell suspension cultures are very limited. In this study, we scaled-up the production of rice recombinant butyrylcholinesterase (rrBChE), a complex hydrolase enzyme that can be used to prophylactically and therapeutically treat against organophosphorus nerve agents and pesticide exposure, from metabolically regulated transgenic rice cell suspension cultures in a 40-L pilot-scale STB. Employing cyclical operation together with a simplified-process operation (controlling gas sparging rate rather than dissolved oxygen and allowing natural sugar depletion) identified in lab-scale (5 L) bioreactor studies, we found a consistent maximum total active rrBChE production level of 46-58 µg/g fresh weight in four cycles over 82 days of semicontinuous operation. Additionally, maintaining the overall volumetric oxygen mass transfer coefficient (k_L a) in the pilot-scale STB to be equivalent to the lab-scale STB improves the maximum total active rrBChE production level and the maximum volumetric productivity to 85 µg/g fresh weight and 387 µg L^-1  day^-1 , respectively, which are comparable to the lab-scale culture. Here, we demonstrate pilot-scale bioreactor performance using a metabolically regulated transgenic rice cell culture for long-term, reproducible, and sustained production of rrBChE.

Effects of Kifunensine on Production and N-Glycosylation Modification of Butyrylcholinesterase in a Transgenic Rice Cell Culture Bioreactor

The production and N-glycosylation of recombinant human butyrylcholinesterase (BChE), a model highly glycosylated therapeutic protein, in a transgenic rice cell suspension culture treated with kifunensine, a strong α-mannosidase I inhibitor, was studied in a 5 L bioreactor. A media exchange was performed at day 7 of cultivation by removing spent sugar-rich medium (NB+S) and adding fresh sugar-free (NB-S) medium to induce the rice α-amylase 3D (RAmy3D) promoter to produce rice recombinant human BChE (rrBChE). Using a 1.25X-concentrated sugar-free medium together with an 80% reduced working volume during the media exchange led to a total active rrBChE production level of 79 ± 2 µg (g FW)^-1 or 7.5 ± 0.4 mg L^-1 in the presence of kifunensine, which was 1.5-times higher than our previous bioreactor runs using normal sugar-free (NB-S) media with no kifunensine treatment. Importantly, the amount of secreted active rrBChE in culture medium was enhanced in the presence of kifunensine, comprising 44% of the total active rrBChE at day 5 following induction. Coomassie-stained SDS-PAGE gel and Western blot analyses revealed different electrophoretic migration of purified rrBChE bands with and without kifunensine treatment, which was attributed to different N-glycoforms. N-Glycosylation analysis showed substantially increased oligomannose glycans (Man5/6/7/8) in rrBChE treated with kifunensine compared to controls. However, the mass-transfer limitation of kifunensine was likely the major reason for incomplete inhibition of α-mannosidase I in this bioreactor study.

Expression optimization, purification and in vitro characterization of human epidermal growth factor produced in Nicotiana benthamiana

Human epidermal growth factor (hEGF) has gained clinical importance due to its ability to promote wound healing. Due to its commercial applications and high market demand, recombinant EGF has been produced in several forms. Currently, plant expression system is considered as potential alternative for low-cost recombinant protein production. Hence, this study focused on improving the production of hEGF in plants by effective gene construct design and optimizing the Agrobacterium culture conditions for high protein production. In this context, hEGF gene was cloned into plant geminiviral expression vector pBYR2e and transformed in to N. benthamiana leaves via., agroinfiltration. The recombinant hEGF was purified from the plant crude extracts by single-step affinity chromatography. Furthermore, the plant-produced hEGF has shown to promote cell migration comparable to commercial hEGF in HaCaT cells in vitro. These results indicated the potential of plant expression system for the production of recombinant hEGF for tissue engineering applications.