The Production of Human β-Glucocerebrosidase in Nicotiana benthamiana Root Culture

Optimising expression and extraction of recombinant proteins in plants

Recombinant proteins are of paramount importance for research, industrial and medical use. Numerous expression chassis are available for recombinant protein production, and while bacterial and mammalian cell cultures are the most widely used, recent developments have positioned transgenic plant chassis as viable and often preferential options. Plant chassis are easily maintained at low cost, are hugely scalable, and capable of producing large quantities of protein bearing complex post-translational modification. Several protein targets, including antibodies and vaccines against human disease, have been successfully produced in plants, highlighting the significant potential of plant chassis. The aim of this review is to act as a guide to producing recombinant protein in plants, discussing recent progress in the field and summarising the factors that must be considered when utilising plants as recombinant protein expression systems, with a focus on optimising recombinant protein expression at the genetic level, and the subsequent extraction and purification of target proteins, which can lead to substantial improvements in protein stability, yield and purity.

Production of recombinant β-glucocerebrosidase in wild-type and glycoengineered transgenic Nicotiana benthamiana root cultures with different N-glycan profiles

Gaucher disease is an inherited lysosomal storage disorder caused by an insufficiency of active β-glucocerebrosidase (GCase). Exogenous recombinant GCase via enzyme replacement therapy is considered the most practical treatment for Gaucher disease. Mannose receptors mediate the efficient uptake of exogenous GCase into macrophages. Thus, terminal mannose residues on N-glycans are essential for the delivery of exogenous GCase. In this study, recombinant GCase was produced in root cultures of wild-type (WT) and glycoengineered transgenic Nicotiana benthamiana with downregulated N-acetylglucosaminyltransferase I expression. Root cultures of WT and glycoengineered transgenic N. benthamiana plants were successfully generated by the induction of plant hormones. Recombinant GCases produced in both root cultures possessed GCase enzyme activity. Purified GCases derived from both root cultures revealed different N-glycan profiles. The WT-derived GCase possessed the predominant plant-type N-glycans, which contain plant-specific sugars-linkages, specifically β1,2-xylose and α1,3-fucose residues. Notably, the mannosidic-type N-glycans with terminal mannose residues were abundant in the purified GCase derived from glycoengineered N. benthamiana root culture. This research provides a promising plant-based system for the production of recombinant GCase with terminal mannose residues on N-glycans.

Transient Production of Human β-Glucocerebrosidase With Mannosidic-Type N-Glycan Structure in Glycoengineered Nicotiana benthamiana Plants

Gaucher disease is an inherited lysosomal storage disorder caused by a deficiency of functional enzyme β-glucocerebrosidase (GCase). Recombinant GCase has been used in enzyme replacement therapy to treat Gaucher disease. Importantly, the terminal mannose N-glycan structure is essential for the uptake of recombinant GCase into macrophages via the mannose receptor. In this research, recombinant GCase was produced using Agrobacterium-mediated transient expression in both wild-type (WT) and N-acetylglucosaminyltransferase I (GnTI) downregulated Nicotiana benthamiana (ΔgntI) plants, the latter of which accumulates mannosidic-type N-glycan structures. The successfully produced functional GCase exhibited GCase enzyme activity. The enzyme activity was the same as that of the conventional mammalian-derived GCase. Notably, N-glycan analysis revealed that a mannosidic-type N-glycan structure lacking plant-specific N-glycans (β1,2-xylose and α1,3-fucose residues) was predominant in all glycosylation sites of purified GCase produced from ΔgntI plants. Our research provides a promising alternative plant line as a host for the production of recombinant GCase with a mannosidic-type N-glycan structure. This glycoengineered plant might be applicable to the production of other pharmaceutical proteins, especially mannose receptor targeted protein, for therapeutic uses.

Enzyme kinetics and inhibition parameters of human leukocyte glucosylceramidase

Glucosylceramidase (GCase) is a lysosomal enzyme that catalyzes the cleavage of β-glucosidic linkage of glucocerebroside (GC) into glucose and ceramide; thereby, plays an essential function in the degradation of complex lipids and the turnover of cellular membranes. The growing list of 460 mutations in the gene coding for it-glucosylceramidase beta acid 1 (GBA1)-is reported to abolish its catalytic activity and decrease its enzyme stability, associating it with severe health conditions such as Gaucher disease (GD), Parkinson Disease (PD) and Dementia with Lewy bodies (DLB). Although the three-dimensional structure of wild type glucosylceramidase is elucidated, little is known about its features in human cells. Moreover, alternative sources of GCase that prove to be effective in the treatment of diseases with enzyme treatment therapies, impose the need for a simple and cost-effective procedure to study the enzyme behavior. This work, for the first time, shows a well-established, yet simple, cost- and time-efficient protocol for the study of GCase enzyme in human leukocytes by the artificial substrate p-Nitrophenyl-β-D-glucopyranoside (PNPG). Characterization of the enzyme in human leukocytes for activation parameters (optimal pH, Km, and Vmax) and enzyme inhibition was done. The results indicate that the optimum pH of GCase enzyme with PNPG is 5.0. The Km and Vmax values are 12.6mM and 333 U/mg, respectively. Gluconolactone competitively inhibits GCase, with a Ki value of 0.023 mM and IC50 of 0.047 mM. Glucose inhibition is uncompetitive with a Ki of 1.94 mM and IC50 of 55.3 mM. This is the first report for the inhibitory effect of glucose, δ-gluconolactone on human leukocyte GCase activity.

Plant Glycosides and Glycosidases: A Treasure-Trove for Therapeutics

Plants contain numerous glycoconjugates that are metabolized by specific glucosyltransferases and hydrolyzed by specific glycosidases, some also catalyzing synthetic transglycosylation reactions. The documented value of plant-derived glycoconjugates to beneficially modulate metabolism is first addressed. Next, focus is given to glycosidases, the central theme of the review. The therapeutic value of plant glycosidases is discussed as well as the present production in plant platforms of therapeutic human glycosidases used in enzyme replacement therapies. The increasing knowledge on glycosidases, including structure and catalytic mechanism, is described. The novel insights have allowed the design of functionalized highly specific suicide inhibitors of glycosidases. These so-called activity-based probes allow unprecedented visualization of glycosidases cross-species. Here, special attention is paid on the use of such probes in plant science that promote the discovery of novel enzymes and the identification of potential therapeutic inhibitors and chaperones.

Production of recombinant human acid β-glucosidase with high mannose-type N-glycans in rice gnt1 mutant for potential treatment of Gaucher disease

Gaucher disease is an inherited metabolic disease caused by genetic acid β -glucosidase (GBA) deficiency and is currently treated by enzyme replacement therapy. For uptake into macrophages, GBA needs to carry terminal mannose residues on their N-glycans. Knockout mutant rice of N-acetylglucosaminyltransferase-I (gnt1) have a disrupted N-glycan processing pathway and produce only glycoproteins with high mannose residues. In this study, we introduced a gene encoding recombinant human GBA into both wild-type rice (WT) and rice gnt1 calli. Target gene integration and mRNA expression were confirmed by genomic DNA PCR and Northern blotting, respectively. Secreted rhGBAs in culture media from cell lines originating from both WT (WT-GBA) and rice gnt1 (gnt1-GBA) were detected by Western blotting. Each rhGBA was purified by affinity and ion exchange chromatography. In vitro catalytic activity of purified rhGBA was comparable to commercial Chinese hamster ovary cell-derived rhGBA. N-glycans were isolated from WT-GBA and gnt1-GBA and analyzed by using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry. The amounts of high mannose-type N-glycans were highly elevated in gnt1-GBA (100%) compared to WT-GBA (1%).

Bioproduction of a Therapeutic Vaccine Against Human Papillomavirus in Tomato Hairy Root Cultures

Human papillomavirus (HPV) tumor disease is a critical public health problem worldwide, especially in the developing countries. The recognized pathogenic function of E5, E6, and E7 oncoproteins offers the opportunity to devise therapeutic vaccines based on engineered recombinant proteins. The potential of plants to manufacture engineered compounds for pharmaceutical purposes, from small to complex protein molecules, allows the expression of HPV antigens and, possibly, the regulation of immune functions to develop very specific therapies as a reinforcement to available nonspecific therapies and preventive vaccination also in developed countries. Among plant-based expression formats, hairy root cultures are a robust platform combining the benefits of eukaryotic plant-based bioreactors, with those typical of cell cultures. In this work, to devise an experimental therapeutic vaccine against HPV, hairy root cultures were used to express a harmless form of the HPV type 16 E7 protein (E7*) fused to SAPKQ, a noncytotoxic form of the saporin protein from Saponaria officinalis, that we had shown to improve E7-specific cell-mediated responses as a fusion E7*-SAPKQ DNA vaccine. Hairy root clones expressing the E7*-SAPKQ candidate vaccine were obtained upon infection of leaf explants of Solanum lycopersicum using a recombinant plant expression vector. Yield was approximately 35.5 μg/g of fresh weight. Mouse immunization with vaccine-containing crude extracts was performed together with immunological and biological tests to investigate immune responses and anticancer activity, respectively. Animals were primed with either E7*-SAPKQ DNA-based vaccine or E7*-SAPKQ root extract-based vaccine and boosted with the same (homologous schedule) or with the other vaccine preparation (heterologous schedule) in the context of TC-1 experimental mouse model of HPV-associated tumor. All the formulations exhibited an immunological response associated to anticancer activity. In particular, DNA as prime and hairy root extract as boost demonstrated the highest efficacy. This work, based on the development of low-cost technologies, highlights the suitability of hairy root cultures as possible biofactories of therapeutic HPV vaccines and underlines the importance of the synergic combination of treatment modalities for future developments in this field.