HeLa Based Cell Free Expression Systems for Expression of Plasmodium Rhoptry Proteins

Design, Development and Optimization of a Functional Mammalian Cell-Free Protein Synthesis Platform

In this paper, we describe the stepwise development of a cell-free protein synthesis (CFPS) platform derived from cultured Chinese hamster ovary (CHO) cells. We provide a retrospective summary of the design challenges we faced, and the optimized methods developed for the cultivation of cells and the preparation of translationally active lysates. To overcome low yields, we developed procedures to supplement two accessory proteins, GADD34 and K3L, into the reaction to prevent deactivation of the translational machinery by phosphorylation. We compared different strategies for implementing these accessory proteins including two variants of the GADD34 protein to understand the potential trade-offs between yield and ease of implementation. Addition of the accessory proteins increased yield of turbo Green Fluorescent Protein (tGFP) by up to 100-fold depending on which workflow was used. Using our optimized protocols as a guideline, users can successfully develop their own functional CHO CFPS system, allowing for broader application of mammalian CFPS.

PURE mRNA display and cDNA display provide rapid detection of core epitope motif via high-throughput sequencing

The reconstructed in vitro translation system known as the PURE system has been used in a variety of cell-free experiments such as the expression of native and de novo proteins as well as various display methods to select for functional polypeptides. We developed a refined PURE-based display method for the preparation of stable messenger RNA (mRNA) and complementary DNA (cDNA)-peptide conjugates and validated its utility for in vitro selection. Our conjugate formation efficiency exceeded 40%, followed by gel purification to allow minimum carry-over of components from the translation system to the downstream assay enabling clean and efficient random peptide sequence screening. We chose the commercially available anti-FLAG M2 antibody as a target molecule for validation. Starting from approximately 1.7 × 10¹² random sequences, a round-by-round high-throughput sequencing showed clear enrichment of the FLAG epitope DYKDDD as well as revealing consensus FLAG epitope motif DYK(D/L/N)(L/Y/D/N/F)D. Enrichment of core FLAG motifs lacking one of the four key residues (DYKxxD) indicates that Tyr (Y) and Lys (K) appear as the two key residues essential for binding. Furthermore, the comparison between mRNA display and cDNA display method resulted in overall similar performance with slightly higher enrichment for mRNA display. We also show that gel purification steps in the refined PURE-based display method improve conjugate formation efficiency and enhance the enrichment rate of FLAG epitope motifs in later rounds of selection especially for mRNA display. Overall, the generalized procedure and consistent performance of two different display methods achieved by the commercially available PURE system will be useful for future studies to explore the sequence and functional space of diverse polypeptides.

Cell-Free Protein Synthesis: A Promising Option for Future Drug Development

Proteins are the main source of drug targets and some of them possess therapeutic potential themselves. Among them, membrane proteins constitute approximately 50% of the major drug targets. In the drug discovery pipeline, rapid methods for producing different classes of proteins in a simple manner with high quality are important for structural and functional analysis. Cell-free systems are emerging as an attractive alternative for the production of proteins due to their flexible nature without any cell membrane constraints. In a bioproduction context, open systems based on cell lysates derived from different sources, and with batch-to-batch consistency, have acted as a catalyst for cell-free synthesis of target proteins. Most importantly, proteins can be processed for downstream applications like purification and functional analysis without the necessity of transfection, selection, and expansion of clones. In the last 5 years, there has been an increased availability of new cell-free lysates derived from multiple organisms, and their use for the synthesis of a diverse range of proteins. Despite this progress, major challenges still exist in terms of scalability, cost effectiveness, protein folding, and functionality. In this review, we present an overview of different cell-free systems derived from diverse sources and their application in the production of a wide spectrum of proteins. Further, this article discusses some recent progress in cell-free systems derived from Chinese hamster ovary and Sf21 lysates containing endogenous translocationally active microsomes for the synthesis of membrane proteins. We particularly highlight the usage of internal ribosomal entry site sequences for more efficient protein production, and also the significance of site-specific incorporation of non-canonical amino acids for labeling applications and creation of antibody drug conjugates using cell-free systems. We also discuss strategies to overcome the major challenges involved in commercializing cell-free platforms from a laboratory level for future drug development.

Accelerating the Production of Druggable Targets: Eukaryotic Cell-Free Systems Come into Focus

In the biopharmaceutical pipeline, protein expression systems are of high importance not only for the production of biotherapeutics but also for the discovery of novel drugs. The vast majority of drug targets are proteins, which need to be characterized and validated prior to the screening of potential hit components and molecules. A broad range of protein expression systems is currently available, mostly based on cellular organisms of prokaryotic and eukaryotic origin. Prokaryotic cell-free systems are often the system of choice for drug target protein production due to the simple generation of expression hosts and low cost of preparation. Limitations in the production of complex mammalian proteins appear due to inefficient protein folding and posttranslational modifications. Alternative protein production systems, so-called eukaryotic cell-free protein synthesis systems based on eukaryotic cell-lysates, close the gap between a fast protein generation system and a high quality of complex mammalian proteins. In this study, we show the production of druggable target proteins in eukaryotic cell-free systems. Functional characterization studies demonstrate the bioactivity of the proteins and underline the potential for eukaryotic cell-free systems to significantly improve drug development pipelines.

A User's Guide to Cell-Free Protein Synthesis

Cell-free protein synthesis (CFPS) is a platform technology that provides new opportunities for protein expression, metabolic engineering, therapeutic development, education, and more. The advantages of CFPS over in vivo protein expression include its open system, the elimination of reliance on living cells, and the ability to focus all system energy on production of the protein of interest. Over the last 60 years, the CFPS platform has grown and diversified greatly, and it continues to evolve today. Both new applications and new types of extracts based on a variety of organisms are current areas of development. However, new users interested in CFPS may find it challenging to implement a cell-free platform in their laboratory due to the technical and functional considerations involved in choosing and executing a platform that best suits their needs. Here we hope to reduce this barrier to implementing CFPS by clarifying the similarities and differences amongst cell-free platforms, highlighting the various applications that have been accomplished in each of them, and detailing the main methodological and instrumental requirement for their preparation. Additionally, this review will help to contextualize the landscape of work that has been done using CFPS and showcase the diversity of applications that it enables.

Self-assembling functional programmable protein array for studying protein-protein interactions in malaria parasites

Background

Plasmodium vivax is the most widespread malarial species, causing significant morbidity worldwide. Knowledge is limited regarding the molecular mechanism of invasion due to the lack of a continuous in vitro culture system for these species. Since protein–protein and host–cell interactions play an essential role in the microorganism’s invasion and replication, elucidating protein function during invasion is critical when developing more effective control methods. Nucleic acid programmable protein array (NAPPA) has thus become a suitable technology for studying protein–protein and host–protein interactions since producing proteins through the in vitro transcription/translation (IVTT) method overcomes most of the drawbacks encountered to date, such as heterologous protein production, stability and purification.

Results

Twenty P. vivax proteins on merozoite surface or in secretory organelles were selected and successfully cloned using gateway technology. Most constructs were displayed in the array expressed in situ, using the IVTT method. The Pv12 protein was used as bait for evaluating array functionality and co-expressed with P. vivax cDNA display in the array. It was found that Pv12 interacted with Pv41 (as previously described), as well as PvMSP1_42kDa, PvRBP1a, PvMSP8 and PvRAP1.

Conclusions

NAPPA is a high-performance technique enabling co-expression of bait and query in situ, thereby enabling interactions to be analysed rapidly and reproducibly. It offers a fresh alternative for studying protein–protein and ligand–receptor interactions regarding a parasite which is difficult to cultivate (i.e. P. vivax).

Electronic supplementary material

The online version of this article (10.1186/s12936-018-2414-2) contains supplementary material, which is available to authorized users.

Non-conventional expression systems for the production of vaccine proteins and immunotherapeutic molecules

The increasing demand for recombinant vaccine antigens or immunotherapeutic molecules calls into question the universality of current protein expression systems. Vaccine production can require relatively low amounts of expressed materials, but represents an extremely diverse category consisting of different target antigens with marked structural differences. In contrast, monoclonal antibodies, by definition share key molecular characteristics and require a production system capable of very large outputs, which drives the quest for highly efficient and cost-effective systems. In discussing expression systems, the primary assumption is that a universal production platform for vaccines and immunotherapeutics will unlikely exist. This review provides an overview of the evolution of traditional expression systems, including mammalian cells, yeast and E.coli, but also alternative systems such as other bacteria than E. coli, transgenic animals, insect cells, plants and microalgae, Tetrahymena thermophila, Leishmania tarentolae, filamentous fungi, cell free systems, and the incorporation of non-natural amino acids.