ExploitingLeishmania tarentolaecell-free extracts for the synthesis of human solute carriers

Advanced applications of Nanodiscs-based platforms for antibodies discovery

Due to their fundamental biological importance, membrane proteins (MPs) are attractive targets for drug discovery, with cell surface receptors, transporters, ion channels, and membrane-bound enzymes being of particular interest. However, due to numerous challenges, these proteins present underutilized opportunities for discovering biotherapeutics. Antibodies hold the promise of exquisite specificity and adaptability, making them the ideal candidates for targeting complex membrane proteins. They can target specific conformations of a particular membrane protein and can be engineered into various formats. Generating specific and effective antibodies targeting these proteins is no easy task due to several factors. The antigen's design, antibody-generation strategies, lead optimization technologies, and antibody modalities can be modified to tackle these challenges. The rational employment of cutting-edge lipid nanoparticle systems for retrieving the membrane antigen has been successfully implemented to simplify the mechanism-based therapeutic antibody discovery approach. Despite the highlighted MP production challenges, this review unequivocally underscores the advantages of targeting complex membrane proteins with antibodies and designing membrane protein antigens. Selected examples of lipid nanoparticle success have been illustrated, emphasizing the potential of therapeutic antibody discovery in this regard. With further research and development, we can overcome these challenges and unlock the full potential of therapeutic antibodies directed to target complex MPs.

Development of Lyophilized Eukaryotic Cell-Free Protein Expression System Based on Leishmania tarentolae

Eukaryotic cell-free protein expression systems enable rapid production of recombinant multidomain proteins in their functional form. A cell-free system based on the rapidly growing protozoan Leishmania tarentolae (LTE) has been extensively used for protein engineering and analysis of protein interaction networks. However, like other eukaryotic cell-free systems, LTE deteriorates at ambient temperatures and requires deep freezing for transport and storage. In this study, we report the development of a lyophilized version of LTE. Use of lyoprotectants such as poly(ethylene glycol) and trehalose during the drying process allows retention of 76% of protein expression activity versus nonlyophilized controls. Lyophilized LTE is capable of withstanding storage at room temperature for over 2 weeks. We demonstrated that upon reconstitution the lyophilized LTE could be used for in vitro expression of active enzymes, analysis of protein-protein interactions by AlphaLISA assay, and functional analysis of protein biosensors. Development of lyophilized LTE lowers the barriers to its distribution and opens the door to its application in remote areas.

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.

Heterologous expression of the mammalian sodium-nucleobase transporter rSNBT1 in Leishmania tarentolae

Recombinant expression systems for mammalian membrane transport proteins are often limited by insufficient yields to support structural studies, inadequate post-translational processing and problems related with improper membrane targeting or cytotoxicity. Use of alternative expression systems and optimization of expression/purification protocols are constantly needed. In this work, we explore the applicability of the laboratory strain LEXSY of the ancient eukaryotic microorganism Leishmania tarentolae as a new expression system for mammalian nucleobase permeases of the NAT/NCS2 (Nucleobase-Ascorbate Transporter/Nucleobase-Cation Symporter-2) family. We achieved the heterologous expression of the purine-pyrimidine permease rSNBT1 from Rattus norvegicus (tagged at C-terminus with a red fluorescent protein), as confirmed by confocal microscopy and biochemical analysis of the subcellular fractions enriched in membrane proteins. The cDNA of rSNBT1 has been subcloned in a pLEXSY-sat-mrfp1vector and used to generate transgenic L. tarentolae-rsnbt1-mrfp1 strains carrying the pLEXSY-sat-rsnbt1-mrfp1 plasmid either episomally or integrated in the chromosomal DNA. The chimeric transporter rSNBT1-mRFP1 is targeted to the ER and the plasma membrane of the L. tarentolae promastigotes. The transgenic strains are capable of transporting nucleobases that are substrates of rSNBT1 but also of the endogenous L. tarentolae nucleoside/nucleobase transporters. A dipyridamole-resistant Na⁺-dependent fraction of uptake is attributed to the exogenously expressed rSNBT1.

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.

Unexpected instabilities explain batch-to-batch variability in cell-free protein expression systems

Cell-free methods of protein synthesis offer rapid access to expressed proteins. Though the amounts produced are generally only at a small scale, these are sufficient to perform protein-protein interaction assays and tests of enzymatic activity. As such they are valuable tools for the biochemistry and bioengineering community. However the most complex, eukaryotic cell-free systems are difficult to manufacture in house and can be prohibitively expensive to obtain from commercial sources. The Leishmania tarentolae system offers a relatively cheap alternative which is capable of producing difficult to express proteins, but which is simpler to produce in large scale. However, this system suffers from batch-to-batch variability, which has been accepted as a consequence of the complexity of the extracts. Here we show an unexpected origin for the variability observed and demonstrate that small variations in a single parameter can dramatically affect expression, such that minor pipetting errors can have major effects on yields. L. tarentolae cell-free lysate activity is shown to be more stable to changes in Mg²⁺ concentration at a lower ratio of feed solution to lysate in the reaction than typically used, and a higher Mg²⁺ optimum. These changes essentially eliminate batch-to-batch variability of L. tarentolae lysate activity and permit their full potential to be realized.

Leishmania tarentolae as a host for heterologous expression of functional human ABCB6 transporter

The need for large amounts of reproducibly produced and isolated protein arises not only in structural studies, but even more so in biochemical ones, and with regard to ABC transporters it is especially pressing when faced with the prospect of enzymatic/transport activity studies, substrate screening etc. Thus, reliable heterologous expression systems/model organisms for large and complex proteins are at a premium. We have verified the applicability of the recently established novel eukaryotic expression system, using Leishmania tarentolae as a host, for human ABC protein overexpression. We succeeded in overexpressing human ABCB6, a protein with controversial subcellular localization and multiple proposed cellular functions. We were able to demonstrate its efficient expression in the expected subcellular locations as well as biochemical activity of the overexpressed protein (ATPase activity and porphyrin-like substrate transport). This activity was absent in cells overexpressing the catalytically inactive variant of ABCB6 (K629M). We demonstrate the possibility of applying a cost-effective expression system to study the activity of membrane transporters from the ABC superfamily.