@article{chu_prodromou_day_schneible_bacon_bowen_kilgore_catella_moore_mabe_et al._2021, title={Peptides and pseudopeptide ligands: a powerful toolbox for the affinity purification of current and next-generation biotherapeutics}, volume={1635}, ISSN={["1873-3778"]}, DOI={10.1016/j.chroma.2020.461632}, abstractNote={Following the consolidation of therapeutic proteins in the fight against cancer, autoimmune, and neurodegenerative diseases, recent advancements in biochemistry and biotechnology have introduced a host of next-generation biotherapeutics, such as CRISPR-Cas nucleases, stem and car-T cells, and viral vectors for gene therapy. With these drugs entering the clinical pipeline, a new challenge lies ahead: how to manufacture large quantities of high-purity biotherapeutics that meet the growing demand by clinics and biotech companies worldwide. The protein ligands employed by the industry are inadequate to confront this challenge: while featuring high binding affinity and selectivity, these ligands require laborious engineering and expensive manufacturing, are prone to biochemical degradation, and pose safety concerns related to their bacterial origin. Peptides and pseudopeptides make excellent candidates to form a new cohort of ligands for the purification of next-generation biotherapeutics. Peptide-based ligands feature excellent target biorecognition, low or no toxicity and immunogenicity, and can be manufactured affordably at large scale. This work presents a comprehensive and systematic review of the literature on peptide-based ligands and their use in the affinity purification of established and upcoming biological drugs. A comparative analysis is first presented on peptide engineering principles, the development of ligands targeting different biomolecular targets, and the promises and challenges connected to the industrial implementation of peptide ligands. The reviewed literature is organized in (i) conventional (α-)peptides targeting antibodies and other therapeutic proteins, gene therapy products, and therapeutic cells; (ii) cyclic peptides and pseudo-peptides for protein purification and capture of viral and bacterial pathogens; and (iii) the forefront of peptide mimetics, such as β-/γ-peptides, peptoids, foldamers, and stimuli-responsive peptides for advanced processing of biologics.}, journal={JOURNAL OF CHROMATOGRAPHY A}, author={Chu, Wenning and Prodromou, Raphael and Day, Kevin N. and Schneible, John D. and Bacon, Kaitlyn B. and Bowen, John D. and Kilgore, Ryan E. and Catella, Carly M. and Moore, Brandyn D. and Mabe, Matthew D. and et al.}, year={2021}, month={Jan} }
 @article{bacon_blain_bowen_burroughs_mcarthur_menegatti_rao_2021, title={Quantitative Yeast-Yeast Two Hybrid for the Discovery and Binding Affinity Estimation of Protein-Protein Interactions}, volume={10}, ISSN={["2161-5063"]}, DOI={10.1021/acssynbio.0c00472}, abstractNote={Quantifying the binding affinity of protein-protein interactions is important for elucidating connections within biochemical signaling pathways, as well as characterization of binding proteins isolated from combinatorial libraries. We describe a quantitative yeast-yeast two-hybrid (qYY2H) system that not only enables the discovery of specific protein-protein interactions but also efficient, quantitative estimation of their binding affinities (KD). In qYY2H, the bait and prey proteins are expressed as yeast cell surface fusions using yeast surface display. We developed a semiempirical framework for estimating the KD of monovalent bait-prey interactions, using measurements of bait-prey yeast-yeast binding, which is mediated by multivalent interactions between yeast-displayed bait and prey. Using qYY2H, we identified interaction partners of SMAD3 and the tandem WW domains of YAP from a cDNA library and characterized their binding affinities. Finally, we showed that qYY2H could also quantitatively evaluate binding interactions mediated by post-translational modifications on the bait protein.}, number={3}, journal={ACS SYNTHETIC BIOLOGY}, author={Bacon, Kaitlyn and Blain, Abigail and Bowen, John and Burroughs, Matthew and McArthur, Nikki and Menegatti, Stefano and Rao, Balaji M.}, year={2021}, month={Mar}, pages={505–514} }
 @article{bowen_schneible_bacon_labar_menegatti_rao_2021, title={Screening of Yeast Display Libraries of Enzymatically Treated Peptides to Discover Macrocyclic Peptide Ligands}, volume={22}, ISSN={["1422-0067"]}, url={https://www.mdpi.com/1422-0067/22/4/1634}, DOI={10.3390/ijms22041634}, abstractNote={We present the construction and screening of yeast display libraries of post-translationally modified peptides wherein site-selective enzymatic treatment of linear peptides is achieved using bacterial transglutaminase. To this end, we developed two alternative routes, namely (i) yeast display of linear peptides followed by treatment with recombinant transglutaminase in solution; or (ii) intracellular co-expression of linear peptides and transglutaminase to achieve peptide modification in the endoplasmic reticulum prior to yeast surface display. The efficiency of peptide modification was evaluated via orthogonal detection of epitope tags integrated in the yeast-displayed peptides by flow cytometry, and via comparative cleavage of putative cyclic vs. linear peptides by tobacco etch virus (TEV) protease. Subsequently, yeast display libraries of transglutaminase-treated peptides were screened to isolate binders to the N-terminal region of the Yes-Associated Protein (YAP) and its WW domains using magnetic selection and fluorescence activated cell sorting (FACS). The identified peptide cyclo[E-LYLAYPAH-K] featured a KD of 1.75 μM for YAP and 0.68 μM for the WW domains of YAP as well as high binding selectivity against albumin and lysozyme. These results demonstrate the usefulness of enzyme-mediated cyclization in screening combinatorial libraries to identify cyclic peptide binders.}, number={4}, journal={INTERNATIONAL JOURNAL OF MOLECULAR SCIENCES}, author={Bowen, John and Schneible, John and Bacon, Kaitlyn and Labar, Collin and Menegatti, Stefano and Rao, Balaji M.}, year={2021}, month={Feb} }
 @article{bacon_blain_burroughs_mcarthrur_rao_menegatti_2020, title={Isolation of Chemically Cyclized Peptide Binders Using Yeast Surface Display}, volume={22}, ISSN={["2156-8944"]}, DOI={10.1021/acscombsci.0c00076}, abstractNote={Cyclic peptides with engineered protein-binding activity have gained increasing attention for use in therapeutic and biotechnology applications. We describe the efficient isolation and characterization of cyclic peptide binders from genetically encoded combinatorial libraries using yeast surface display. Here, peptide cyclization is achieved by disuccinimidyl glutarate-mediated crosslinking of amine groups with-in a linear peptide sequence that is expressed as a yeast cell surface fusion. Using this approach, we first screened a library of cyclic heptapeptides by magnetic selection and fluorescence activated cell sorting (FACS), to isolate binders for a model target (lysozyme) with low micromolar binding affinity (KD ~ 1.2 - 3.7 M). The isolated peptides bound lysozyme selectively, and only when cyclized. Importantly, we showed that yeast surface displayed cyclic peptides could be used to efficiently obtain quantitative es-timates of binding affinity, without chemical synthesis of the selected peptides. Subsequently, to demonstrate broader applicability of our approach, we isolated cyclic heptapeptides that bind human in-terleukin-17 (IL-17) using yeast-displayed IL-17 as a target for magnetic selection, followed by FACS using recombinant IL-17. Molecular docking simulations and follow-up experimental analyses identi-fied a candidate cyclic peptide that binds IL-17 in its receptor binding region with moderate affinity (KD ~ 300 nM). Taken together, our results show that yeast surface display can be used to efficiently isolate and characterize cyclic peptides generated by chemical modification from combinatorial libraries.}, number={10}, journal={ACS COMBINATORIAL SCIENCE}, author={Bacon, Kaitlyn and Blain, Abigail and Burroughs, Matthew and McArthrur, Nikki and Rao, Balaji M. and Menegatti, Stefano}, year={2020}, month={Oct}, pages={519–532} }
 @misc{bacon_lavoie_rao_daniele_menegatti_2020, title={Past, Present, and Future of Affinity-based Cell Separation Technologies}, volume={112}, ISSN={["1878-7568"]}, DOI={10.1016/j.actbio.2020.05.004}, abstractNote={Progress in cell purification technology is critical to increase the availability of viable cells for therapeutic, diagnostic, and research applications. A variety of techniques are now available for cell separation, ranging from non-affinity methods such as density gradient centrifugation, dielectrophoresis, and filtration, to affinity methods such as chromatography, two-phase partitioning, and magnetic-/fluorescence-assisted cell sorting. For clinical and analytical procedures that require highly purified cells, the choice of cell purification method is crucial, since every method offers a different balance between yield, purity, and bioactivity of the cell product. For most applications, the requisite purity is only achievable through affinity methods, owing to the high target specificity that they grant. In this review, we discuss past and current methods for developing cell-targeting affinity ligands and their application in cell purification, along with the benefits and challenges associated with different purification formats. We further present new technologies, like stimuli-responsive ligands and parallelized microfluidic devices, towards improving the viability and throughput of cell products for tissue engineering and regenerative medicine. Our comparative analysis provides guidance in the multifarious landscape of cell separation techniques and highlights new technologies that are poised to play a key role in the future of cell purification in clinical settings and the biotech industry. STATEMENT OF SIGNIFICANCE: Technologies for cell purification have served science, medicine, and industrial biotechnology and biomanufacturing for decades. This review presents a comprehensive survey of this field by highlighting the scope and relevance of all known methods for cell isolation, old and new alike. The first section covers the main classes of target cells and compares traditional non-affinity and affinity-based purification techniques, focusing on established ligands and chromatographic formats. The second section presents an excursus of affinity-based pseudo-chromatographic and non-chromatographic technologies, especially focusing on magnetic-activated cell sorting (MACS) and fluorescence-activated cell sorting (FACS). Finally, the third section presents an overview of new technologies and emerging trends, highlighting how the progress in chemical, material, and microfluidic sciences has opened new exciting avenues towards high-throughput and high-purity cell isolation processes. This review is designed to guide scientists and engineers in their choice of suitable cell purification techniques for research or bioprocessing needs.}, journal={ACTA BIOMATERIALIA}, author={Bacon, Kaitlyn and Lavoie, Ashton and Rao, Balaji M. and Daniele, Michael and Menegatti, Stefano}, year={2020}, month={Aug}, pages={29–51} }
 @article{cruz-teran_bacon_rao_2020, title={Simultaneous Soluble Secretion and Surface Display of Proteins in Saccharomyces cerevisiae Using Inefficient Ribosomal Skipping}, volume={2070}, ISBN={["978-1-4939-9852-4"]}, ISSN={["1940-6029"]}, DOI={10.1007/978-1-4939-9853-1_18}, abstractNote={Combinatorial library screening platforms, such as yeast surface display, typically identify several candidate proteins that need further characterization and validation using soluble recombinant protein. However, recombinant production of these candidate proteins involves tedious and time-consuming subcloning steps. This, in turn, limits the number of candidate proteins that can be characterized. To address this bottleneck, we have developed a platform that exploits inefficient ribosomal skipping by the F2A peptide for simultaneous soluble secretion and cell surface display of protein in the yeast Saccharomyces cerevisiae. Here we provide detailed protocols utilizing this F2A-based yeast display system. We discuss specific recommendations for the purification of the secreted protein. Additionally, we provide suggestions for testing the functionality and binding specificity of the soluble secreted proteins using flow cytometry analysis.}, journal={GENOTYPE PHENOTYPE COUPLING: METHODS AND PROTOCOLS}, author={Cruz-Teran, Carlos A. and Bacon, Kaitlyn and Rao, Balaji M.}, year={2020}, pages={321–334} }
 @article{bacon_bowen_reese_rao_menegatti_2020, title={Use of Target-Displaying Magnetized Yeast in Screening mRNA-Display Peptide Libraries to Identify Ligands}, volume={22}, ISSN={["2156-8944"]}, DOI={10.1021/acscombsci.0c00171}, abstractNote={This work presents the first use of yeast-displayed protein targets for screening mRNA-display libraries of cyclic and linear peptides. The WW domains of Yes-Associated Protein 1 (WW-YAP) and mitochondrial import receptor subunit TOM22 were adopted as protein targets. Yeast cells displaying WW-YAP or TOM22 were magnetized with iron oxide nanoparticles to enable the isolation of target-binding mRNA-peptide fusions. Equilibrium adsorption studies were conducted to estimate the binding affinity (KD) of select WW-YAP-binding peptides: KD values of 37 and 4 μM were obtained for cyclo[M-AFRLC-K] and its linear cognate, and 40 and 3 μM for cyclo[M-LDFVNHRSRG-K] and its linear cognate, respectively. TOM22-binding peptide cyclo[M-PELNRAI-K] was conjugated to magnetic beads and incubated with yeast cells expressing TOM22 and luciferase. A luciferase-based assay showed a 4.5-fold higher binding of TOM22+ yeast compared to control cells. This work demonstrates that integrating mRNA- and yeast-display accelerates the discovery of peptide ligands.}, number={12}, journal={ACS COMBINATORIAL SCIENCE}, author={Bacon, Kaitlyn and Bowen, John and Reese, Hannah and Rao, Balaji M. and Menegatti, Stefano}, year={2020}, month={Dec}, pages={738–744} }
 @article{bacon_burroughs_blain_menegatti_rao_2019, title={Screening Yeast Display Libraries against Magnetized Yeast Cell Targets Enables Efficient Isolation of Membrane Protein Binders}, volume={21}, ISSN={["2156-8944"]}, DOI={10.1021/acscombsci.9b00147}, abstractNote={When isolating binders from yeast displayed combinatorial libraries, a soluble, recombinantly expressed form of the target protein is typically utilized. As an alternative, we describe the use of target proteins displayed as surface fusions on magnetized yeast cells. In our strategy, the target protein is coexpressed on the yeast surface with an iron oxide binding protein; incubation of these yeast cells with iron oxide nanoparticles results in their magnetization. Subsequently, binder cells that interact with the magnetized target cells can be isolated using a magnet. Using a known binder–target pair with modest binding affinity (KD ≈ 400 nM), we showed that a binder present at low frequency (1 in 105) could be enriched more than 100-fold, in a single round of screening, suggesting feasibility of screening combinatorial libraries. Subsequently, we screened yeast display libraries of Sso7d and nanobody variants against yeast displayed targets to isolate binders specific to the cytosolic domain of the mitochondrial membrane protein TOM22 (KD ≈ 272–1934 nM) and the extracellular domain of the c-Kit receptor (KD ≈ 93 to KD > 2000 nM). Additional studies showed that the TOM22 binders identified using this approach could be used for the enrichment of mitochondria from cell lysates, thereby confirming binding to the native mitochondrial protein. The ease of expressing a membrane protein or a domain thereof as a yeast cell surface fusion—in contrast to recombinant soluble expression—makes the use of yeast-displayed targets particularly attractive. Therefore, we expect the use of magnetized yeast cell targets will enable efficient isolation of binders to membrane proteins.}, number={12}, journal={ACS COMBINATORIAL SCIENCE}, author={Bacon, Kaitlyn and Burroughs, Matthew and Blain, Abigail and Menegatti, Stefano and Rao, Balaji M.}, year={2019}, month={Dec}, pages={817–832} }