1
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Enninful GN, Kuppusamy R, Tiburu EK, Kumar N, Willcox MDP. Non-canonical amino acid bioincorporation into antimicrobial peptides and its challenges. J Pept Sci 2024; 30:e3560. [PMID: 38262069 DOI: 10.1002/psc.3560] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/06/2023] [Revised: 10/01/2023] [Accepted: 11/14/2023] [Indexed: 01/25/2024]
Abstract
The rise of antimicrobial resistance and multi-drug resistant pathogens has necessitated explorations for novel antibiotic agents as the discovery of conventional antibiotics is becoming economically less viable and technically more challenging for biopharma. Antimicrobial peptides (AMPs) have emerged as a promising alternative because of their particular mode of action, broad spectrum and difficulty that microbes have in becoming resistant to them. The AMPs bacitracin, gramicidin, polymyxins and daptomycin are currently used clinically. However, their susceptibility to proteolytic degradation, toxicity profile, and complexities in large-scale manufacture have hindered their development. To improve their proteolytic stability, methods such as integrating non-canonical amino acids (ncAAs) into their peptide sequence have been adopted, which also improves their potency and spectrum of action. The benefits of ncAA incorporation have been made possible by solid-phase peptide synthesis. However, this method is not always suitable for commercial production of AMPs because of poor yield, scale-up difficulties, and its non-'green' nature. Bioincorporation of ncAA as a method of integration is an emerging field geared towards tackling the challenges of solid-phase synthesis as a green, cheaper, and scalable alternative for commercialisation of AMPs. This review focusses on the bioincorporation of ncAAs; some challenges associated with the methods are outlined, and notes are given on how to overcome these challenges. The review focusses particularly on addressing two key challenges: AMP cytotoxicity towards microbial cell factories and the uptake of ncAAs that are unfavourable to them. Overcoming these challenges will draw us closer to a greater yield and an environmentally friendly and sustainable approach to make AMPs more druggable.
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Affiliation(s)
| | - Rajesh Kuppusamy
- University of New South Wales, Kensington, New South Wales, Australia
| | | | - Naresh Kumar
- University of New South Wales, Kensington, New South Wales, Australia
| | - Mark D P Willcox
- University of New South Wales, Kensington, New South Wales, Australia
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2
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Bednar RM, Karplus PA, Mehl RA. Site-specific dual encoding and labeling of proteins via genetic code expansion. Cell Chem Biol 2023; 30:343-361. [PMID: 36977415 PMCID: PMC10764108 DOI: 10.1016/j.chembiol.2023.03.004] [Citation(s) in RCA: 11] [Impact Index Per Article: 11.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/27/2022] [Revised: 02/10/2023] [Accepted: 03/03/2023] [Indexed: 03/29/2023]
Abstract
The ability to selectively modify proteins at two or more defined locations opens new avenues for manipulating, engineering, and studying living systems. As a chemical biology tool for the site-specific encoding of non-canonical amino acids into proteins in vivo, genetic code expansion (GCE) represents a powerful tool to achieve such modifications with minimal disruption to structure and function through a two-step "dual encoding and labeling" (DEAL) process. In this review, we summarize the state of the field of DEAL using GCE. In doing so, we describe the basic principles of GCE-based DEAL, catalog compatible encoding systems and reactions, explore demonstrated and potential applications, highlight emerging paradigms in DEAL methodologies, and propose novel solutions to current limitations.
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Affiliation(s)
- Riley M Bednar
- Department of Biochemistry and Biophysics, Oregon State University, 2011 Agricultural and Life Sciences Building, Corvallis, OR 97331-7305, USA; GCE4All Research Center, Oregon State University, 2011 Agricultural and Life Sciences, Corvallis, OR 97331-7305, USA
| | - P Andrew Karplus
- Department of Biochemistry and Biophysics, Oregon State University, 2011 Agricultural and Life Sciences Building, Corvallis, OR 97331-7305, USA; GCE4All Research Center, Oregon State University, 2011 Agricultural and Life Sciences, Corvallis, OR 97331-7305, USA
| | - Ryan A Mehl
- Department of Biochemistry and Biophysics, Oregon State University, 2011 Agricultural and Life Sciences Building, Corvallis, OR 97331-7305, USA; GCE4All Research Center, Oregon State University, 2011 Agricultural and Life Sciences, Corvallis, OR 97331-7305, USA.
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3
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Koch NG, Baumann T, Nickling JH, Dziegielewski A, Budisa N. Engineered bacterial host for genetic encoding of physiologically stable protein nitration. Front Mol Biosci 2022; 9:992748. [PMID: 36353730 PMCID: PMC9638147 DOI: 10.3389/fmolb.2022.992748] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/13/2022] [Accepted: 09/16/2022] [Indexed: 11/23/2022] Open
Abstract
Across scales, many biological phenomena, such as protein folding or bioadhesion and cohesion, rely on synergistic effects of different amino acid side chains at multiple positions in the protein sequence. These are often fine-tuned by post-translational modifications that introduce additional chemical properties. Several PTMs can now be genetically encoded and precisely installed at single and multiple sites by genetic code expansion. Protein nitration is a PTM of particular interest because it has been associated with several diseases. However, even when these nitro groups are directly incorporated into proteins, they are often physiologically reduced during or shortly after protein production. We have solved this problem by using an engineered Escherichia coli host strain. Six genes that are associated with nitroreductase activity were removed from the genome in a simple and robust manner. The result is a bacterial expression host that can stably produce proteins and peptides containing nitro groups, especially when these are amenable to modification. To demonstrate the applicability of this strain, we used this host for several applications. One of these was the multisite incorporation of a photocaged 3,4-dihydroxyphenylalanine derivative into Elastin-Like Polypeptides. For this non-canonical amino acid and several other photocaged ncAAs, the nitro group is critical for photocleavability. Accordingly, our approach also enhances the production of biomolecules containing photocaged tyrosine in the form of ortho-nitrobenzyl-tyrosine. We envision our engineered host as an efficient tool for the production of custom designed proteins, peptides or biomaterials for various applications ranging from research in cell biology to large-scale production in biotechnology.
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Affiliation(s)
- Nikolaj G. Koch
- Bioanalytics Group, Institute of Biotechnology, Technische Universität Berlin, Berlin, Germany
- Biocatalysis Group, Institute of Chemistry, Technische Universität Berlin, Berlin, Germany
| | - Tobias Baumann
- Biocatalysis Group, Institute of Chemistry, Technische Universität Berlin, Berlin, Germany
| | - Jessica H. Nickling
- Biocatalysis Group, Institute of Chemistry, Technische Universität Berlin, Berlin, Germany
| | - Anna Dziegielewski
- Biocatalysis Group, Institute of Chemistry, Technische Universität Berlin, Berlin, Germany
| | - Nediljko Budisa
- Biocatalysis Group, Institute of Chemistry, Technische Universität Berlin, Berlin, Germany
- Chemical Synthetic Biology Group, Department of Chemistry, University of Manitoba, Winnipeg, MB, Canada
- *Correspondence: Nediljko Budisa,
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4
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Tittle JM, Schwark DG, Biddle W, Schmitt MA, Fisk JD. Impact of queuosine modification of endogenous E. coli tRNAs on sense codon reassignment. Front Mol Biosci 2022; 9:938114. [PMID: 36120552 PMCID: PMC9471426 DOI: 10.3389/fmolb.2022.938114] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/07/2022] [Accepted: 07/27/2022] [Indexed: 11/13/2022] Open
Abstract
The extent to which alteration of endogenous tRNA modifications may be exploited to improve genetic code expansion efforts has not been broadly investigated. Modifications of tRNAs are strongly conserved evolutionarily, but the vast majority of E. coli tRNA modifications are not essential. We identified queuosine (Q), a non-essential, hypermodified guanosine nucleoside found in position 34 of the anticodons of four E. coli tRNAs as a modification that could potentially be utilized to improve sense codon reassignment. One suggested purpose of queuosine modification is to reduce the preference of tRNAs with guanosine (G) at position 34 of the anticodon for decoding cytosine (C) ending codons over uridine (U) ending codons. We hypothesized that introduced orthogonal translation machinery with adenine (A) at position 34 would reassign U-ending codons more effectively in queuosine-deficient E. coli. We evaluated the ability of introduced orthogonal tRNAs with AUN anticodons to reassign three of the four U-ending codons normally decoded by Q34 endogenous tRNAs: histidine CAU, asparagine AAU, and aspartic acid GAU in the presence and absence of queuosine modification. We found that sense codon reassignment efficiencies in queuosine-deficient strains are slightly improved at Asn AAU, equivalent at His CAU, and less efficient at Asp GAU codons. Utilization of orthogonal pair-directed sense codon reassignment to evaluate competition events that do not occur in the standard genetic code suggests that tRNAs with inosine (I, 6-deaminated A) at position 34 compete much more favorably against G34 tRNAs than Q34 tRNAs. Continued evaluation of sense codon reassignment following targeted alterations to endogenous tRNA modifications has the potential to shed new light on the web of interactions that combine to preserve the fidelity of the genetic code as well as identify opportunities for exploitation in systems with expanded genetic codes.
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5
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New opportunities for genetic code expansion in synthetic yeast. Curr Opin Biotechnol 2022; 75:102691. [DOI: 10.1016/j.copbio.2022.102691] [Citation(s) in RCA: 7] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/01/2021] [Revised: 12/23/2021] [Accepted: 01/18/2022] [Indexed: 12/19/2022]
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6
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Mala P, Saraogi I. Enhanced Codon-Anticodon Interaction at In-Frame UAG Stop Codon Improves the Efficiency of Non-Natural Amino Acid Mutagenesis. ACS Chem Biol 2022; 17:1051-1060. [PMID: 35532803 DOI: 10.1021/acschembio.1c00782] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
The introduction of non-natural amino acids into proteins through the stop codon readthrough methodology has been used to design proteins for diverse applications. However, this method suffers from low yields of the modified protein, as the suppressor tRNA that recognizes the stop codon is unable to compete effectively with release factor 1 (RF1), which terminates translation. We reasoned that a suppressor tRNA with improved interaction with the UAG stop codon on the mRNA will be able to compete more effectively with RF1. To test this idea, we inserted two 2,6-diaminopurine (D) units in the tRNA anticodon stem loop, including one at the third position of the tRNA anticodon. The modified suppressor tRNA could potentially form additional H-bonds between the N2-exocyclic amine of D and the C2 carbonyl group of uracil, thereby enhancing mRNA-tRNA interaction and/or altering tRNA conformation. The stronger interaction at the codon-anticodon interface resulted in improved UAG decoding efficiency and a higher yield of the modified protein containing a non-natural amino acid at multiple sites. Our findings are consistent with the importance of hydrogen bonding and tRNA conformation at the tRNA-mRNA duplex interface during in-frame UAG suppression, which improves protein translation at multiple UAG stop sites. This work provides valuable inputs toward improved non-natural amino acid mutagenesis for creating designer proteins.
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Affiliation(s)
- Purnima Mala
- Department of Biological Sciences, Indian Institute of Science Education and Research Bhopal, Bhopal 462066, India
| | - Ishu Saraogi
- Department of Biological Sciences, Indian Institute of Science Education and Research Bhopal, Bhopal 462066, India
- Department of Chemistry, Indian Institute of Science Education and Research Bhopal, Bhopal 462066, India
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7
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Engineering Proteins Containing Noncanonical Amino Acids on the Yeast Surface. METHODS IN MOLECULAR BIOLOGY (CLIFTON, N.J.) 2022; 2491:491-559. [PMID: 35482204 DOI: 10.1007/978-1-0716-2285-8_23] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
Yeast display has been used to advance many critical research areas, including the discovery of unique protein binders and biological therapeutics. In parallel, noncanonical amino acids (ncAAs) have been used to tailor antibody-drug conjugates and enable discovery of therapeutic leads. Together, these two technologies have allowed for generation of synthetic antibody libraries, where the introduction of ncAAs in yeast-displayed proteins allows for library screening for therapeutically relevant targets. The combination of yeast display with genetically encoded ncAAs increases the available chemistry in proteins and advances applications that require high-throughput strategies. In this chapter, we discuss methods for displaying proteins containing ncAAs on the yeast surface, generating and screening libraries of proteins containing ncAAs, preparing bioconjugates on the yeast surface in large scale, generating and screening libraries of aminoacyl-tRNA synthetases (aaRSs) for encoding ncAAs by using reporter constructs, and characterizing ncAA-containing proteins secreted from yeast. The experimental designs laid out in this chapter are generalizable for discovery of protein binders to a variety of targets and aaRS evolution to continue expanding the genetic code beyond what is currently available in yeast.
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8
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Koch NG, Baumann T, Budisa N. Efficient Unnatural Protein Production by Pyrrolysyl-tRNA Synthetase With Genetically Fused Solubility Tags. Front Bioeng Biotechnol 2022; 9:807438. [PMID: 35284428 PMCID: PMC8905625 DOI: 10.3389/fbioe.2021.807438] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/02/2021] [Accepted: 11/17/2021] [Indexed: 11/27/2022] Open
Abstract
Introducing non-canonical amino acids (ncAAs) by engineered orthogonal pairs of aminoacyl-tRNA synthetases and tRNAs has proven to be a highly useful tool for the expansion of the genetic code. Pyrrolysyl-tRNA synthetase (PylRS) from methanogenic archaeal and bacterial species is particularly attractive due to its natural orthogonal reactivity in bacterial and eukaryotic cells. However, the scope of such a reprogrammed translation is often limited, due to low yields of chemically modified target protein. This can be the result of substrate specificity engineering, which decreases the aminoacyl-tRNA synthetase stability and reduces the abundance of active enzyme. We show that the solubility and folding of these engineered enzymes can become a bottleneck for the production of ncAA-containing proteins in vivo. Solubility tags derived from various species provide a strategy to remedy this issue. We find the N-terminal fusion of the small metal binding protein from Nitrosomonas europaea to the PylRS sequence to improve enzyme solubility and to boost orthogonal translation efficiency. Our strategy enhances the production of site-specifically labelled proteins with a variety of engineered PylRS variants by 200–540%, and further allows triple labeling. Even the wild-type enzyme gains up to 245% efficiency for established ncAA substrates.
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Affiliation(s)
- Nikolaj G Koch
- Biokatalyse, Institut für Chemie, Technische Universität Berlin, Berlin, Germany.,Bioanalytik, Institut für Biotechnologie, Technische Universität Berlin, Berlin, Germany
| | - Tobias Baumann
- Biokatalyse, Institut für Chemie, Technische Universität Berlin, Berlin, Germany
| | - Nediljko Budisa
- Biokatalyse, Institut für Chemie, Technische Universität Berlin, Berlin, Germany.,Chemical Synthetic Biology, Department of Chemistry, University of Manitoba, Winnipeg, MB, Canada
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9
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Biddle W, Schwark DG, Schmitt MA, Fisk JD. Directed Evolution Pipeline for the Improvement of Orthogonal Translation Machinery for Genetic Code Expansion at Sense Codons. Front Chem 2022; 10:815788. [PMID: 35252113 PMCID: PMC8891652 DOI: 10.3389/fchem.2022.815788] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/15/2021] [Accepted: 01/24/2022] [Indexed: 12/30/2022] Open
Abstract
The expansion of the genetic code beyond a single type of noncanonical amino acid (ncAA) is hindered by inefficient machinery for reassigning the meaning of sense codons. A major obstacle to using directed evolution to improve the efficiency of sense codon reassignment is that fractional sense codon reassignments lead to heterogeneous mixtures of full-length proteins with either a ncAA or a natural amino acid incorporated in response to the targeted codon. In stop codon suppression systems, missed incorporations lead to truncated proteins; improvements in activity may be inferred from increased protein yields or the production of downstream reporters. In sense codon reassignment, the heterogeneous proteins produced greatly complicate the development of screens for variants of the orthogonal machinery with improved activity. We describe the use of a previously-reported fluorescence-based screen for sense codon reassignment as the first step in a directed evolution workflow to improve the incorporation of a ncAA in response to the Arg AGG sense codon. We first screened a library with diversity introduced into both the orthogonal Methanocaldococcus jannaschii tyrosyl tRNA anticodon loop and the cognate aminoacyl tRNA synthetase (aaRS) anticodon binding domain for variants that improved incorporation of tyrosine in response to the AGG codon. The most efficient variants produced fluorescent proteins at levels indistinguishable from the E. coli translation machinery decoding tyrosine codons. Mutations to the M. jannaschii aaRS that were found to improve tyrosine incorporation were transplanted onto a M. jannaschii aaRS evolved for the incorporation of para-azidophenylalanine. Improved ncAA incorporation was evident using fluorescence- and mass-based reporters. The described workflow is generalizable and should enable the rapid tailoring of orthogonal machinery capable of activating diverse ncAAs to any sense codon target. We evaluated the selection based improvements of the orthogonal pair in a host genomically engineered for reduced target codon competition. Using this particular system for evaluation of arginine AGG codon reassignment, however, E. coli strains with genomes engineered to remove competing tRNAs did not outperform a standard laboratory E. coli strain in sense codon reassignment.
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10
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Lateef OM, Akintubosun MO, Olaoba OT, Samson SO, Adamczyk M. Making Sense of "Nonsense" and More: Challenges and Opportunities in the Genetic Code Expansion, in the World of tRNA Modifications. Int J Mol Sci 2022; 23:938. [PMID: 35055121 PMCID: PMC8779196 DOI: 10.3390/ijms23020938] [Citation(s) in RCA: 5] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/02/2021] [Revised: 01/10/2022] [Accepted: 01/12/2022] [Indexed: 01/09/2023] Open
Abstract
The evolutional development of the RNA translation process that leads to protein synthesis based on naturally occurring amino acids has its continuation via synthetic biology, the so-called rational bioengineering. Genetic code expansion (GCE) explores beyond the natural translational processes to further enhance the structural properties and augment the functionality of a wide range of proteins. Prokaryotic and eukaryotic ribosomal machinery have been proven to accept engineered tRNAs from orthogonal organisms to efficiently incorporate noncanonical amino acids (ncAAs) with rationally designed side chains. These side chains can be reactive or functional groups, which can be extensively utilized in biochemical, biophysical, and cellular studies. Genetic code extension offers the contingency of introducing more than one ncAA into protein through frameshift suppression, multi-site-specific incorporation of ncAAs, thereby increasing the vast number of possible applications. However, different mediating factors reduce the yield and efficiency of ncAA incorporation into synthetic proteins. In this review, we comment on the recent advancements in genetic code expansion to signify the relevance of systems biology in improving ncAA incorporation efficiency. We discuss the emerging impact of tRNA modifications and metabolism in protein design. We also provide examples of the latest successful accomplishments in synthetic protein therapeutics and show how codon expansion has been employed in various scientific and biotechnological applications.
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Affiliation(s)
- Olubodun Michael Lateef
- Faculty of Chemistry, Warsaw University of Technology, 00-664 Warsaw, Poland; (O.M.L.); (M.O.A.); (S.O.S.)
| | | | - Olamide Tosin Olaoba
- Laboratory of Functional and Structural Biochemistry, Federal University of Sao Carlos, Sao Carlos 13565-905, SP, Brazil;
| | - Sunday Ocholi Samson
- Faculty of Chemistry, Warsaw University of Technology, 00-664 Warsaw, Poland; (O.M.L.); (M.O.A.); (S.O.S.)
| | - Malgorzata Adamczyk
- Faculty of Chemistry, Warsaw University of Technology, 00-664 Warsaw, Poland; (O.M.L.); (M.O.A.); (S.O.S.)
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11
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Vistrup-Parry M, Chen X, Johansen TL, Bach S, Buch-Larsen SC, Bartling CRO, Ma C, Clemmensen LS, Nielsen ML, Zhang M, Strømgaard K. Site-specific phosphorylation of PSD-95 dynamically regulates the postsynaptic density as observed by phase separation. iScience 2021; 24:103268. [PMID: 34761188 PMCID: PMC8567388 DOI: 10.1016/j.isci.2021.103268] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/08/2020] [Revised: 01/11/2021] [Accepted: 10/12/2021] [Indexed: 01/06/2023] Open
Abstract
Postsynaptic density protein 95 is a key scaffolding protein in the postsynaptic density of excitatory glutamatergic neurons, organizing signaling complexes primarily via its three PSD-95/Discs-large/Zona occludens domains. PSD-95 is regulated by phosphorylation, but technical challenges have limited studies of the molecular details. Here, we genetically introduced site-specific phosphorylations in single, tandem, and full-length PSD-95 and generated a total of 11 phosphorylated protein variants. We examined how these phosphorylations affected binding to known interaction partners and the impact on phase separation of PSD-95 complexes and identified two new phosphorylation sites with opposing effects. Phosphorylation of Ser78 inhibited phase separation with the glutamate receptor subunit GluN2B and the auxiliary protein stargazin, whereas phosphorylation of Ser116 induced phase separation with stargazin only. Thus, by genetically introducing phosphoserine site-specifically and exploring the impact on phase separation, we have provided new insights into the regulation of PSD-95 by phosphorylation and the dynamics of the PSD.
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Affiliation(s)
- Maria Vistrup-Parry
- Center for Biopharmaceuticals, Department of Drug Design and Pharmacology, University of Copenhagen, Jagtvej 162, 2100 Copenhagen, Denmark
| | - Xudong Chen
- Division of Life Science, State Key Laboratory of Molecular Neuroscience, Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong, China
| | - Thea L Johansen
- Center for Biopharmaceuticals, Department of Drug Design and Pharmacology, University of Copenhagen, Jagtvej 162, 2100 Copenhagen, Denmark
| | - Sofie Bach
- Center for Biopharmaceuticals, Department of Drug Design and Pharmacology, University of Copenhagen, Jagtvej 162, 2100 Copenhagen, Denmark
| | - Sara C Buch-Larsen
- Proteomics Program, Novo Nordisk Foundation Center for Protein Research, University of Copenhagen, Blegdamsvej 3B, 2200 Copenhagen, Denmark
| | - Christian R O Bartling
- Center for Biopharmaceuticals, Department of Drug Design and Pharmacology, University of Copenhagen, Jagtvej 162, 2100 Copenhagen, Denmark
| | - Chenxue Ma
- Division of Life Science, State Key Laboratory of Molecular Neuroscience, Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong, China
| | - Louise S Clemmensen
- Center for Biopharmaceuticals, Department of Drug Design and Pharmacology, University of Copenhagen, Jagtvej 162, 2100 Copenhagen, Denmark
| | - Michael L Nielsen
- Proteomics Program, Novo Nordisk Foundation Center for Protein Research, University of Copenhagen, Blegdamsvej 3B, 2200 Copenhagen, Denmark
| | - Mingjie Zhang
- Division of Life Science, State Key Laboratory of Molecular Neuroscience, Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong, China.,Shenzhen Bay Laboratory, Gaoke Innovation Center, Guangqiao Road, Guangming District, Shenzhen, China
| | - Kristian Strømgaard
- Center for Biopharmaceuticals, Department of Drug Design and Pharmacology, University of Copenhagen, Jagtvej 162, 2100 Copenhagen, Denmark
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12
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Bartoschek MD, Ugur E, Nguyen TA, Rodschinka G, Wierer M, Lang K, Bultmann S. Identification of permissive amber suppression sites for efficient non-canonical amino acid incorporation in mammalian cells. Nucleic Acids Res 2021; 49:e62. [PMID: 33684219 PMCID: PMC8216290 DOI: 10.1093/nar/gkab132] [Citation(s) in RCA: 25] [Impact Index Per Article: 8.3] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/22/2020] [Revised: 02/16/2021] [Accepted: 02/17/2021] [Indexed: 12/20/2022] Open
Abstract
The genetic code of mammalian cells can be expanded to allow the incorporation of non-canonical amino acids (ncAAs) by suppressing in-frame amber stop codons (UAG) with an orthogonal pyrrolysyl-tRNA synthetase (PylRS)/tRNAPylCUA (PylT) pair. However, the feasibility of this approach is substantially hampered by unpredictable variations in incorporation efficiencies at different stop codon positions within target proteins. Here, we apply a proteomics-based approach to quantify ncAA incorporation rates at hundreds of endogenous amber stop codons in mammalian cells. With these data, we compute iPASS (Identification of Permissive Amber Sites for Suppression; available at www.bultmannlab.eu/tools/iPASS), a linear regression model to predict relative ncAA incorporation efficiencies depending on the surrounding sequence context. To verify iPASS, we develop a dual-fluorescence reporter for high-throughput flow-cytometry analysis that reproducibly yields context-specific ncAA incorporation efficiencies. We show that nucleotides up- and downstream of UAG synergistically influence ncAA incorporation efficiency independent of cell line and ncAA identity. Additionally, we demonstrate iPASS-guided optimization of ncAA incorporation rates by synonymous exchange of codons flanking the amber stop codon. This combination of in silico analysis followed by validation in living mammalian cells substantially simplifies identification as well as adaptation of sites within a target protein to confer high ncAA incorporation rates.
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Affiliation(s)
- Michael D Bartoschek
- Department of Biology II and Center for Molecular Biosystems (BioSysM), Human Biology and BioImaging, Ludwig-Maximilians-Universität München, Munich 81377, Germany
| | - Enes Ugur
- Department of Biology II and Center for Molecular Biosystems (BioSysM), Human Biology and BioImaging, Ludwig-Maximilians-Universität München, Munich 81377, Germany.,Department of Proteomics and Signal Transduction, Max Planck Institute of Biochemistry, Martinsried 82152, Germany
| | - Tuan-Anh Nguyen
- Department of Chemistry, Synthetic Biochemistry, Technical University of Munich, Garching 85748, Germany
| | - Geraldine Rodschinka
- Department of Biology II and Center for Molecular Biosystems (BioSysM), Human Biology and BioImaging, Ludwig-Maximilians-Universität München, Munich 81377, Germany
| | - Michael Wierer
- Department of Proteomics and Signal Transduction, Max Planck Institute of Biochemistry, Martinsried 82152, Germany
| | - Kathrin Lang
- Department of Chemistry, Synthetic Biochemistry, Technical University of Munich, Garching 85748, Germany
| | - Sebastian Bultmann
- Department of Biology II and Center for Molecular Biosystems (BioSysM), Human Biology and BioImaging, Ludwig-Maximilians-Universität München, Munich 81377, Germany
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13
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Porter JJ, Heil CS, Lueck JD. Therapeutic promise of engineered nonsense suppressor tRNAs. WILEY INTERDISCIPLINARY REVIEWS. RNA 2021; 12:e1641. [PMID: 33567469 PMCID: PMC8244042 DOI: 10.1002/wrna.1641] [Citation(s) in RCA: 35] [Impact Index Per Article: 11.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 07/11/2020] [Revised: 12/16/2020] [Accepted: 12/23/2020] [Indexed: 12/11/2022]
Abstract
Nonsense mutations change an amino acid codon to a premature termination codon (PTC) generally through a single-nucleotide substitution. The generation of a PTC results in a defective truncated protein and often in severe forms of disease. Because of the exceedingly high prevalence of nonsense-associated diseases and a unifying mechanism, there has been a concerted effort to identify PTC therapeutics. Most clinical trials for PTC therapeutics have been conducted with small molecules that promote PTC read through and incorporation of a near-cognate amino acid. However, there is a need for PTC suppression agents that recode PTCs with the correct amino acid while being applicable to PTC mutations in many different genomic landscapes. With these characteristics, a single therapeutic will be able to treat several disease-causing PTCs. In this review, we will focus on the use of nonsense suppression technologies, in particular, suppressor tRNAs (sup-tRNAs), as possible therapeutics for correcting PTCs. Sup-tRNAs have many attractive qualities as possible therapeutic agents although there are knowledge gaps on their function in mammalian cells and technical hurdles that need to be overcome before their promise is realized. This article is categorized under: RNA Processing > tRNA Processing Translation > Translation Regulation.
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Affiliation(s)
- Joseph J. Porter
- Department of Pharmacology and PhysiologyUniversity of Rochester Medical CenterRochesterNew YorkUSA
| | - Christina S. Heil
- Department of Pharmacology and PhysiologyUniversity of Rochester Medical CenterRochesterNew YorkUSA
| | - John D. Lueck
- Department of Pharmacology and PhysiologyUniversity of Rochester Medical CenterRochesterNew YorkUSA
- Department of NeurologyUniversity of Rochester Medical CenterRochesterNew YorkUSA
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14
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Dangerfield TL, Johnson KA. Optimized incorporation of an unnatural fluorescent amino acid affords measurement of conformational dynamics governing high-fidelity DNA replication. J Biol Chem 2020; 295:17265-17280. [PMID: 33020184 PMCID: PMC7863912 DOI: 10.1074/jbc.ra120.015557] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/10/2020] [Revised: 09/29/2020] [Indexed: 12/20/2022] Open
Abstract
DNA polymerase from bacteriophage T7 undergoes large, substrate-induced conformational changes that are thought to account for high replication fidelity, but prior studies were adversely affected by mutations required to construct a Cys-lite variant needed for site-specific fluorescence labeling. Here we have optimized the direct incorporation of a fluorescent un-natural amino acid, (7-hydroxy-4-coumarin-yl)-ethylglycine, using orthogonal amber suppression machinery in Escherichia coli MS methods verify that the unnatural amino acid is only incorporated at one position with minimal background. We show that the single fluorophore provides a signal to detect nucleotide-induced conformational changes through equilibrium and stopped-flow kinetic measurements of correct nucleotide binding and incorporation. Pre-steady-state chemical quench methods show that the kinetics and fidelity of DNA replication catalyzed by the labeled enzyme are largely unaffected by the unnatural amino acid. These advances enable rigorous analysis to establish the kinetic and mechanistic basis for high-fidelity DNA replication.
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Affiliation(s)
- Tyler L Dangerfield
- Institute for Cellular and Molecular Biology, Department of Molecular Biosciences, University of Texas, Austin, Texas, USA
| | - Kenneth A Johnson
- Institute for Cellular and Molecular Biology, Department of Molecular Biosciences, University of Texas, Austin, Texas, USA.
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15
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van Husen LS, Schedin-Weiss S, Trung MN, Kazmi MA, Winblad B, Sakmar TP, Elsässer SJ, Tjernberg LO. Dual Bioorthogonal Labeling of the Amyloid-β Protein Precursor Facilitates Simultaneous Visualization of the Protein and Its Cleavage Products. J Alzheimers Dis 2020; 72:537-548. [PMID: 31609694 PMCID: PMC6918917 DOI: 10.3233/jad-190898] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
Abstract
The amyloid-β protein precursor (AβPP) is critical in the pathophysiology of Alzheimer’s disease (AD), since two-step proteolytic processing of AβPP generates the neurotoxic amyloid-β peptide (Aβ). We developed a dual fluorescence labeling system to study the exact subcellular location of γ-secretase cleavage of AβPP. The C-terminal tail of AβPP was fluorescently labeled using a SNAP-tag, while the Aβ region of AβPP was fluorescently tagged with a dye at a genetically-encoded noncanonical amino acid (ncAA). The ncAA was introduced at specific positions in AβPP using a genetic code expansion strategy and afterwards, the reactive side-chain of the ncAA was coupled to the dye using a bioorthogonal labeling chemistry. In proof-of-concept experiments, HEK293T cells were transfected with plasmids containing engineered AβPP harboring an amber mutation and an amber codon suppression system with an evolved tRNA synthetase/tRNA pair and grown in the presence of a lysine-derived ncAA. Processing of the AβPP variants was validated with ELISA and immunoblotting, and seven AβPP mutants that showed similar cleavage pattern as wild-type AβPP were identified. The AβPP mutant was fluorescently labeled with 6-methyl-tetrazine-BDP-FL and TMR-Star at the ncAA and SNAP-tag, respectively. Using this approach, AβPP was fluorescently labeled at two sites in living cells with minimal background to allow monitoring of Aβ and C-terminal cleavage products simultaneously. The method described provides a powerful tool to label Aβ with minimal perturbations of its processing, thus enabling studies of the trafficking of the cleavage products of AβPP.
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Affiliation(s)
- Lea S van Husen
- Center for Alzheimer Research, Division of Neurogeriatrics, Department of Neurobiology, Care Sciences, and Society, Karolinska Institutet, Solna, Sweden
| | - Sophia Schedin-Weiss
- Center for Alzheimer Research, Division of Neurogeriatrics, Department of Neurobiology, Care Sciences, and Society, Karolinska Institutet, Solna, Sweden
| | - Minh Nguyen Trung
- Leibniz-Forschungsinstitut für Molekulare Pharmakologie, Berlin, Germany.,Institute of Chemistry, Humboldt-Universität zu Berlin, Berlin, Germany
| | - Manija A Kazmi
- Laboratory of Chemical Biology & Signal Transduction, The Rockefeller University, New York, NY, USA
| | - Bengt Winblad
- Center for Alzheimer Research, Division of Neurogeriatrics, Department of Neurobiology, Care Sciences, and Society, Karolinska Institutet, Solna, Sweden.,Karolinska University Hospital, Theme Aging, Stockholm, Sweden
| | - Thomas P Sakmar
- Center for Alzheimer Research, Division of Neurogeriatrics, Department of Neurobiology, Care Sciences, and Society, Karolinska Institutet, Solna, Sweden.,Laboratory of Chemical Biology & Signal Transduction, The Rockefeller University, New York, NY, USA
| | - Simon J Elsässer
- Science for Life Laboratory, Department of Medical Biochemistry and Biophysics, Karolinska Institutet, Stockholm, Sweden.,Ming Wai Lau Centre for Reparative Medicine, Stockholm Node, Karolinska Institutet, Stockholm, Sweden
| | - Lars O Tjernberg
- Center for Alzheimer Research, Division of Neurogeriatrics, Department of Neurobiology, Care Sciences, and Society, Karolinska Institutet, Solna, Sweden
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16
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Pérez-Mejías G, Velázquez-Cruz A, Guerra-Castellano A, Baños-Jaime B, Díaz-Quintana A, González-Arzola K, Ángel De la Rosa M, Díaz-Moreno I. Exploring protein phosphorylation by combining computational approaches and biochemical methods. Comput Struct Biotechnol J 2020; 18:1852-1863. [PMID: 32728408 PMCID: PMC7369424 DOI: 10.1016/j.csbj.2020.06.043] [Citation(s) in RCA: 24] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/30/2020] [Revised: 06/29/2020] [Accepted: 06/30/2020] [Indexed: 12/14/2022] Open
Abstract
Post-translational modifications of proteins expand their functional diversity, regulating the response of cells to a variety of stimuli. Among these modifications, phosphorylation is the most ubiquitous and plays a prominent role in cell signaling. The addition of a phosphate often affects the function of a protein by altering its structure and dynamics. However, these alterations are often difficult to study and the functional and structural implications remain unresolved. New approaches are emerging to overcome common obstacles related to the production and manipulation of these samples. Here, we summarize the available methods for phosphoprotein purification and phosphomimetic engineering, highlighting the advantages and disadvantages of each. We propose a general workflow for protein phosphorylation analysis combining computational and biochemical approaches, building on recent advances that enable user-friendly and easy-to-access Molecular Dynamics simulations. We hope this innovative workflow will inform the best experimental approach to explore such post-translational modifications. We have applied this workflow to two different human protein models: the hemeprotein cytochrome c and the RNA binding protein HuR. Our results illustrate the usefulness of Molecular Dynamics as a decision-making tool to design the most appropriate phosphomimetic variant.
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Affiliation(s)
- Gonzalo Pérez-Mejías
- Instituto de Investigaciones Químicas (IIQ), Centro de Investigaciones Científicas Isla de la Cartuja (cicCartuja), Universidad de Sevilla, Consejo Superior de Investigaciones Científicas (CSIC), Avda., Américo Vespucio 49, Sevilla 41092, Spain
| | - Alejandro Velázquez-Cruz
- Instituto de Investigaciones Químicas (IIQ), Centro de Investigaciones Científicas Isla de la Cartuja (cicCartuja), Universidad de Sevilla, Consejo Superior de Investigaciones Científicas (CSIC), Avda., Américo Vespucio 49, Sevilla 41092, Spain
| | - Alejandra Guerra-Castellano
- Instituto de Investigaciones Químicas (IIQ), Centro de Investigaciones Científicas Isla de la Cartuja (cicCartuja), Universidad de Sevilla, Consejo Superior de Investigaciones Científicas (CSIC), Avda., Américo Vespucio 49, Sevilla 41092, Spain
| | - Blanca Baños-Jaime
- Instituto de Investigaciones Químicas (IIQ), Centro de Investigaciones Científicas Isla de la Cartuja (cicCartuja), Universidad de Sevilla, Consejo Superior de Investigaciones Científicas (CSIC), Avda., Américo Vespucio 49, Sevilla 41092, Spain
| | - Antonio Díaz-Quintana
- Instituto de Investigaciones Químicas (IIQ), Centro de Investigaciones Científicas Isla de la Cartuja (cicCartuja), Universidad de Sevilla, Consejo Superior de Investigaciones Científicas (CSIC), Avda., Américo Vespucio 49, Sevilla 41092, Spain
| | - Katiuska González-Arzola
- Instituto de Investigaciones Químicas (IIQ), Centro de Investigaciones Científicas Isla de la Cartuja (cicCartuja), Universidad de Sevilla, Consejo Superior de Investigaciones Científicas (CSIC), Avda., Américo Vespucio 49, Sevilla 41092, Spain
| | - Miguel Ángel De la Rosa
- Instituto de Investigaciones Químicas (IIQ), Centro de Investigaciones Científicas Isla de la Cartuja (cicCartuja), Universidad de Sevilla, Consejo Superior de Investigaciones Científicas (CSIC), Avda., Américo Vespucio 49, Sevilla 41092, Spain
| | - Irene Díaz-Moreno
- Instituto de Investigaciones Químicas (IIQ), Centro de Investigaciones Científicas Isla de la Cartuja (cicCartuja), Universidad de Sevilla, Consejo Superior de Investigaciones Científicas (CSIC), Avda., Américo Vespucio 49, Sevilla 41092, Spain
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17
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Schwark DG, Schmitt MA, Biddle W, Fisk JD. The Influence of Competing tRNA Abundance on Translation: Quantifying the Efficiency of Sense Codon Reassignment at Rarely Used Codons. Chembiochem 2020; 21:2274-2286. [PMID: 32203635 DOI: 10.1002/cbic.202000052] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/29/2020] [Revised: 03/12/2020] [Indexed: 11/07/2022]
Abstract
A quantitative understanding of how system composition and molecular properties conspire to determine the fidelity of translation is lacking. Our strategy directs an orthogonal tRNA to directly compete against endogenous tRNAs to decode individual targeted codons in a GFP reporter. Sets of directed sense codon reassignment measurements allow the isolation of particular factors contributing to translational fidelity. In this work, we isolated the effect of tRNA concentration on translational fidelity by evaluating reassignment of the 15 least commonly employed E. coli sense codons. Eight of the rarely used codons are reassigned with greater than 20 % efficiency. Both tRNA abundance and codon demand moderately inversely correlate with reassignment efficiency. Furthermore, the reassignment of rarely used codons does not appear to confer a fitness advantage relative to reassignment of other codons. These direct competition experiments also map potential targets for genetic code expansion. The isoleucine AUA codon is particularly attractive for the incorporation of noncanonical amino acids, with a nonoptimized reassignment efficiency of nearly 70 %.
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Affiliation(s)
- David G Schwark
- Department of Chemistry, University of Colorado Denver Campus Box 194, P.O. Box 173364, Denver, CO 80217-3364, USA
| | - Margaret A Schmitt
- Department of Chemistry, University of Colorado Denver Campus Box 194, P.O. Box 173364, Denver, CO 80217-3364, USA
| | - Wil Biddle
- Department of Chemistry, University of Colorado Denver Campus Box 194, P.O. Box 173364, Denver, CO 80217-3364, USA
| | - John D Fisk
- Department of Chemistry, University of Colorado Denver Campus Box 194, P.O. Box 173364, Denver, CO 80217-3364, USA
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18
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New codons for efficient production of unnatural proteins in a semisynthetic organism. Nat Chem Biol 2020; 16:570-576. [PMID: 32251411 PMCID: PMC7263176 DOI: 10.1038/s41589-020-0507-z] [Citation(s) in RCA: 39] [Impact Index Per Article: 9.8] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/12/2019] [Revised: 01/20/2020] [Accepted: 02/25/2020] [Indexed: 12/02/2022]
Abstract
Natural organisms use a four-letter genetic alphabet that makes available
64 triplet codons, of which 61 are sense codons used to encode proteins with the
20 canonical amino acids. We have shown that the unnatural nucleotides dNaM and
dTPT3 pair to form an unnatural base pair (UBP) and allow for the creation of
semi-synthetic organisms (SSOs) with additional sense codons. Here we report a
systematic analysis of the unnatural codons. We identify nine unnatural codons
that can produce unnatural protein with nearly complete incorporation of an
encoded non-canonical amino acid (ncAA). We also show that at least three of the
codons are orthogonal and can be simultaneously decoded in the SSO, affording
the first 67-codon organism. The ability to site-specifically incorporate
multiple, different ncAAs into a protein should now allow for the development of
proteins with novel activities and possibly even SSOs with new forms and
functions.
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19
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Potts KA, Stieglitz JT, Lei M, Van Deventer JA. Reporter system architecture affects measurements of noncanonical amino acid incorporation efficiency and fidelity. MOLECULAR SYSTEMS DESIGN & ENGINEERING 2020; 5:573-588. [PMID: 33791108 PMCID: PMC8009230 DOI: 10.1039/c9me00107g] [Citation(s) in RCA: 13] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/03/2023]
Abstract
The ability to genetically encode noncanonical amino acids (ncAAs) within proteins supports a growing number of applications ranging from fundamental biological studies to enhancing the properties of biological therapeutics. Currently, our quantitative understanding of ncAA incorporation systems is confounded by the diverse set of characterization and analysis approaches used to quantify ncAA incorporation events. While several effective reporter systems support such measurements, it is not clear how quantitative results from different reporters relate to one another, or which details influence measurements most strongly. Here, we evaluate the quantitative performance of single-fluorescent protein reporters, dual-fluorescent protein reporters, and cell surface-displayed protein reporters of ncAA insertion in response to the TAG (amber) codon in yeast. While different reporters support varying levels of apparent readthrough efficiencies, flow cytometry-based evaluations with dual reporters yielded measurements exhibiting consistent quantitative trends and precision across all evaluated conditions. Further investigations of dual-fluorescent protein reporter architecture revealed that quantitative outputs are influenced by stop codon location and N- and C-terminal fluorescent protein identity. Both dual-fluorescent protein reporters and a "drop-in" version of yeast display support quantification of ncAA incorporation in several single-gene knockout strains, revealing strains that enhance ncAA incorporation efficiency without compromising fidelity. Our studies reveal critical details regarding reporter system performance in yeast and how to effectively deploy such reporters. These findings have substantial implications for how to engineer ncAA incorporation systems-and protein translation apparatuses-to better accommodate alternative genetic codes for expanding the chemical diversity of biosynthesized proteins.
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Affiliation(s)
- K A Potts
- Chemical and Biological Engineering Department, Tufts University, Medford, Massachusetts 02155, United States
| | - J T Stieglitz
- Chemical and Biological Engineering Department, Tufts University, Medford, Massachusetts 02155, United States
| | - M Lei
- Chemical and Biological Engineering Department, Tufts University, Medford, Massachusetts 02155, United States
| | - J A Van Deventer
- Chemical and Biological Engineering Department, Tufts University, Medford, Massachusetts 02155, United States
- Biomedical Engineering Department, Tufts University, Medford, Massachusetts 02155, United States
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20
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Israeli B, Vaserman L, Amiram M. Multi‐Site Incorporation of Nonstandard Amino Acids into Protein‐Based Biomaterials. Isr J Chem 2019. [DOI: 10.1002/ijch.201900043] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022]
Affiliation(s)
- Bar Israeli
- Avram and Stella Goldstein-Goren Department of Biotechnology Engineering Ben-Gurion University of the Negev Beer-Sheva Israel
| | - Livne Vaserman
- Avram and Stella Goldstein-Goren Department of Biotechnology Engineering Ben-Gurion University of the Negev Beer-Sheva Israel
| | - Miriam Amiram
- Avram and Stella Goldstein-Goren Department of Biotechnology Engineering Ben-Gurion University of the Negev Beer-Sheva Israel
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21
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O'Donoghue P, Heinemann IU. Synthetic DNA and RNA Programming. Genes (Basel) 2019; 10:genes10070523. [PMID: 31336805 PMCID: PMC6678149 DOI: 10.3390/genes10070523] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/26/2019] [Accepted: 07/02/2019] [Indexed: 02/05/2023] Open
Abstract
Synthetic biology is a broad and emerging discipline that capitalizes on recent advances in molecular biology, genetics, protein and RNA engineering as well as omics technologies. Together these technologies have transformed our ability to reveal the biology of the cell and the molecular basis of disease. This Special Issue on "Synthetic RNA and DNA Programming" features original research articles and reviews, highlighting novel aspects of basic molecular biology and the molecular mechanisms of disease that were uncovered by the application and development of novel synthetic biology-driven approaches.
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Affiliation(s)
- Patrick O'Donoghue
- Department of Biochemistry, The University of Western Ontario, London, ON N6A 5C1, Canada.
- Department of Chemistry, The University of Western Ontario, London, ON N6A 5C1, Canada.
| | - Ilka U Heinemann
- Department of Biochemistry, The University of Western Ontario, London, ON N6A 5C1, Canada.
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