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DasGupta S. Synthetic antibodies for accelerated RNA crystallography. WILEY INTERDISCIPLINARY REVIEWS. RNA 2024; 15:e1869. [PMID: 39187256 DOI: 10.1002/wrna.1869] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/28/2024] [Revised: 07/04/2024] [Accepted: 07/25/2024] [Indexed: 08/28/2024]
Abstract
RNA structure is crucial to a wide range of cellular processes. The intimate relationship between macromolecular structure and function necessitates the determination of high-resolution structures of functional RNA molecules. X-ray crystallography is the predominant technique used for macromolecular structure determination; however, solving RNA structures has been more challenging than their protein counterparts, as reflected in their poor representation in the Protein Data Bank (<1%). Antibody-assisted RNA crystallography is a relatively new technique that promises to accelerate RNA structure determination by employing synthetic antibodies (Fabs) as crystallization chaperones that are specifically raised against target RNAs. Antibody chaperones facilitate the formation of ordered crystal lattices by minimizing RNA flexibility and replacing unfavorable RNA-RNA contacts with contacts between chaperone molecules. Atomic coordinates of these antibody fragments can also be used as search models to obtain phase information during structure determination. Antibody-assisted RNA crystallography has enabled the structure determination of 15 unique RNA targets, including 11 in the last 6 years. In this review, I cover the historical development of antibody fragments as crystallization chaperones and their application to diverse RNA targets. I discuss how the first structures of antibody-RNA complexes informed the design of second-generation antibodies and led to the development of portable crystallization modules that have greatly reduced the uncertainties associated with RNA crystallography. Finally, I outline unexplored avenues that can increase the impact of this technology in structural biology research and discuss potential applications of antibodies as affinity reagents for interrogating RNA biology outside of their use in crystallography. This article is categorized under: RNA Structure and Dynamics > RNA Structure, Dynamics and Chemistry RNA Interactions with Proteins and Other Molecules > Protein-RNA Recognition RNA Interactions with Proteins and Other Molecules > RNA-Protein Complexes.
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Affiliation(s)
- Saurja DasGupta
- Department of Chemistry and Biochemistry, University of Notre Dame, Notre Dame, Indiana, USA
- Department of Biological Sciences, University of Notre Dame, Notre Dame, Indiana, USA
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Hlaing ST, Srimanote P, Tongtawe P, Khantisitthiporn O, Glab-Ampai K, Chulanetra M, Thanongsaksrikul J. Isolation and Characterization of scFv Antibody against Internal Ribosomal Entry Site of Enterovirus A71. Int J Mol Sci 2023; 24:9865. [PMID: 37373012 DOI: 10.3390/ijms24129865] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/07/2023] [Revised: 06/02/2023] [Accepted: 06/06/2023] [Indexed: 06/29/2023] Open
Abstract
Enterovirus A71 (EV-A71) is one of the causative agents of hand-foot-mouth disease, which can be associated with neurocomplications of the central nervous system. A limited understanding of the virus's biology and pathogenesis has led to the unavailability of effective anti-viral treatments. The EV-A71 RNA genome carries type I internal ribosomal entry site (IRES) at 5' UTR that plays an essential role in the viral genomic translation. However, the detailed mechanism of IRES-mediated translation has not been elucidated. In this study, sequence analysis revealed that the domains IV, V, and VI of EV-A71 IRES contained the structurally conserved regions. The selected region was transcribed in vitro and labeled with biotin to use as an antigen for selecting the single-chain variable fragment (scFv) antibody from the naïve phage display library. The so-obtained scFv, namely, scFv #16-3, binds specifically to EV-A71 IRES. The molecular docking showed that the interaction between scFv #16-3 and EV-A71 IRES was mediated by the preferences of amino acid residues, including serine, tyrosine, glycine, lysine, and arginine on the antigen-binding sites contacted the nucleotides on the IRES domains IV and V. The so-produced scFv has the potential to develop as a structural biology tool to study the biology of the EV-A71 RNA genome.
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Affiliation(s)
- Su Thandar Hlaing
- Graduate Program in Biomedical Sciences, Faculty of Allied Health Sciences, Thammasat University, Pathumtani 12120, Thailand
| | - Potjanee Srimanote
- Graduate Program in Biomedical Sciences, Faculty of Allied Health Sciences, Thammasat University, Pathumtani 12120, Thailand
- Thammasat University Research Unit in Molecular Pathogenesis and Immunology of Infectious Diseases, Thammasat University, Pathumthani 12120, Thailand
| | - Pongsri Tongtawe
- Graduate Program in Biomedical Sciences, Faculty of Allied Health Sciences, Thammasat University, Pathumtani 12120, Thailand
| | - Onruedee Khantisitthiporn
- Thammasat University Research Unit in Molecular Pathogenesis and Immunology of Infectious Diseases, Thammasat University, Pathumthani 12120, Thailand
- Department of Medical Technology, Faculty of Allied Health Sciences, Thammasat University, Pathumthani 12120, Thailand
| | - Kittirat Glab-Ampai
- Center of Research Excellence in Therapeutic Proteins and Antibody Engineering, Department of Parasitology, Faculty of Medicine Siriraj Hospital, Mahidol University, Bangkok 10700, Thailand
| | - Monrat Chulanetra
- Center of Research Excellence in Therapeutic Proteins and Antibody Engineering, Department of Parasitology, Faculty of Medicine Siriraj Hospital, Mahidol University, Bangkok 10700, Thailand
| | - Jeeraphong Thanongsaksrikul
- Graduate Program in Biomedical Sciences, Faculty of Allied Health Sciences, Thammasat University, Pathumtani 12120, Thailand
- Thammasat University Research Unit in Molecular Pathogenesis and Immunology of Infectious Diseases, Thammasat University, Pathumthani 12120, Thailand
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Rees HC, Gogacz W, Li NS, Koirala D, Piccirilli JA. Structural Basis for Fluorescence Activation by Pepper RNA. ACS Chem Biol 2022; 17:1866-1875. [PMID: 35759696 PMCID: PMC9969808 DOI: 10.1021/acschembio.2c00290] [Citation(s) in RCA: 5] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Pepper is a fluorogenic RNA aptamer tag that binds to a variety of benzylidene-cyanophenyl (HBC) derivatives with tight affinity and activates their fluorescence. To investigate how Pepper RNA folds to create a binding site for HBC, we used antibody-assisted crystallography to determine the structures of Pepper bound to HBC530 and HBC599 to 2.3 and 2.7 Å resolutions, respectively. The structural data show that Pepper folds into an elongated structure and organizes nucleotides within an internal bulge to create the ligand binding site, assisted by an out-of-plane platform created by tertiary interactions with an adjacent bulge. As predicted from a lack of K+ dependence, Pepper does not use a G-quadruplex to form a binding pocket for HBC. Instead, Pepper uses a unique base-quadruple·base-triple stack to sandwich the ligand with a U·G wobble pair. Site-bound Mg2+ ions support ligand binding structurally and energetically. This research provides insight into the structural features that allow the Pepper aptamer to bind HBC and show how Pepper's function may expand to allow the in vivo detection of other small molecules and metals.
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Affiliation(s)
- Huw C. Rees
- Department of Chemistry, University of Chicago, Chicago, Illinois, 60637, United States
| | - Wojciech Gogacz
- Department of Biochemistry and Molecular Biology, University of Chicago, Chicago, Illinois, 60637, United States
| | - Nan-Sheng Li
- Department of Biochemistry and Molecular Biology, University of Chicago, Chicago, Illinois, 60637, United States
| | - Deepak Koirala
- Department of Biochemistry and Molecular Biology, University of Chicago, Chicago, Illinois, 60637, United States
| | - Joseph A. Piccirilli
- Department of Chemistry, University of Chicago, Chicago, Illinois, 60637, United States,Department of Biochemistry and Molecular Biology, University of Chicago, Chicago, Illinois, 60637, United States,corresponding author
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Krochmal D, Shao Y, Li NS, DasGupta S, Shelke SA, Koirala D, Piccirilli JA. Structural basis for substrate binding and catalysis by a self-alkylating ribozyme. Nat Chem Biol 2022; 18:376-384. [PMID: 35058645 DOI: 10.1038/s41589-021-00950-z] [Citation(s) in RCA: 8] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/14/2021] [Accepted: 11/23/2021] [Indexed: 12/26/2022]
Abstract
Ribozymes that react with small-molecule probes have important applications in transcriptomics and chemical biology, such as RNA labeling and imaging. Understanding the structural basis for these RNA-modifying reactions will enable the development of better tools for studying RNA. Nevertheless, high-resolution structures and underlying catalytic mechanisms for members of this ribozyme class remain elusive. Here, we focus on a self-alkylating ribozyme that catalyzes nitrogen-carbon bond formation between a specific guanine and a 2,3-disubstituted epoxide substrate and report the crystal structures of a self-alkylating ribozyme, including both alkylated and apo forms, at 1.71-Å and 2.49-Å resolution, respectively. The ribozyme assumes an elongated hairpin-like architecture preorganized to accommodate the epoxide substrate in a hook-shaped conformation. Observed reactivity of substrate analogs together with an inverse, log-linear pH dependence of the reaction rate suggests a requirement for epoxide protonation, possibly assisted by the ether oxygens within the substrate.
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Affiliation(s)
- Daniel Krochmal
- Department of Biochemistry and Molecular Biology, The University of Chicago, Chicago, IL, USA
| | - Yaming Shao
- Department of Biochemistry and Molecular Biology, The University of Chicago, Chicago, IL, USA
| | - Nan-Sheng Li
- Department of Biochemistry and Molecular Biology, The University of Chicago, Chicago, IL, USA
| | - Saurja DasGupta
- Department of Biochemistry and Molecular Biology, The University of Chicago, Chicago, IL, USA
| | - Sandip A Shelke
- Department of Biochemistry and Molecular Biology, The University of Chicago, Chicago, IL, USA
| | - Deepak Koirala
- Department of Chemistry and Biochemistry, University of Maryland Baltimore County, Baltimore, MD, USA.
| | - Joseph A Piccirilli
- Department of Biochemistry and Molecular Biology, The University of Chicago, Chicago, IL, USA.
- Department of Chemistry, The University of Chicago, Chicago, IL, USA.
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Davydova EK. Protein Engineering: Advances in Phage Display for Basic Science and Medical Research. BIOCHEMISTRY. BIOKHIMIIA 2022; 87:S146-S110. [PMID: 35501993 PMCID: PMC8802281 DOI: 10.1134/s0006297922140127] [Citation(s) in RCA: 5] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 08/26/2021] [Revised: 10/28/2021] [Accepted: 11/02/2021] [Indexed: 12/03/2022]
Abstract
Functional Protein Engineering became the hallmark in biomolecule manipulation in the new millennium, building on and surpassing the underlying structural DNA manipulation and recombination techniques developed and employed in the last decades of 20th century. Because of their prominence in almost all biological processes, proteins represent extremely important targets for engineering enhanced or altered properties that can lead to improvements exploitable in healthcare, medicine, research, biotechnology, and industry. Synthetic protein structures and functions can now be designed on a computer and/or evolved using molecular display or directed evolution methods in the laboratory. This review will focus on the recent trends in protein engineering and the impact of this technology on recent progress in science, cancer- and immunotherapies, with the emphasis on the current achievements in basic protein research using synthetic antibody (sABs) produced by phage display pipeline in the Kossiakoff laboratory at the University of Chicago (KossLab). Finally, engineering of the highly specific binding modules, such as variants of Streptococcal protein G with ultra-high orthogonal affinity for natural and engineered antibody scaffolds, and their possible applications as a plug-and-play platform for research and immunotherapy will be described.
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Affiliation(s)
- Elena K Davydova
- The University of Chicago, Department of Biochemistry and Molecular Biology, Chicago, IL 60637, USA.
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Affinity and Structural Analysis of the U1A RNA Recognition Motif with Engineered Methionines to Improve Experimental Phasing. CRYSTALS 2021; 11. [PMID: 33777416 PMCID: PMC7996396 DOI: 10.3390/cryst11030273] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
RNA plays a central role in all organisms and can fold into complex structures to orchestrate function. Visualization of such structures often requires crystallization, which can be a bottleneck in the structure-determination process. To promote crystallization, an RNA-recognition motif (RRM) of the U1A spliceosomal protein has been co-opted as a crystallization module. Specifically, the U1-snRNA hairpin II (hpII) single-stranded loop recognized by U1A can be transplanted into an RNA target to promote crystal contacts and to attain phase information via molecular replacement or anomalous diffraction methods using selenomethionine. Herein, we produced the F37M/F77M mutant of U1A to augment the phasing capability of this powerful crystallization module. Selenomethionine-substituted U1A(F37M/F77M) retains high affinity for hpII (K D of 59.7 ± 11.4 nM). The 2.20 Å resolution crystal structure reveals that the mutated sidechains make new S-π interactions in the hydrophobic core and are useful for single-wavelength anomalous diffraction. Crystals were also attained of U1A(F37M/F77M) in complex with a bacterial preQ1-II riboswitch. The F34M/F37M/F77M mutant was introduced similarly into a lab-evolved U1A variant (TBP6.9) that recognizes the internal bulged loop of HIV-1 TAR RNA. We envision that this short RNA sequence can be placed into non-essential duplex regions to promote crystallization and phasing of target RNAs. We show that selenomethionine-substituted TBP6.9(F34M/F37M/F77M) binds a TAR variant wherein the apical loop was replaced with a GNRA tetraloop (K D of 69.8 ± 2.9 nM), laying the groundwork for use of TBP6.9(F34M/F37M/F77M) as a crystallization module. These new tools are available to the research community.
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Chen S, Zhang W, Min J, Liu K. Lesson from a Fab-enabled co-crystallization study of TDRD2 and PIWIL1. Methods 2020; 175:72-78. [PMID: 31288074 DOI: 10.1016/j.ymeth.2019.07.002] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/28/2019] [Revised: 06/30/2019] [Accepted: 07/03/2019] [Indexed: 10/26/2022] Open
Abstract
The interaction of Tudor domain-containing proteins (TDRDs) with P-element-induced wimpy testis (PIWI) proteins plays critical roles in transposon silencing and spermatogenesis. Most human TDRDs recognize PIWI proteins in a methylarginine-dependent manner via their extended Tudor (eTudor) domains, except TDRD2, which prefers an unmethylated PIWI protein. In order to illustrate the recognition of unmethylated PIWI proteins by TDRD2, we extensively tried co-crystallization of the TDRD2 eTudor with different PIWIL1 peptides, but to no avail. Recombinant antigen-binding fragments (Fabs) have been used to crystallize some difficult proteins in the past, so we generated Fab against the TDRD2 eTudor protein using a phage-display antibody library, and one of these Fab fragments indeed facilitated the co-crystallization of TDRD2 and PIWIL1. Structural analysis of Fab, the TDRD2 eTudor domain in complex with an unmethylated PIWIL1-derived peptide revealed that the PIWIL1 residues G3 through R8 bound between the Tudor core and SN domain of TDRD2. The C-terminal residues of the PIWIL1 peptide were not resolved, presumably due to steric competition with the heavy chain of the Fab. We propose Fab-assisted crystallization as a tool not only for structural studies of single proteins, but also for analysis of interactions between proteins and their ligands in cases where co-crystallization of native protein complexes fails.
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Affiliation(s)
- Sizhuo Chen
- Hubei Key Laboratory of Genetic Regulation and Integrative Biology, School of Life Sciences, Central China Normal University, Wuhan 430079, PR China
| | - Weilian Zhang
- Structural Genomics Consortium, University of Toronto, Toronto, Ontario M5G 1L7, Canada
| | - Jinrong Min
- Hubei Key Laboratory of Genetic Regulation and Integrative Biology, School of Life Sciences, Central China Normal University, Wuhan 430079, PR China; Structural Genomics Consortium, University of Toronto, Toronto, Ontario M5G 1L7, Canada; Department of Physiology, University of Toronto, Toronto, Ontario M5S 1A8, Canada
| | - Ke Liu
- Hubei Key Laboratory of Genetic Regulation and Integrative Biology, School of Life Sciences, Central China Normal University, Wuhan 430079, PR China; Structural Genomics Consortium, University of Toronto, Toronto, Ontario M5G 1L7, Canada.
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Koirala D, Lewicka A, Koldobskaya Y, Huang H, Piccirilli JA. Synthetic Antibody Binding to a Preorganized RNA Domain of Hepatitis C Virus Internal Ribosome Entry Site Inhibits Translation. ACS Chem Biol 2020; 15:205-216. [PMID: 31765566 DOI: 10.1021/acschembio.9b00785] [Citation(s) in RCA: 14] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
Abstract
Structured RNA elements within the internal ribosome entry site (IRES) of hepatitis C virus (HCV) genome hijack host cell machinery for translation initiation through a cap-independent mechanism. Here, using a phage display selection, we obtained two antibody fragments (Fabs), HCV2 and HCV3, against HCV IRES that bind the RNA with dissociation constants of 32 ± 7 nM and 37 ± 8 nM respectively, specifically recognizing the so-called junction IIIabc (JIIIabc). We used these Fabs as crystallization chaperones and determined the high-resolution crystal structures of JIIIabc-HCV2 and -HCV3 complexes at 1.81 Å and 2.75 Å resolution respectively, revealing an antiparallel four-way junction with the IIIa and IIIc subdomains brought together through tertiary interactions. The RNA conformation observed in the structures supports the structural model for this region derived from cryo-EM data for the HCV IRES-40S ribosome complex, suggesting that the tertiary fold of the RNA preorganizes the domain for interactions with the 40S ribosome. Strikingly, both Fabs and the ribosomal protein eS27 not only interact with a common subset of nucleotides within the JIIIabc but also use physiochemically similar sets of protein residues to do so, suggesting that the RNA surface is well-suited for interactions with proteins, perhaps analogous to the "hot spot" concept elaborated for protein-protein interactions. Using a rabbit reticulocyte lysate-based translation assay with a bicistronic reporter construct, we further demonstrated that Fabs HCV2 and HCV3 specifically inhibit the HCV IRES-directed translation, implicating disruption of the JIIIabc-ribosome interaction as a potential therapeutic strategy against HCV.
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Affiliation(s)
- Deepak Koirala
- Department of Biochemistry and Molecular Biology, The University of Chicago, Chicago, Illinois 60637, United States
| | - Anna Lewicka
- Department of Biochemistry and Molecular Biology, The University of Chicago, Chicago, Illinois 60637, United States
| | - Yelena Koldobskaya
- Department of Biochemistry and Molecular Biology, The University of Chicago, Chicago, Illinois 60637, United States
| | - Hao Huang
- Department of Biochemistry and Molecular Biology, The University of Chicago, Chicago, Illinois 60637, United States
| | - Joseph A. Piccirilli
- Department of Biochemistry and Molecular Biology, The University of Chicago, Chicago, Illinois 60637, United States
- Department of Chemistry, The University of Chicago, Chicago, Illinois 60637, United States
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Koirala D, Shao Y, Koldobskaya Y, Fuller JR, Watkins AM, Shelke SA, Pilipenko EV, Das R, Rice PA, Piccirilli JA. A conserved RNA structural motif for organizing topology within picornaviral internal ribosome entry sites. Nat Commun 2019; 10:3629. [PMID: 31399592 PMCID: PMC6689051 DOI: 10.1038/s41467-019-11585-z] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/17/2018] [Accepted: 07/09/2019] [Indexed: 12/30/2022] Open
Abstract
Picornaviral IRES elements are essential for initiating the cap-independent viral translation. However, three-dimensional structures of these elements remain elusive. Here, we report a 2.84-Å resolution crystal structure of hepatitis A virus IRES domain V (dV) in complex with a synthetic antibody fragment-a crystallization chaperone. The RNA adopts a three-way junction structure, topologically organized by an adenine-rich stem-loop motif. Despite no obvious sequence homology, the dV architecture shows a striking similarity to a circularly permuted form of encephalomyocarditis virus J-K domain, suggesting a conserved strategy for organizing the domain architecture. Recurrence of the motif led us to use homology modeling tools to compute a 3-dimensional structure of the corresponding domain of foot-and-mouth disease virus, revealing an analogous domain organizing motif. The topological conservation observed among these IRESs and other viral domains implicates a structured three-way junction as an architectural scaffold to pre-organize helical domains for recruiting the translation initiation machinery.
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Affiliation(s)
- Deepak Koirala
- Department of Biochemistry and Molecular Biology, The University of Chicago, Chicago, IL, 60637, USA
| | - Yaming Shao
- Department of Biochemistry and Molecular Biology, The University of Chicago, Chicago, IL, 60637, USA
| | - Yelena Koldobskaya
- Department of Biochemistry and Molecular Biology, The University of Chicago, Chicago, IL, 60637, USA
| | - James R Fuller
- Department of Biochemistry and Molecular Biology, The University of Chicago, Chicago, IL, 60637, USA
| | - Andrew M Watkins
- Department of Biochemistry, Stanford University School of Medicine, Stanford, CA, 94305, USA
| | - Sandip A Shelke
- Department of Biochemistry and Molecular Biology, The University of Chicago, Chicago, IL, 60637, USA
| | - Evgeny V Pilipenko
- Department of Biochemistry and Molecular Biology, The University of Chicago, Chicago, IL, 60637, USA
| | - Rhiju Das
- Department of Biochemistry, Stanford University School of Medicine, Stanford, CA, 94305, USA
| | - Phoebe A Rice
- Department of Biochemistry and Molecular Biology, The University of Chicago, Chicago, IL, 60637, USA
| | - Joseph A Piccirilli
- Department of Biochemistry and Molecular Biology, The University of Chicago, Chicago, IL, 60637, USA.
- Department of Chemistry, The University of Chicago, Chicago, IL, 60637, USA.
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Cawez F, Duray E, Hu Y, Vandenameele J, Romão E, Vincke C, Dumoulin M, Galleni M, Muyldermans S, Vandevenne M. Combinatorial Design of a Nanobody that Specifically Targets Structured RNAs. J Mol Biol 2018; 430:1652-1670. [PMID: 29654796 DOI: 10.1016/j.jmb.2018.03.032] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/12/2018] [Revised: 03/08/2018] [Accepted: 03/27/2018] [Indexed: 10/17/2022]
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Koirala D, Shelke SA, Dupont M, Ruiz S, DasGupta S, Bailey LJ, Benner SA, Piccirilli JA. Affinity maturation of a portable Fab-RNA module for chaperone-assisted RNA crystallography. Nucleic Acids Res 2018; 46:2624-2635. [PMID: 29309709 PMCID: PMC5861428 DOI: 10.1093/nar/gkx1292] [Citation(s) in RCA: 23] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/26/2017] [Revised: 12/13/2017] [Accepted: 12/28/2017] [Indexed: 12/13/2022] Open
Abstract
Antibody fragments such as Fabs possess properties that can enhance protein and RNA crystallization and therefore can facilitate macromolecular structure determination. In particular, Fab BL3-6 binds to an AAACA RNA pentaloop closed by a GC pair with ∼100 nM affinity. The Fab and hairpin have served as a portable module for RNA crystallization. The potential for general application make it desirable to adjust the properties of this crystallization module in a manner that facilitates its use for RNA structure determination, such as ease of purification, surface entropy or binding affinity. In this work, we used both in vitro RNA selection and phage display selection to alter the epitope and paratope sides of the binding interface, respectively, for improved binding affinity. We identified a 5'-GNGACCC-3' consensus motif in the RNA and S97N mutation in complimentarity determining region L3 of the Fab that independently impart about an order of magnitude improvement in affinity, resulting from new hydrogen bonding interactions. Using a model RNA, these modifications facilitated crystallization under a wider range of conditions and improved diffraction. The improved features of the Fab-RNA module may facilitate its use as an affinity tag for RNA purification and imaging and as a chaperone for RNA crystallography.
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Affiliation(s)
- Deepak Koirala
- Department of Biochemistry and Molecular Biology, The University of Chicago, Chicago, IL 60637, USA
| | - Sandip A Shelke
- Department of Biochemistry and Molecular Biology, The University of Chicago, Chicago, IL 60637, USA
| | - Marcel Dupont
- Department of Biochemistry and Molecular Biology, The University of Chicago, Chicago, IL 60637, USA
| | - Stormy Ruiz
- Department of Chemistry, The University of Chicago, Chicago, IL 60637, USA
| | - Saurja DasGupta
- Department of Chemistry, The University of Chicago, Chicago, IL 60637, USA
| | - Lucas J Bailey
- Department of Biochemistry and Molecular Biology, The University of Chicago, Chicago, IL 60637, USA
| | - Steven A Benner
- Foundation for Applied Molecular Evolution, Firebird Biomolecular Sciences LLC, 13709 Progress Boulevard, Alachua, FL 32615, USA
| | - Joseph A Piccirilli
- Department of Biochemistry and Molecular Biology, The University of Chicago, Chicago, IL 60637, USA
- Department of Chemistry, The University of Chicago, Chicago, IL 60637, USA
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