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Roy Chowdhury S, Khdour OM, Bandyopadhyay I, Hecht SM. Lipophilic methylene violet analogues as modulators of mitochondrial function and dysfunction. Bioorg Med Chem 2017; 25:5537-5547. [PMID: 28927904 DOI: 10.1016/j.bmc.2017.08.021] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/24/2017] [Revised: 08/08/2017] [Accepted: 08/10/2017] [Indexed: 11/16/2022]
Abstract
In an effort to identify methylene blue analogues having improved antioxidant activity, a series of new methylene violet analogues have been designed and synthesized. The analogues were prepared following a synthetic route that is more efficient than the previously reported methods, both in terms of yield and purity of the final products. The route involves the Smiles rearrangement as one of the crucial steps. Smiles rearrangement of suitably substituted diphenyl sulfide intermediates afforded the corresponding phenothiazine analogues in high yields, which were subsequently converted to the final products. The methylene violet analogues were evaluated for their ability to preserve mitochondrial function in Friedreich's ataxia (FRDA) lymphocytes. The analogues were shown to be efficient ROS scavengers, and able to protect cultured FRDA lymphocytes from oxidative stress resulting from inhibition of complex I. The analogues also preserved mitochondrial membrane potential and augmented ATP production. The analogues were found to be better antioxidants than the parent compounds methylene blue and methylene violet.
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Arutla V, Leal J, Liu X, Sokalingam S, Raleigh M, Adaralegbe A, Liu L, Pentel PR, Hecht SM, Chang Y. Prescreening of Nicotine Hapten Linkers in Vitro To Select Hapten-Conjugate Vaccine Candidates for Pharmacokinetic Evaluation in Vivo. ACS COMBINATORIAL SCIENCE 2017; 19:286-298. [PMID: 28383252 PMCID: PMC5916772 DOI: 10.1021/acscombsci.6b00179] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
Abstract
Since the demonstration of nicotine vaccines as a possible therapeutic intervention for the effects of tobacco smoke, extensive effort has been made to enhance nicotine specific immunity. Linker modifications of nicotine haptens have been a focal point for improving the immunogenicity of nicotine, in which the evaluation of these modifications usually relies on in vivo animal models, such as mice, rats or nonhuman primates. Here, we present two in vitro screening strategies to estimate and predict the immunogenic potential of our newly designed nicotine haptens. One utilizes a competition enzyme-linked immunoabsorbent assay (ELISA) to profile the interactions of nicotine haptens or hapten-protein conjugates with nicotine specific antibodies, both polyclonal and monoclonal. Another relies on computational modeling of the interactions between haptens and amino acid residues near the conjugation site of the carrier protein to infer linker-carrier protein conjugation effect on antinicotine antibody response. Using these two in vitro methods, we ranked the haptens with different linkers for their potential as viable vaccine candidates. The ELISA-based hapten ranking was in an agreement with the results obtained by in vivo nicotine pharmacokinetic analysis. A correlation was found between the average binding affinity (IC50) of the haptens to an anti-Nic monoclonal antibody and the average brain nicotine concentration in the immunized mice. The computational modeling of hapten and carrier protein interactions helps exclude conjugates with strong linker-carrier conjugation effects and low in vivo efficacy. The simplicity of these in vitro screening strategies should facilitate the selection and development of more effective nicotine conjugate vaccines. In addition, these data highlight a previously under-appreciated contribution of linkers and hapten-protein conjugations to conjugate vaccine immunogenicity by virtue of their inclusion in the epitope that binds and activates B cells.
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Bai X, Talukder P, Daskalova SM, Roy B, Chen S, Li Z, Dedkova LM, Hecht SM. Enhanced Binding Affinity for an i-Motif DNA Substrate Exhibited by a Protein Containing Nucleobase Amino Acids. J Am Chem Soc 2017; 139:4611-4614. [PMID: 28263595 DOI: 10.1021/jacs.6b11825] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
Several variants of a nucleic acid binding motif (RRM1) of putative transcription factor hnRNP LL containing nucleobase amino acids at specific positions have been prepared and used to study binding affinity for the BCL2 i-motif DNA. Molecular modeling suggested a number of amino acids in RRM1 likely to be involved in interaction with the i-motif DNA, and His24 and Arg26 were chosen for modification based on their potential ability to interact with G14 of the i-motif DNA. Four nucleobase amino acids were introduced into RRM1 at one or both of positions 24 and 26. The introduction of cytosine nucleobase 2 into position 24 of RRM1 increased the affinity of the modified protein for the i-motif DNA, consistent with the possible Watson-Crick interaction of 2 and G14. In comparison, the introduction of uracil nucleobase 3 had a minimal effect on DNA affinity. Two structurally simplified nucleobase analogues (1 and 4) lacking both the N-1 and the 2-oxo substituents were also introduced in lieu of His24. Again, the RRM1 analogue containing 1 exhibited enhanced affinity for the i-motif DNA, while the protein analogue containing 4 bound less tightly to the DNA substrate. Finally, the modified protein containing 1 in lieu of Arg26 also bound to the i-motif DNA more strongly than the wild-type protein, but a protein containing 1 both at positions 24 and 26 bound to the DNA less strongly than wild type. The results support the idea of using nucleobase amino acids as protein constituents for controlling and enhancing DNA-protein interaction. Finally, modification of the i-motif DNA at G14 diminished RRM1-DNA interaction, as well as the ability of nucleobase amino acid 1 to stabilize RRM1-DNA interaction.
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Daskalova SM, Bhattacharya C, Dedkova LM, Hecht SM. Probing the Flexibility of the Catalytic Nucleophile in the Lyase Catalytic Pocket of Human DNA Polymerase β with Unnatural Lysine Analogues. Biochemistry 2017; 56:500-513. [PMID: 28005340 DOI: 10.1021/acs.biochem.6b00807] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/23/2023]
Abstract
DNA polymerase β (Pol β) is a key enzyme in mammalian base excision repair (BER), contributing stepwise 5'-deoxyribose phosphate (dRP) lyase and "gap-filling" DNA polymerase activities. The lyase reaction is believed to occur via a β-elimination reaction following the formation of a Schiff base between the dRP group at the pre-incised apurinic/apyrimidinic site and the ε-amino group of Lys72. To probe the steric constraints on the formation and subsequent resolution of the putative Schiff base intermediate within the lyase catalytic pocket, Lys72 was replaced with each of several nonproteinogenic lysine analogues. The modified Pol β enzymes were produced by coupled in vitro transcription and translation from a modified DNA template containing a TAG codon at the position corresponding to Lys72. In the presence of a misacylated tRNACUA transcript, suppression of the UAG codon in the transcribed mRNA led to elaboration of full length Pol β having a lysine analogue at position 72. Replacement of the primary nucleophilic amine with a secondary amine in the form of N-methyllysine (4) affected mainly the stability of the Schiff base intermediate and resulted in relatively moderate inhibition of lyase activity and BER. Elongation of the side chain of the catalytic residue by one methylene group, achieved by introduction of homolysine (6) at position 72, apparently shifted the amino group to a position less favorable for Schiff base formation. Interestingly, this effect was attenuated when the side chain was elongated by replacing one side-chain methylene group with a bridging S atom (thialysine, 2). In comparison, replacement of lysine 72 with an analogue having a guanidine moiety in lieu of an ε-amino group (homoarginine, 5) or a sterically constrained secondary amine (piperidinylalanine, 3) led to almost complete suppression of dRP excision activity and the ability of Pol β to support BER. These results help to define the tolerance of Pol β to subtle local structural and functional alterations.
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Chevalier A, Khdour OM, Schmierer M, Bandyopadhyay I, Hecht SM. Influence of substituent heteroatoms on the cytoprotective properties of pyrimidinol antioxidants. Bioorg Med Chem 2017; 25:1703-1716. [PMID: 28189395 DOI: 10.1016/j.bmc.2017.01.030] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/06/2016] [Revised: 01/18/2017] [Accepted: 01/21/2017] [Indexed: 01/04/2023]
Abstract
Recently, we described the optimization of novel pyrimidinol-based antioxidants as potential therapeutic molecules for targeting mitochondrial diseases. That study focused on improving the potency and metabolic stability of pyrimidinol antioxidants. This led us to consider the possibility of altering the positions of the exocyclic alkoxy and alkylamino substituents on the pyrimidinol scaffold. Twelve new analogues were prepared and their biological activities were investigated. The metabolic stability of the prepared regioisomers was also assessed in vitro using bovine liver microsomes. Unexpectedly, the 2-alkoxy-4-alkylamino substituted pyrimidinol antioxidants were found to have properties in protecting mitochondrial function superior to the isomeric 4-alkoxy-2-alkylamino substituted pyrimidinols evaluated in all earlier studies. This observation suggests a possible mode of action involving the intermediacy of an ortho-iminoquinone, a species not previously associated with mitochondrial respiratory chain function.
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Zhang Y, Jiang S, Zhang D, Bai X, Hecht SM, Chen S. DNA–affibody nanoparticles for inhibiting breast cancer cells overexpressing HER2. Chem Commun (Camb) 2017; 53:573-576. [DOI: 10.1039/c6cc08495h] [Citation(s) in RCA: 30] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
A DNA tetrahedron–affibody–drug nanoparticle is a highly efficient tool to deliver doxorubicin (DOX) to HER2 overexpressing cancer cells specifically. It represents a highly efficacious agent for selectively inhibiting cancer cells which overexpress HER2 receptor.
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Chevalier A, Zhang Y, Khdour OM, Kaye JB, Hecht SM. Mitochondrial Nitroreductase Activity Enables Selective Imaging and Therapeutic Targeting. J Am Chem Soc 2016; 138:12009-12. [PMID: 27571326 DOI: 10.1021/jacs.6b06229] [Citation(s) in RCA: 113] [Impact Index Per Article: 14.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
Nitroreductase (NTR) activities have been known for decades, studied extensively in bacteria and also in systems as diverse as yeast, trypanosomes, and hypoxic tumors. The putative bacterial origin of mitochondria prompted us to explore the possible existence of NTR activity within this organelle and to probe its behavior in a cellular context. Presently, by using a profluorescent near-infrared (NIR) dye, we characterize the nature of NTR activity localized in mammalian cell mitochondria. Further, we demonstrate that this mitochondrially localized enzymatic activity can be exploited both for selective NIR imaging of mitochondria and for mitochondrial targeting by activating a mitochondrial poison specifically within that organelle. This constitutes a new mechanism for mitochondrial imaging and targeting. These findings represent the first use of mitochondrial enzyme activity to unmask agents for mitochondrial fluorescent imaging and therapy, which may prove to be more broadly applicable.
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Kendrick S, Kang HJ, Alam MP, Madathil MM, Agrawal P, Gokhale V, Yang D, Hecht SM, Hurley LH. Correction to "The Dynamic Character of the BCL2 Promoter i-Motif Provides a Mechanism for Modulation of Gene Expression by Compounds That Bind Selectively to the Alternative DNA Hairpin Structure". J Am Chem Soc 2016; 138:11408. [PMID: 27571358 PMCID: PMC8154439 DOI: 10.1021/jacs.6b07292] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
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Chevalier A, Alam MP, Khdour OM, Schmierer M, Arce PM, Cripe CD, Hecht SM. Optimization of pyrimidinol antioxidants as mitochondrial protective agents: ATP production and metabolic stability. Bioorg Med Chem 2016; 24:5206-5220. [PMID: 27624526 DOI: 10.1016/j.bmc.2016.08.039] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/15/2016] [Revised: 08/17/2016] [Accepted: 08/22/2016] [Indexed: 12/19/2022]
Abstract
Previously we described a novel series of pyrimidinol antioxidants and their structural optimization as potential therapeutic agents for neurodegenerative and mitochondrial disorders. Our initial lead compound was a potent antioxidant in vitro, but was subsequently found to exhibit poor stability to oxidative metabolism. The current study focused on balancing potency with metabolic stability through structural modification, and involved modifications at positions 2 and 4 of the pyrimidinol redox core, likely sites of oxidative metabolism. Eight new analogues have been prepared and their ability to suppress lipid peroxidation and reactive oxygen species (ROS), and to preserve mitochondrial membrane potential (Δψm) and support ATP production, has been investigated. The metabolic stability of the prepared compounds was also assessed in vitro using bovine liver microsomes to obtain preliminary insight on this class of compounds. This study revealed the complexity of balancing reasonable metabolic stability with efficient antioxidant properties. While a few analogues appear promising, especially in terms of metabolic stability, a 4-isopropoxy derivative conserved the favorable biological activity and exhibited good metabolic stability. The favorable metabolic stability conferred by the combination of the azetidine and isopropoxy moieties in analogue 6 makes this compound an excellent candidate for further evaluation.
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Roy B, Talukder P, Kang HJ, Tsuen SS, Alam MP, Hurley LH, Hecht SM. Interaction of Individual Structural Domains of hnRNP LL with the BCL2 Promoter i-Motif DNA. J Am Chem Soc 2016; 138:10950-62. [DOI: 10.1021/jacs.6b05036] [Citation(s) in RCA: 32] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/08/2023]
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36
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Talukder P, Dedkova LM, Ellington AD, Yakovchuk P, Lim J, Anslyn EV, Hecht SM. Synthesis of alanyl nucleobase amino acids and their incorporation into proteins. Bioorg Med Chem 2016; 24:4177-4187. [PMID: 27452282 DOI: 10.1016/j.bmc.2016.07.008] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/25/2016] [Revised: 07/02/2016] [Accepted: 07/05/2016] [Indexed: 01/13/2023]
Abstract
Proteins which bind to nucleic acids and regulate their structure and functions are numerous and exceptionally important. Such proteins employ a variety of strategies for recognition of the relevant structural elements in their nucleic acid substrates, some of which have been shown to involve rather subtle interactions which might have been difficult to design from first principles. In the present study, we have explored the preparation of proteins containing unnatural amino acids having nucleobase side chains. In principle, the introduction of multiple nucleobase amino acids into the nucleic acid binding domain of a protein should enable these modified proteins to interact with their nucleic acid substrates using Watson-Crick and other base pairing interactions. We describe the synthesis of five alanyl nucleobase amino acids protected in a fashion which enabled their attachment to a suppressor tRNA, and their incorporation into each of two proteins with acceptable efficiencies. The nucleobases studied included cytosine, uracil, thymine, adenine and guanine, i.e. the major nucleobase constituents of DNA and RNA. Dihydrofolate reductase was chosen as one model protein to enable direct comparison of the facility of incorporation of the nucleobase amino acids with numerous other unnatural amino acids studied previously. The Klenow fragment of DNA polymerase I was chosen as a representative DNA binding protein whose mode of action has been studied in detail.
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Chevalier A, Zhang Y, Khdour OM, Hecht SM. Selective Functionalization of Antimycin A Through an N-Transacylation Reaction. Org Lett 2016; 18:2395-8. [DOI: 10.1021/acs.orglett.6b00882] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
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Chowdhury SR, Chauhan PS, Dedkova LM, Bai X, Chen S, Talukder P, Hecht SM. Synthesis and Evaluation of a Library of Fluorescent Dipeptidomimetic Analogues as Substrates for Modified Bacterial Ribosomes. Biochemistry 2016; 55:2427-40. [PMID: 27050631 DOI: 10.1021/acs.biochem.6b00102] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Described herein are the synthesis and photophysical characterization of a library of aryl-substituted oxazole- and thiazole-based dipeptidomimetic analogues, and their incorporation into position 66 of green fluorescent protein (GFP) in lieu of the natural fluorophore. These fluorescent analogues resemble the fluorophore formed naturally by GFP. As anticipated, the photophysical properties of the analogues varied as a function of the substituents at the para position of the phenyl ring. The fluorescence emission wavelength maxima of compounds in the library varied from ∼365 nm (near-UV region) to ∼490 nm (visible region). The compounds also exhibited a large range of quantum yields (0.01-0.92). The analogues were used to activate a suppressor tRNACUA and were incorporated into position 66 of GFP using an in vitro protein biosynthesizing system that employed engineered ribosomes selected for their ability to incorporate dipeptides. Four analogues with interesting photophysical properties and reasonable suppression yields were chosen, and the fluorescent proteins (FPs) containing these fluorophores were prepared on a larger scale for more detailed study. When the FPs were compared with the respective aminoacyl-tRNAs and the actual dipeptide analogues, the FPs exhibited significantly enhanced fluorescence intensities at the same concentrations. Part of this was shown to be due to the presence of the fluorophores as an intrinsic element of the protein backbone. There were also characteristic shifts in the emission maxima, indicating the environmental sensitivity of these probes. Acridon-2-ylalanine and oxazole 1a were incorporated into positions 39 and 66 of GFP, respectively, and were shown to form an efficient Förster resonance energy transfer (FRET) pair, demonstrating that the analogues can be used as FRET probes.
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Talukder P, Chen S, Roy B, Yakovchuk P, Spiering MM, Alam MP, Madathil MM, Bhattacharya C, Benkovic SJ, Hecht SM. Cyanotryptophans as Novel Fluorescent Probes for Studying Protein Conformational Changes and DNA–Protein Interaction. Biochemistry 2015; 54:7457-69. [DOI: 10.1021/acs.biochem.5b01085] [Citation(s) in RCA: 49] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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Gerasimova YV, Yakovchuk P, Dedkova LM, Hecht SM, Kolpashchikov DM. Expedited quantification of mutant ribosomal RNA by binary deoxyribozyme (BiDz) sensors. RNA (NEW YORK, N.Y.) 2015; 21:1834-43. [PMID: 26289345 PMCID: PMC4574759 DOI: 10.1261/rna.052613.115] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/21/2015] [Accepted: 07/13/2015] [Indexed: 05/06/2023]
Abstract
Mutations in ribosomal RNA (rRNA) have traditionally been detected by the primer extension assay, which is a tedious and multistage procedure. Here, we describe a simple and straightforward fluorescence assay based on binary deoxyribozyme (BiDz) sensors. The assay uses two short DNA oligonucleotides that hybridize specifically to adjacent fragments of rRNA, one of which contains a mutation site. This hybridization results in the formation of a deoxyribozyme catalytic core that produces the fluorescent signal and amplifies it due to multiple rounds of catalytic action. This assay enables us to expedite semi-quantification of mutant rRNA content in cell cultures starting from whole cells, which provides information useful for optimization of culture preparation prior to ribosome isolation. The method requires less than a microliter of a standard Escherichia coli cell culture and decreases analysis time from several days (for primer extension assay) to 1.5 h with hands-on time of ∼10 min. It is sensitive to single-nucleotide mutations. The new assay simplifies the preliminary analysis of RNA samples and cells in molecular biology and cloning experiments and is promising in other applications where fast detection/quantification of specific RNA is required.
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Maini R, Dedkova LM, Paul R, Madathil MM, Chowdhury SR, Chen S, Hecht SM. Ribosome-Mediated Incorporation of Dipeptides and Dipeptide Analogues into Proteins in Vitro. J Am Chem Soc 2015; 137:11206-9. [PMID: 26301427 DOI: 10.1021/jacs.5b03135] [Citation(s) in RCA: 48] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/11/2023]
Abstract
Plasmids containing 23S rRNA randomized at positions 2057-2063 and 2502-2507 were introduced into Escherichia coli, affording a library of clones which produced modified ribosomes in addition to the pre-existing wild-type ribosomes. These clones were screened with a derivative of puromycin, a natural product which acts as an analogue of the 3'-end of aminoacyl-tRNA and terminates protein synthesis by accepting the growing polypeptide chain, thereby killing bacterial cells. The puromycin derivative in this study contained the dipeptide p-methoxyphenylalanylglycine, implying the ability of the modified ribosomes in clones sensitive to this puromycin analogue to recognize dipeptides. Several clones inhibited by the puromycin derivative were used to make S-30 preparations, and some of these were shown to support the incorporation of dipeptides into proteins. The four incorporated species included two dipeptides (Gly-Phe (2) and Phe-Gly (3)), as well as a thiolated dipeptide analogue (4) and a fluorescent oxazole (5) having amine and carboxyl groups approximately the same distance apart as in a normal dipeptide. A protein containing both thiolated dipeptide 4 and a 7-methoxycoumarin fluorophore was found to undergo fluorescence quenching. Introduction of the oxazole fluorophore 5 into dihydrofolate reductase or green fluorescent protein resulted in quite strong enhancement of its fluorescence emission, and the basis for this enhancement was studied. The aggregate results demonstrate the feasibility of incorporating dipeptides as a single ribosomal event, and illustrate the lack of recognition of the central peptide bond in the dipeptide, potentially enabling the incorporation of a broad variety of structural analogues.
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Maini R, Chowdhury SR, Dedkova LM, Roy B, Daskalova SM, Paul R, Chen S, Hecht SM. Protein Synthesis with Ribosomes Selected for the Incorporation of β-Amino Acids. Biochemistry 2015; 54:3694-706. [PMID: 25982410 PMCID: PMC4472090 DOI: 10.1021/acs.biochem.5b00389] [Citation(s) in RCA: 53] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/13/2015] [Revised: 05/16/2015] [Indexed: 02/04/2023]
Abstract
In an earlier study, β³-puromycin was used for the selection of modified ribosomes, which were utilized for the incorporation of five different β-amino acids into Escherichia coli dihydrofolate reductase (DHFR). The selected ribosomes were able to incorporate structurally disparate β-amino acids into DHFR, in spite of the use of a single puromycin for the selection of the individual clones. In this study, we examine the extent to which the structure of the β³-puromycin employed for ribosome selection influences the regio- and stereochemical preferences of the modified ribosomes during protein synthesis; the mechanistic probe was a single suppressor tRNA(CUA) activated with each of four methyl-β-alanine isomers (1-4). The modified ribosomes were found to incorporate each of the four isomeric methyl-β-alanines into DHFR but exhibited a preference for incorporation of 3(S)-methyl-β-alanine (β-mAla; 4), i.e., the isomer having the same regio- and stereochemistry as the O-methylated β-tyrosine moiety of β³-puromycin. Also conducted were a selection of clones that are responsive to β²-puromycin and a demonstration of reversal of the regio- and stereochemical preferences of these clones during protein synthesis. These results were incorporated into a structural model of the modified regions of 23S rRNA, which included in silico prediction of a H-bonding network. Finally, it was demonstrated that incorporation of 3(S)-methyl-β-alanine (β-mAla; 4) into a short α-helical region of the nucleic acid binding domain of hnRNP LL significantly stabilized the helix without affecting its DNA binding properties.
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MESH Headings
- Alanine/analogs & derivatives
- Alanine/chemistry
- Alanine/metabolism
- Escherichia coli/enzymology
- Escherichia coli/metabolism
- Escherichia coli Proteins/biosynthesis
- Escherichia coli Proteins/chemistry
- Heterogeneous-Nuclear Ribonucleoprotein L/biosynthesis
- Heterogeneous-Nuclear Ribonucleoprotein L/chemistry
- Heterogeneous-Nuclear Ribonucleoprotein L/genetics
- Humans
- Hydrogen Bonding
- Models, Molecular
- Molecular Dynamics Simulation
- Mutant Proteins/biosynthesis
- Mutant Proteins/chemistry
- Mutant Proteins/genetics
- Nucleotide Motifs
- Peptidyl Transferases/genetics
- Peptidyl Transferases/metabolism
- Protein Conformation
- Protein Stability
- Puromycin/analogs & derivatives
- Puromycin/chemistry
- Puromycin/metabolism
- RNA, Bacterial/chemistry
- RNA, Bacterial/metabolism
- RNA, Ribosomal/chemistry
- RNA, Ribosomal/metabolism
- RNA, Ribosomal, 23S/chemistry
- RNA, Ribosomal, 23S/metabolism
- RNA, Transfer, Amino Acyl/chemistry
- RNA, Transfer, Amino Acyl/metabolism
- Recombinant Proteins/biosynthesis
- Recombinant Proteins/chemistry
- Ribosomes/metabolism
- Stereoisomerism
- Substrate Specificity
- Tetrahydrofolate Dehydrogenase/biosynthesis
- Tetrahydrofolate Dehydrogenase/chemistry
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Yu Z, Paul R, Bhattacharya C, Bozeman TC, Rishel MJ, Hecht SM. Structural features facilitating tumor cell targeting and internalization by bleomycin and its disaccharide. Biochemistry 2015; 54:3100-9. [PMID: 25905565 PMCID: PMC4440614 DOI: 10.1021/acs.biochem.5b00277] [Citation(s) in RCA: 34] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
We have shown previously that the bleomycin (BLM) carbohydrate moiety can recapitulate the tumor cell targeting effects of the entire BLM molecule, that BLM itself is modular in nature consisting of a DNA-cleaving aglycone which is delivered selectively to the interior of tumor cells by its carbohydrate moiety, and that there are disaccharides structurally related to the BLM disaccharide which are more efficient than the natural disaccharide at tumor cell targeting/uptake. Because BLM sugars can deliver molecular cargoes selectively to tumor cells, and thus potentially form the basis for a novel antitumor strategy, it seemed important to consider additional structural features capable of affecting the efficiency of tumor cell recognition and delivery. These included the effects of sugar polyvalency and net charge (at physiological pH) on tumor cell recognition, internalization, and trafficking. Since these parameters have been shown to affect cell surface recognition, internalization, and distribution in other contexts, this study has sought to define the effects of these structural features on tumor cell recognition by bleomycin and its disaccharide. We demonstrate that both can have a significant effect on tumor cell binding/internalization, and present data which suggests that the metal ions normally bound by bleomycin following clinical administration may significantly contribute to the efficiency of tumor cell uptake, in addition to their characterized function in DNA cleavage. A BLM disaccharide-Cy5** conjugate incorporating the positively charged dipeptide d-Lys-d-Lys was found to associate with both the mitochondria and the nuclear envelope of DU145 cells, suggesting possible cellular targets for BLM disaccharide-cytotoxin conjugates.
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Mastroeni D, Khdour OM, Arce PM, Hecht SM, Coleman PD. Novel antioxidants protect mitochondria from the effects of oligomeric amyloid beta and contribute to the maintenance of epigenome function. ACS Chem Neurosci 2015; 6:588-98. [PMID: 25668062 DOI: 10.1021/cn500323q] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023] Open
Abstract
Alzheimer's disease is associated with metabolic deficits and reduced mitochondrial function, with the latter due to the effects of oligomeric amyloid beta peptide (AβO) on the respiratory chain. Recent evidence has demonstrated reduction of epigenetic markers, such as DNA methylation, in Alzheimer's disease. Here we demonstrate a link between metabolic and epigenetic deficits via reduction of mitochondrial function which alters the expression of mediators of epigenetic modifications. AβO-induced loss of mitochondrial function in differentiated neuronal cells was reversed using two novel antioxidants (1 and 2); both have been shown to mitigate the effects of reactive oxygen species (ROS), and compound 1 also restores adenosine triphosphate (ATP) levels. While both compounds were effective in reducing ROS, restoration of ATP levels was associated with a more robust response to AβO treatment. Our in vitro system recapitulates key aspects of data from Alzheimer's brain samples, the expression of epigenetic genes in which are also shown to be normalized by the novel analogues.
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Talukder P, Chen S, Liu CT, Baldwin EA, Benkovic SJ, Hecht SM. Tryptophan-based fluorophores for studying protein conformational changes. Bioorg Med Chem 2014; 22:5924-34. [PMID: 25284250 PMCID: PMC4254292 DOI: 10.1016/j.bmc.2014.09.015] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/21/2014] [Revised: 09/03/2014] [Accepted: 09/08/2014] [Indexed: 11/19/2022]
Abstract
With the continuing interest in deciphering the interplay between protein function and conformational changes, small fluorescence probes will be especially useful for tracking changes in the crowded protein interior space. Presently, we describe the potential utility of six unnatural amino acid fluorescence donors structurally related to tryptophan and show how they can be efficiently incorporated into a protein as fluorescence probes. We also examine the various photophysical properties of the new Trp analogues, which are significantly redshifted in their fluorescence spectra relative to tryptophan. In general, the Trp analogues were well tolerated when inserted into Escherichia coli DHFR, and did not perturb enzyme activity, although substitution for Trp22 did result in a diminution in DHFR activity. Further, it was demonstrated that D and E at position 37 formed efficient FRET pairs with acridon-2-ylalanine (Acd) at position 17. The same was also true for a DHFR construct containing E at position 79 and Acd at position 17. Together, these findings demonstrate that these tryptophan analogues can be introduced into DHFR with minimal disruption of function, and that they can be employed for the selective study of targeted conformational changes in proteins, even in the presence of unmodified tryptophans.
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Bernatchez JA, Paul R, Tchesnokov EP, Ngure M, Beilhartz GL, Berghuis AM, Lavoie R, Li L, Auger A, Melnyk RA, Grobler JA, Miller MD, Hazuda DJ, Hecht SM, Götte M. Derivatives of mesoxalic acid block translocation of HIV-1 reverse transcriptase. J Biol Chem 2014; 290:1474-84. [PMID: 25355312 DOI: 10.1074/jbc.m114.614305] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The pyrophosphate mimic and broad spectrum antiviral phosphonoformic acid (PFA, foscarnet) was shown to freeze the pre-translocational state of the reverse transcriptase (RT) complex of the human immunodeficiency virus type 1 (HIV-1). However, PFA lacks a specificity domain, which is seen as a major reason for toxic side effects associated with the clinical use of this drug. Here, we studied the mechanism of inhibition of HIV-1 RT by the 4-chlorophenylhydrazone of mesoxalic acid (CPHM) and demonstrate that this compound also blocks RT translocation. Hot spots for inhibition with PFA or CPHM occur at template positions with a bias toward pre-translocation. Mutations at active site residue Asp-185 compromise binding of both compounds. Moreover, divalent metal ions are required for the formation of ternary complexes with either of the two compounds. However, CPHM contains both an anchor domain that likely interacts with the catalytic metal ions and a specificity domain. Thus, although the inhibitor binding sites may partly overlap, they are not identical. The K65R mutation in HIV-1 RT, which reduces affinity to PFA, increases affinity to CPHM. Details with respect to the binding sites of the two inhibitors are provided on the basis of mutagenesis studies, structure-activity relationship analyses with newly designed CPHM derivatives, and in silico docking experiments. Together, these findings validate the pre-translocated complex of HIV-1 RT as a specific target for the development of novel classes of RT inhibitors.
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Yu X, Talukder P, Bhattacharya C, Fahmi NE, Lines JA, Dedkova LM, LaBaer J, Hecht SM, Chen S. Probing of CD4 binding pocket of HIV-1 gp120 glycoprotein using unnatural phenylalanine analogues. Bioorg Med Chem Lett 2014; 24:5699-5703. [PMID: 25453804 DOI: 10.1016/j.bmcl.2014.10.058] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/29/2014] [Revised: 10/13/2014] [Accepted: 10/17/2014] [Indexed: 01/18/2023]
Abstract
CD4-gp120 interaction is the first step for HIV-1 entry into host cells. A highly conserved pocket in gp120 protein is an attractive target for developing gp120 inhibitors or novel HIV detection tools. Here we incorporate seven phenylalanine derivatives having different sizes and steric conformations into position 43 of domain 1 of CD4 (mD1.2) to explore the architecture of the 'Phe43 cavity' of HIV-1 gp120. The results show that the conserved hydrophobic pocket in gp120 tolerates a hydrophobic side chain of residue 43 of CD protein, which is 12.2 Å in length and 8.0 Å in width. This result provides useful information for developing novel gp120 inhibitors or new HIV detection tools.
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Madathil MM, Bhattacharya C, Yu Z, Paul R, Rishel MJ, Hecht SM. Modified bleomycin disaccharides exhibiting improved tumor cell targeting. Biochemistry 2014; 53:6800-10. [PMID: 25272367 PMCID: PMC4222530 DOI: 10.1021/bi501102z] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
The bleomycins (BLMs) are a family of antitumor antibiotics used clinically for anticancer chemotherapy. Their antitumor selectivity derives at least in part from their ability to target tumor cells, a property that resides in the carbohydrate moiety of the antitumor agent. In earlier studies, we have demonstrated that the tumor cell selectivity resides in the mannose carbamoyl moiety of the BLM saccharide and that both the BLM disaccharide and monosaccharide containing the carbamoyl moiety were capable of the delivery/uptake of a conjugated cyanine dye into cultured cancer cell lines. Presently, the nature of the participation of the carbamoyl moiety has been explored further to provide compounds of utility for defining the nature of the mechanism of tumor cell recognition and uptake by BLM saccharides and in the hope that more efficient compounds could be identified. A library of seven disaccharide-Cy5** dye conjugates was prepared that are structural analogues of the BLM disaccharide. These differed from the natural BLM disaccharide in the position, orientation, and substitution of the carbamoyl group. Studies of these compounds in four matched sets of tumor and normal cell lines revealed a few that were both tumor cell selective and internalized 2-4-fold more efficiently than the natural BLM disaccharide.
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Schroeder BR, Ghare MI, Bhattacharya C, Paul R, Yu Z, Zaleski PA, Bozeman TC, Rishel MJ, Hecht SM. The disaccharide moiety of bleomycin facilitates uptake by cancer cells. J Am Chem Soc 2014; 136:13641-56. [PMID: 25184545 PMCID: PMC4183664 DOI: 10.1021/ja507255g] [Citation(s) in RCA: 91] [Impact Index Per Article: 9.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
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The disaccharide moiety is responsible
for the tumor cell targeting
properties of bleomycin (BLM). While the aglycon (deglycobleomycin)
mediates DNA cleavage in much the same fashion as bleomycin, it exhibits
diminished cytotoxicity in comparison to BLM. These findings suggested
that BLM might be modular in nature, composed of tumor-seeking and
tumoricidal domains. To explore this possibility, BLM analogues were
prepared in which the disaccharide moiety was attached to deglycobleomycin
at novel positions, namely, via the threonine moiety or C-terminal
substituent. The analogues were compared with BLM and deglycoBLM for
DNA cleavage, cancer cell uptake, and cytotoxic activity. BLM is more
potent than deglycoBLM in supercoiled plasmid DNA relaxation, while
the analogue having the disaccharide on threonine was less active
than deglycoBLM and the analogue containing the C-terminal disaccharide
was slightly more potent. While having unexceptional DNA cleavage
potencies, both glycosylated analogues were more cytotoxic to cultured
DU145 prostate cancer cells than deglycoBLM. Dye-labeled conjugates
of the cytotoxic BLM aglycons were used in imaging experiments to
determine the extent of cell uptake. The rank order of internalization
efficiencies was the same as their order of cytotoxicities toward
DU145 cells. These findings establish a role for the BLM disaccharide
in tumor targeting/uptake and suggest that the disaccharide moiety
may be capable of delivering other cytotoxins to cancer cells. While
the mechanism responsible for uptake of the BLM disaccharide selectively
by tumor cells has not yet been established, data are presented which
suggest that the metabolic shift to glycolysis in cancer cells may
provide the vehicle for selective internalization.
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Tang C, Paul A, Alam MP, Roy B, Wilson WD, Hecht SM. A short DNA sequence confers strong bleomycin binding to hairpin DNAs. J Am Chem Soc 2014; 136:13715-26. [PMID: 25188011 PMCID: PMC4183661 DOI: 10.1021/ja505733u] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
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Bleomycins A5 and B2 were used to study the
structural features in hairpin DNAs conducive to strong BLM–DNA
interaction. Two members of a 10-hairpin DNA library previously found
to bind most tightly to these BLMs were subsequently noted to share
the sequence 5′-ACGC (complementary strand sequence 5′-GCGT).
Each underwent double-strand cleavage at five sites within, or near,
an eight base pair region of the DNA duplex which had been randomized
to create the original library. A new hairpin DNA library was selected
based on affinity for immobilized Fe(III)·BLM A5.
Two of the 30 newly identified DNAs also contained the sequence 5′-ACGC/5′-GCGT.
These DNAs bound to the Fe(II)·BLMs more tightly than any DNA
characterized previously. Surface plasmon resonance confirmed tight
Fe(III)·BLM B2 binding and gave an excellent fit for
a 1:1 binding model, implying the absence of significant secondary
binding sites. Fe(II)·BLM A5 was used to assess sites
of double-strand DNA cleavage. Both hairpin DNAs underwent double-strand
cleavage at five sites within or near the original randomized eight
base region. For DNA 12, four of the five double-strand
cleavages involved independent single-strand cleavage reactions; DNA 13 underwent double-strand DNA cleavage by independent single-strand
cleavages at all five sites. DNA 14, which bound Fe·BLM
poorly, was converted to a strong binder (DNA 15) by
insertion of the sequence 5′-ACGC/5′-GCGT. These findings
reinforce the idea that tighter DNA binding by Fe·BLM leads to
increased double-strand cleavage by a novel mechanism and identify
a specific DNA motif conducive to strong BLM binding and cleavage.
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