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Shen X, Zhang Y, Xu J, Yu X, Bai W, Huang X, Lei H. Central Chirality and Axial Chirality Recognition of the Enantioselective Antibodies to Herbicide Metolachlor. JOURNAL OF AGRICULTURAL AND FOOD CHEMISTRY 2024; 72:10055-10064. [PMID: 38634336 DOI: 10.1021/acs.jafc.4c00860] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 04/19/2024]
Abstract
Enantioselective antibodies have emerged as efficient tools in the field of chiral chemical detection and separation. However, it is complicated to obtain a highly stereoselective antibody due to the unclear recognition mechanism. In this study, the hapten of metolachlor was synthesized and enantio-separated. The absolute configuration of the four haptens obtained was identified by the computed and experimental electronic circular dichroism comparison. Five polyclonal antibodies against the Rac-metolachlor and its enantiomers were generated by immunization. The cross-activity of all the 5 antibodies with 44 structural analogues, including metolachlor enantiomers, was tested. It demonstrated that antibodies have higher specificity to recognize central chirality than axial chirality. Especially, αRR-MET-Ab exhibited excellent specificity and stereoselectivity. Accordingly, 3D-QSAR models were constructed and revealed that paired stereoisomers exhibited opposite interactions with the antibodies. It is the first time that the antibodies against four stereoisomers were prepared and analyzed, which will be conducive to the rational design of the stereoselective antibodies.
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Affiliation(s)
- Xing Shen
- Guangdong Provincial Key Laboratory of Food Quality and Safety, College of Food Science, South China Agricultural University, Guangzhou 510642, China
| | - Yan Zhang
- Guangdong Provincial Key Laboratory of Food Quality and Safety, College of Food Science, South China Agricultural University, Guangzhou 510642, China
| | - JingJing Xu
- Guangdong Provincial Key Laboratory of Food Quality and Safety, College of Food Science, South China Agricultural University, Guangzhou 510642, China
| | - XiaoTing Yu
- Guangdong Provincial Key Laboratory of Food Quality and Safety, College of Food Science, South China Agricultural University, Guangzhou 510642, China
| | - WenMing Bai
- Guangdong Provincial Key Laboratory of Food Quality and Safety, College of Food Science, South China Agricultural University, Guangzhou 510642, China
| | - Xinan Huang
- Institute of Tropical Medicine, Guangzhou University of Chinese Medicine, Guangzhou 510400, China
| | - HongTao Lei
- Guangdong Provincial Key Laboratory of Food Quality and Safety, College of Food Science, South China Agricultural University, Guangzhou 510642, China
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2
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Oukacine F, Ravelet C, Peyrin E. Enantiomeric sensing and separation by nucleic acids. Trends Analyt Chem 2020. [DOI: 10.1016/j.trac.2019.115733] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
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4
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Zheng X, Li Z, Beeram S, Podariu M, Matsuda R, Pfaunmiller EL, White CJ, Carter N, Hage DS. Analysis of biomolecular interactions using affinity microcolumns: a review. J Chromatogr B Analyt Technol Biomed Life Sci 2014; 968:49-63. [PMID: 24572459 PMCID: PMC4112177 DOI: 10.1016/j.jchromb.2014.01.026] [Citation(s) in RCA: 52] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/30/2013] [Revised: 01/16/2014] [Accepted: 01/19/2014] [Indexed: 12/15/2022]
Abstract
Affinity chromatography has become an important tool for characterizing biomolecular interactions. The use of affinity microcolumns, which contain immobilized binding agents and have volumes in the mid-to-low microliter range, has received particular attention in recent years. Potential advantages of affinity microcolumns include the many analysis and detection formats that can be used with these columns, as well as the need for only small amounts of supports and immobilized binding agents. This review examines how affinity microcolumns have been used to examine biomolecular interactions. Both capillary-based microcolumns and short microcolumns are considered. The use of affinity microcolumns with zonal elution and frontal analysis methods are discussed. The techniques of peak decay analysis, ultrafast affinity extraction, split-peak analysis, and band-broadening studies are also explored. The principles of these methods are examined and various applications are provided to illustrate the use of these methods with affinity microcolumns. It is shown how these techniques can be utilized to provide information on the binding strength and kinetics of an interaction, as well as on the number and types of binding sites. It is further demonstrated how information on competition or displacement effects can be obtained by these methods.
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Affiliation(s)
- Xiwei Zheng
- Department of Chemistry, University of Nebraska-Lincoln, Lincoln, NE 68588-0304, USA
| | - Zhao Li
- Department of Chemistry, University of Nebraska-Lincoln, Lincoln, NE 68588-0304, USA
| | - Sandya Beeram
- Department of Chemistry, University of Nebraska-Lincoln, Lincoln, NE 68588-0304, USA
| | - Maria Podariu
- Department of Chemistry, University of Nebraska-Lincoln, Lincoln, NE 68588-0304, USA
| | - Ryan Matsuda
- Department of Chemistry, University of Nebraska-Lincoln, Lincoln, NE 68588-0304, USA
| | - Erika L Pfaunmiller
- Department of Chemistry, University of Nebraska-Lincoln, Lincoln, NE 68588-0304, USA
| | - Christopher J White
- Department of Chemistry, University of Nebraska-Lincoln, Lincoln, NE 68588-0304, USA
| | - NaTasha Carter
- Department of Chemistry, University of Nebraska-Lincoln, Lincoln, NE 68588-0304, USA
| | - David S Hage
- Department of Chemistry, University of Nebraska-Lincoln, Lincoln, NE 68588-0304, USA.
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5
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Eleniste PP, Hofstetter H, Hofstetter O. Expression and characterization of an enantioselective antigen-binding fragment directed against α-amino acids. Protein Expr Purif 2013; 91:20-9. [PMID: 23827208 PMCID: PMC3816624 DOI: 10.1016/j.pep.2013.06.010] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/30/2013] [Revised: 06/19/2013] [Accepted: 06/24/2013] [Indexed: 11/18/2022]
Abstract
This work describes the design and expression of a stereoselective Fab that possesses binding properties comparable to those displayed by the parent monoclonal antibody. Utilizing mRNA from hybridoma clones that secrete a stereoselective anti-l-amino acid antibody, a corresponding biotechnologically produced Fab was generated. For that, appropriate primers were designed based on extensive literature and databank searches. Using these primers in PCR resulted in successful amplification of the VH, VL, CL and CH1 gene fragments. Overlap PCR was utilized to combine the VH and CH1 sequences and the VL and CL sequences, respectively, to obtain the genes encoding the HC and LC fragments. These sequences were separately cloned into the pEXP5-CT/TOPO expression vector and used for transfection of BL21(DE3) cells. Separate expression of the two chains, followed by assembly in a refolding buffer, yielded an Fab that was demonstrated to bind to l-amino acids but not to recognize the corresponding d-enantiomers.
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Affiliation(s)
| | - Heike Hofstetter
- Department of Chemistry and Biochemistry, Northern Illinois University,
DeKalb, Illinois 60115, USA
| | - Oliver Hofstetter
- Department of Chemistry and Biochemistry, Northern Illinois University,
DeKalb, Illinois 60115, USA
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Yashima E, Iida H, Okamoto Y. Enantiomeric Differentiation by Synthetic Helical Polymers. Top Curr Chem (Cham) 2013; 340:41-72. [DOI: 10.1007/128_2013_439] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022]
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7
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Fanning SW, Horn JR. An anti-hapten camelid antibody reveals a cryptic binding site with significant energetic contributions from a nonhypervariable loop. Protein Sci 2011; 20:1196-207. [PMID: 21557375 DOI: 10.1002/pro.648] [Citation(s) in RCA: 49] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/04/2011] [Revised: 04/26/2011] [Accepted: 04/26/2011] [Indexed: 11/11/2022]
Abstract
Conventional anti-hapten antibodies typically bind low-molecular weight compounds (haptens) in the crevice between the variable heavy and light chains. Conversely, heavy chain-only camelid antibodies, which lack a light chain, must rely entirely on a single variable domain to recognize haptens. While several anti-hapten VHHs have been generated, little is known regarding the underlying structural and thermodynamic basis for hapten recognition. Here, an anti-methotrexate VHH (anti-MTX VHH) was generated using grafting methods whereby the three complementarity determining regions (CDRs) were inserted onto an existing VHH framework. Thermodynamic analysis of the anti-MTX VHH CDR1-3 Graft revealed a micromolar binding affinity, while the crystal structure of the complex revealed a somewhat surprising noncanonical binding site which involved MTX tunneling under the CDR1 loop. Due to the close proximity of MTX to CDR4, a nonhypervariable loop, the CDR4 loop sequence was subsequently introduced into the CDR1-3 graft, which resulted in a dramatic 1000-fold increase in the binding affinity. Crystal structure analysis of both the free and complex anti-MTX CDR1-4 graft revealed CDR4 plays a significant role in both intermolecular contacts and binding site conformation that appear to contribute toward high affinity binding. Additionally, the anti-MTX VHH possessed relatively high specificity for MTX over closely related compounds aminopterin and folate, demonstrating that VHH domains are capable of binding low-molecular weight ligands with high affinity and specificity, despite their reduced interface.
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Affiliation(s)
- Sean W Fanning
- Department of Chemistry and Biochemistry, Northern Illinois University, DeKalb, IL 60115, USA
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Kassa T, Undesser LP, Hofstetter H, Hofstetter O. Antibody-based multiplex analysis of structurally closely related chiral molecules. Analyst 2011; 136:1113-5. [PMID: 21240425 DOI: 10.1039/c0an00814a] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Four class-specific and stereoselective antibodies were labeled with different fluorophores to enable simultaneous quantification of the enantiomers of phenylalanine and phenyllactic acid. Using fluorescence immunoassays and microarrays, sensitive detection of each analyte was possible even in the presence of a large excess of the other structurally similar molecules.
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Affiliation(s)
- Tigabu Kassa
- Department of Chemistry and Biochemistry, Northern Illinois University, DeKalb, IL 60115, USA
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9
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Kim YS, Hyun CJ, Kim IA, Gu MB. Isolation and characterization of enantioselective DNA aptamers for ibuprofen. Bioorg Med Chem 2010; 18:3467-73. [PMID: 20456958 DOI: 10.1016/j.bmc.2010.03.074] [Citation(s) in RCA: 37] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/05/2010] [Revised: 03/26/2010] [Accepted: 03/27/2010] [Indexed: 01/22/2023]
Abstract
Single stranded DNA aptamers that can bind to ibuprofen, a widely used anti-inflammation drug, were selected from random DNA library of 10(15) nucleotides by FluMag-SELEX process. Five different sequences were selected and their enantioselectivity and affinity were characterized. Three out of five aptamer candidates did not show any affinity to (S)-ibuprofen, but only to racemic form of ibuprofen, suggesting that they are (R)-ibuprofen specific aptamers. Another two aptamer candidates showed affinity to both racemic form and (S)-ibuprofen, which were considered as (S)-ibuprofen specific aptamers. The affinity of five ssDNA aptamers isolated was in a range of 1.5-5.2microM. In addition, all of these five aptamers did not show any affinity to analogues of ibuprofen in its profen's group (fenoprofen, flubiprofen, and naproxen) and the antibiotics of oxytetracycline, another control.
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Affiliation(s)
- Yeon Seok Kim
- School of Life Sciences and Biotechnology, Korea University, Anam-dong, Seongbuk-Gu, Seoul 136-701, South Korea
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10
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Franco EJ, Sonneson GJ, DeLegge TJ, Hofstetter H, Horn JR, Hofstetter O. Production and characterization of a genetically engineered anti-caffeine camelid antibody and its use in immunoaffinity chromatography. J Chromatogr B Analyt Technol Biomed Life Sci 2010; 878:177-86. [DOI: 10.1016/j.jchromb.2009.06.017] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/31/2009] [Revised: 06/08/2009] [Accepted: 06/09/2009] [Indexed: 11/16/2022]
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11
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Chiral ligand-exchange chromatography of amino acids using porous graphitic carbon coated with a dinaphthyl derivative of neamine. Anal Bioanal Chem 2008; 393:655-60. [DOI: 10.1007/s00216-008-2488-8] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/09/2008] [Revised: 10/10/2008] [Accepted: 10/15/2008] [Indexed: 11/25/2022]
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12
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HAGINAKA J. Recent progresses in protein-based chiral stationary phases for enantioseparations in liquid chromatography☆. J Chromatogr B Analyt Technol Biomed Life Sci 2008; 875:12-9. [DOI: 10.1016/j.jchromb.2008.05.022] [Citation(s) in RCA: 60] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/22/2008] [Revised: 05/02/2008] [Accepted: 05/11/2008] [Indexed: 10/22/2022]
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13
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Diamanti S, Arifuzzaman S, Elsen A, Genzer J, Vaia RA. Reactive patterning via post-functionalization of polymer brushes utilizing disuccinimidyl carbonate activation to couple primary amines. POLYMER 2008. [DOI: 10.1016/j.polymer.2008.06.020] [Citation(s) in RCA: 50] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
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14
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Copper(II) complexes of lipophilic aminoglycoside derivatives for the amino acid enantiomeric separation by ligand-exchange liquid chromatography. J Chromatogr A 2008; 1185:291-5. [DOI: 10.1016/j.chroma.2008.02.017] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/21/2007] [Revised: 02/05/2008] [Accepted: 02/06/2008] [Indexed: 11/18/2022]
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15
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Ranieri DI, Corgliano DM, Franco EJ, Hofstetter H, Hofstetter O. Investigation of the stereoselectivity of an anti-amino acid antibody using molecular modeling and ligand docking. Chirality 2008; 20:559-70. [DOI: 10.1002/chir.20522] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
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16
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Franco EJ, Hofstetter H, Hofstetter O. A comparative evaluation of random and site-specific immobilization techniques for the preparation of antibody-based chiral stationary phases. J Sep Sci 2007; 29:1458-69. [PMID: 16894791 DOI: 10.1002/jssc.200600062] [Citation(s) in RCA: 42] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Abstract
In this study, one random and four site-directed conjugation strategies were applied to immobilize an mAb, which stereoselectively binds to L-amino acids, onto silica particles. The resulting chiral stationary phases (CSPs) were used for enantiomer separation of the model-analyte D,L-phenylalanine and further examined in frontal affinity chromatography. Although random immobilization of the antibody onto discuccinimidyl carbonate-activated silica resulted in a CSP that enabled baseline separation of the enantiomers of D,L-phenylalanine, the amount of available binding sites was considerably lower compared to the CSPs prepared by site-directed strategies. Immobilization of antibody via its carbohydrate chains, either directly via hydrazone bonds between the support and the protein or indirectly via binding carbohydrate-biotinylated antibody to streptavidin-derivatized silica, resulted in medium column efficiencies. Higher amounts of available active sites were obtained by immobilizing the antibody indirectly through the "crystallizable fragment (Fc)" receptor protein A/G. The best results with regard to amount of available binding sites and column efficiency were obtained by first biotinylating the antibody specifically at its C-termini using carboxypeptidase Y and immobilizing the biotinylated antibody on streptavidin-derivatized silica.
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Affiliation(s)
- Elliott J Franco
- Department of Chemistry and Biochemistry, Northern Illinois University, DeKalb, IL 60115-2862, USA
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Franco EJ, Hofstetter H, Hofstetter O. Enantiomer separation of alpha-hydroxy acids in high-performance immunoaffinity chromatography. J Pharm Biomed Anal 2007; 46:907-13. [PMID: 18022339 DOI: 10.1016/j.jpba.2007.10.004] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/28/2007] [Accepted: 10/05/2007] [Indexed: 10/22/2022]
Abstract
In this study, a monoclonal anti-d-hydroxy acid antibody was immobilized onto a synthetic high-flow-through chromatographic support material to produce a chiral stationary phase suitable for enantiomer separation of free alpha-hydroxy acids. Chiral separation of several aliphatic and aromatic members of this class of compounds was achieved in HPLC under mild isocratic buffer conditions using phosphate buffered saline, pH 7.4, as mobile phase. Due to the high degree of stereoselectivity exhibited by the immobilized antibody, in all cases the l-enantiomer eluted with the void volume, while the d-enantiomer was retained and eluted second. The effect of the mobile phase parameters flow rate, temperature, pH, and ionic strength on the enantiomer separation of the model analyte mandelic acid was investigated. While it was found that variations in the flow rate did not change the retention factor k2, dramatic effects on the interaction between the immobilized antibody and d-mandelic acid were observed when any of the other mobile phase parameters were modulated.
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Affiliation(s)
- Elliott J Franco
- Department of Chemistry and Biochemistry, Northern Illinois University, DeKalb, IL 60115-2862, USA
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Zeleke JM, Smith GB, Hofstetter H, Hofstetter O. Enantiomer separation of amino acids in immunoaffinity micro LC-MS. Chirality 2007; 18:544-50. [PMID: 16642491 DOI: 10.1002/chir.20286] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
Chiral immunoaffinity microbore columns were directly interfaced with MS detection, and the effect of column length and temperature on the enantiomer separation of a number of underivatized aromatic and aliphatic amino acids was investigated utilizing an antibody chiral stationary phase that had been prepared by immobilizing a monoclonal anti-D-amino acid antibody onto silica. The stronger affinity of the antibody towards aromatic and bulky amino acids allowed separation of such analytes in a 0.75 x 150 mm column, while an increase in column length enabled separation of more weakly bound compounds. The strength of interaction between chiral selector and analytes could be modulated conveniently by lowering the temperature. For the first time, simultaneous enantiomer separation of mixtures of amino acids was achieved on antibody-based chiral stationary phases using extracted ion chromatograms.
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Affiliation(s)
- Jessica M Zeleke
- Department of Chemistry and Biochemistry, Northern Illinois University, DeKalb, Illinois 60115-2862, USA
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Kovarik P, Hodgson RJ, Covey T, Brook MA, Brennan JD. Capillary-scale frontal affinity chromatography/MALDI tandem mass spectrometry using protein-doped monolithic silica columns. Anal Chem 2007; 77:3340-50. [PMID: 15889927 DOI: 10.1021/ac048263p] [Citation(s) in RCA: 45] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Frontal affinity chromatography (FAC) interfaced with electrospray mass spectrometry (ESI-MS) has been reported as a potential method for screening of compound mixtures against immobilized target proteins. However, the interfacing of bioaffinity columns to ESI-MS requires that the eluent that passes through the protein-loaded column have a relatively low ionic strength to produce a stable spray. Such low ionic strength solvents can cause serious problems with protein stability and may also affect binding constants and lead to high nonspecific binding to the column. Herein, we report on the interfacing of bioaffinity columns to matrix-assisted laser desorption/ionization (MALDI) MS/MS as a new platform for FAC/MS studies. Capillary columns containing a monolithic silica material with entrapped dihydrofolate reductase were used for frontal affinity chromatography of small-molecule mixtures. The output from the column was combined with a second stream containing alpha-cyano-hydoxycinnamic acid in methanol and was deposited using a nebulizer-assisted electrospray method onto a conventional MALDI plate that moved relative to the column via a computer-controlled x-y stage, creating a semipermanent record of the FAC run. The use of MALDI MS/MS allowed for buffers with significantly higher ionic strength to be used for FAC studies, which reduced nonspecific binding of ionic compounds and allowed for better retention of protein activity over multiple runs. Following deposition, MALDI analysis required only a fraction of the chromatographic run time, and the deposited track could be rerun multiple times to optimize ionization parameters and allow signal averaging to improve the signal-to-noise ratio. Furthermore, high levels of potential inhibitors could be detected via MALDI with limited ion suppression effects. Both MALDI- and ESI-based analysis showed similar retention of inhibitors present in compound mixtures when using identical ionic strength conditions. The results show that FAC/MALDI-MS should provide advantages over FAC/ESI-MS for high-throughput screening of compound mixtures.
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Affiliation(s)
- Peter Kovarik
- MDS/Sciex, 71 Four Valley Drive, Concord, Ontario L4K 4V8, Canada
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Koidl J, Hödl H, Schmid MG, Konrad M, Petschauer S, Kostner GM, Gübitz G. Chiral separation of T3 enantiomers using stereoselective antibodies as a selector in micro-HPLC. JOURNAL OF BIOCHEMICAL AND BIOPHYSICAL METHODS 2006; 69:33-42. [PMID: 16697467 DOI: 10.1016/j.jbbm.2006.03.015] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/28/2005] [Revised: 03/21/2006] [Accepted: 03/26/2006] [Indexed: 11/19/2022]
Abstract
This work deals with the application of stereoselective antibodies against L-T3 as a tailor-made chiral selector in micro-HPLC. The separations were performed in microbore columns using commercially available anti-L-T3 antibodies chemically bonded to 5 microm silica gel. The enantiomers of T3 were baseline separated under mild continuous isocratic elution conditions using 10 mM phosphate buffer, pH 7.4. The D-enantiomer eluted with the void volume, while the L-enantiomer was retained by the antibody phase and eluted second. An indirect competitive and non-competitive enzyme linked immunosorbent assay (ELISA) was used for testing the stereoselectivity of anti-L-T3 antibodies.
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Affiliation(s)
- Julia Koidl
- Institute of Pharmaceutical Sciences, Department of Pharmaceutical Chemistry, Karl-Franzens-University, Universitätsplatz 1, A-8010 Graz, Austria
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Gübitz G, Schmid MG. Chiral separation principles in chromatographic and electromigration techniques. Mol Biotechnol 2006; 32:159-80. [PMID: 16444017 DOI: 10.1385/mb:32:2:159] [Citation(s) in RCA: 83] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
Almost half of the drugs in use today are chiral. It is well established that the pharmacological activity is mostly restricted to one of the enantiomers (eutomer). There can be qualitative and quantitative differences in the activity of the enantiomers. In many cases, the inactive enantiomer (distomer) shows unwanted side effects or even toxic effects. Even if the side effects are not that drastic, the distomer has to be metabolized and this represents an unnecessary burden for the organism. Therefore, the development of methods for the separation of enantiomers, both on analytical and preparative scale, has become increasingly important. Chromatographic techniques such as thin layer chromatography (TLC), gas chromatography (GC), supercritical fluid chromatography (SFC), and above all high-performance liquid chromatography (HPLC) have been used for enantiomer separation for about two decades. More recently, electromigration techniques, such as capillary electrophoresis and capillary electrochromatography, have been shown to be powerful alternatives to chromatographic methods. This review gives a short overview of different chiral separation principles and their application. Several new developments are discussed.
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Affiliation(s)
- Gerald Gübitz
- Institute of Pharmaceutical Sciences, Department of Pharmaceutical Chemistry, Karl-Franzens University, Universitätsplatz 1, A-8010 Graz, Austria
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22
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Parkkinen T, Nevanen TK, Koivula A, Rouvinen J. Crystal Structures of an Enantioselective Fab-fragment in Free and Complex Forms. J Mol Biol 2006; 357:471-80. [PMID: 16427081 DOI: 10.1016/j.jmb.2005.12.045] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/23/2005] [Revised: 12/09/2005] [Accepted: 12/12/2005] [Indexed: 10/25/2022]
Abstract
Enantioselective antibodies can separate the enantiomers of a chiral compound in a highly specific manner. We have recently reported the cloning and applications of a recombinant Fab-fragment, ENA11His, in the enantioseparation of a drug candidate, finrozole, which contains two chiral centers. Here, the crystal structures of this enantioselective antibody Fab-fragment are determined in the absence of the hapten at a resolution of 2.75 A, and in the presence of the hapten at 2.05 A resolution. The conformation of the protein was found to be similar in both free and complex forms. The hapten molecule was tightly bound in a deep cleft between the light and heavy chains of the Fab-fragment. The complex structure also allowed us to describe the molecular basis for enantioselectivity and to deduce the absolute configurations of all the four different stereoisomers (a-d) of finrozole. The ENA11His antibody fragment selectively binds the SR (a) enantiomer from the racemic mixture of a and d-enantiomers, thus allowing separation from the pharmacologically most active RS enantiomer (d). In particular, Asp95 and Asn35 of the H-chain in the ENA11 His antibody seem to provide this specificity through hydrogen bonding.
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Affiliation(s)
- Tarja Parkkinen
- Department of Chemistry, University of Joensuu, PO Box 111, FIN-80101 Joensuu, Finland
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Besanger TR, Hodgson RJ, Green JRA, Brennan JD. Immobilized enzyme reactor chromatography: Optimization of protein retention and enzyme activity in monolithic silica stationary phases. Anal Chim Acta 2006; 564:106-15. [PMID: 17723368 DOI: 10.1016/j.aca.2005.12.066] [Citation(s) in RCA: 35] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/20/2005] [Revised: 12/19/2005] [Accepted: 12/29/2005] [Indexed: 11/22/2022]
Abstract
Our group recently reported on the application of protein-doped monolithic silica columns for immobilized enzyme reactor chromatography, which allowed screening of enzyme inhibitors present in mixtures using mass spectrometry for detection. The enzyme was immobilized by entrapment within a bimodal meso/macroporous silica material prepared by a biocompatible sol-gel processing route. While such columns proved to be useful for applications such as screening of protein-ligand interactions, significant amounts of entrapped proteins leached from the columns owing to the high proportion of macropores within the materials. Herein, we describe a detailed study of factors affecting the morphology of protein-doped bioaffinity columns and demonstrate that specific pH values and concentrations of poly(ethylene glycol) can be used to prepare essentially mesoporous columns that retain over 80% of initially loaded enzyme in an active and accessible form and yet still retain sufficient porosity to allow pressure-driven flow in the low muL/min range. Using the enzyme gamma-glutamyl transpeptidase (gamma-GT), we further evaluated the catalytic constants of the enzyme entrapped in capillary columns with different silica morphologies as a function of flowrate and backpressure using the enzyme reactor assay mode. It was found that the apparent activity of the enzyme was highest in mesoporous columns that retained high levels of enzyme. In such columns, enzyme activity increased by approximately 2-fold with increases in both flowrate (from 250 to 1000 nL/min) and backpressure generated (from 500 to 2100 psi) during the chromatographic activity assay owing to increases in k(cat) and decreases in K(M), switching from diffusion controlled to reaction controlled conditions at ca. 2000 psi. These results suggest that columns with minimal macropore volumes (<5%) are advantageous for the entrapment of soluble proteins for bioaffinity and bioreactor chromatography.
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Affiliation(s)
- Travis R Besanger
- Department of Chemistry, McMaster University, 1280 Main St. West, Hamilton, Ont. L8S 4M1, Canada
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Besanger TR, Hodgson RJ, Guillon D, Brennan JD. Monolithic membrane-receptor columns: Optimization of column performance for frontal affinity chromatography/mass spectrometry applications. Anal Chim Acta 2006. [DOI: 10.1016/j.aca.2005.12.062] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
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25
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Hofstetter H, Hofstetter O. Antibodies as tailor-made chiral selectors for detection and separation of stereoisomers. Trends Analyt Chem 2005. [DOI: 10.1016/j.trac.2005.04.018] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/25/2022]
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26
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Ravelet C, Boulkedid R, Ravel A, Grosset C, Villet A, Fize J, Peyrin E. A L-RNA aptamer chiral stationary phase for the resolution of target and related compounds. J Chromatogr A 2005; 1076:62-70. [PMID: 15974070 DOI: 10.1016/j.chroma.2005.03.132] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
In this paper, we report for the first time an aptamer-based chiral stationary phase (CSP) able to resolve racemates of both target and various related compounds. The enantiomers of tyrosine and analogues (11 enantiomeric pairs) were separated using an immobilized tyrosine-specific L-RNA aptamer as CSP and an aqueous buffer (8 mM Tris-HCl buffer, 25 mM NaCl, 5 mM MgCl2; pH 7.4) as mobile phase, at a column temperature of 10 degrees C. It appeared that the carboxylic and amino groups as well as the aromatic side chain of amino acid controlled the stereospecific recognition. Modifications on the polar groups were strongly detrimental for enantioselectivity while the replacement of the phenolic group by some bicyclic aromatic residues of different polarity, size or shape did not impair the enantioselective interaction. In addition, the effects of the mobile phase composition and column temperature upon the retention and stereoselective properties of the CSP were assessed. Finally, it was found that the immobilized RNA aptamer could be used under hydro-organic mobile phase conditions without alteration of the stationary phase stability.
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Affiliation(s)
- Corinne Ravelet
- Département de Pharmacochimie Moléculaire UMR 5063 CNRS, Institut de Chimie Moléculaire de Grenoble FR 2607, Université Joseph Fourier, UFR de Pharmacie de Grenoble, Avenue de Verdun, 38240 Meylan, France
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27
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He L, Toh CS. Recent advances in analytical chemistry--a material approach. Anal Chim Acta 2005; 556:1-15. [PMID: 17723326 DOI: 10.1016/j.aca.2005.08.042] [Citation(s) in RCA: 85] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/31/2005] [Revised: 08/12/2005] [Accepted: 08/16/2005] [Indexed: 11/24/2022]
Abstract
Advancements of materials research have profound direct impacts on developments in analytical chemistry and may hold the key to improvement of existing or new techniques at present times and near future. Applications of materials in analytical chemistry are reviewed, with focus on sensors, separations and extraction techniques. This review aims to survey examples of interesting works carried out in the last five years over a broad spectrum of materials classified as hybrids, nanomaterials and biomolecular materials.
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Affiliation(s)
- Lin He
- Department of Chemistry, Faculty of Science, National University of Singapore, 3 Science Drive 3, Singapore 117543, Singapore
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28
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Hofstetter H, Cary JR, Eleniste PP, Hertweck JK, Lindstrom HJ, Ranieri DI, Smith GB, Undesser LP, Zeleke JM, Zeleke TK, Hofstetter O. New developments in the production and use of stereoselective antibodies. Chirality 2005; 17 Suppl:S9-18. [PMID: 15612044 DOI: 10.1002/chir.20099] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
This article describes the production of stereoselective antibodies using both classical immunological and modern molecular biological techniques. Stereoselective antibodies against alpha-hydroxy acids were raised in rabbits and mice and compared with previously produced anti-alpha-amino acid antibodies. It was found that both types of antibodies combine stereoselectivity with class-specificity. Sequence analyses revealed that antibodies with opposing stereoselectivities can be formed during the affinity maturation process from a common progenitor or independently using nonhomologous binding sites. For the first time, phage display was employed to obtain stereoselective antibody fragments. The versatility of stereoselective antibodies as chiral selectors was demonstrated by applying them in several immunosensors and in chiral chromatography. A simple, membrane-based optical sensor allowed detection of enantiomeric impurities at the 1/2,000 level (99.9% ee). Silica-based antibody chiral stationary phases could be used for enantiomer separation of aliphatic amino acids in standard-sized columns, while miniaturized columns allowed interfacing with an MS-detector.
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Affiliation(s)
- Heike Hofstetter
- Department of Chemistry and Biochemistry, Northern Illinois University, DeKalb, Illinois 60115-2862, USA
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29
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Trojanowicz M, Wcisło M. Electrochemical and Piezoelectric Enantioselective Sensors and Biosensors. ANAL LETT 2005. [DOI: 10.1081/al-200050157] [Citation(s) in RCA: 46] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/03/2022]
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Schweitzer MH, Wittmeyer J, Avci R, Pincus S. Experimental support for an immunological approach to the search for life on other planets. ASTROBIOLOGY 2005; 5:30-47. [PMID: 15711168 DOI: 10.1089/ast.2005.5.30] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/24/2023]
Abstract
We propose a three-phase approach to test for evidence of life in extraterrestrial samples. The approach capitalizes on the flexibility, sensitivity, and specificity of antibody-antigen interactions. Data are presented to support the first phase, in which various extraction protocols are compared for efficiency, and in which a preliminary suite of antibodies are tested against various antigens. The antigens and antibodies were chosen on the basis of criteria designed to optimize the detection of extraterrestrial biomarkers unique to living or once-living organisms.
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Affiliation(s)
- Mary Higby Schweitzer
- Department of Marine, Earth and Atmospheric Sciences, North Carolina State University, Raleigh, North Carolina 27695, USA.
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31
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Chen Y, Zhang Z, Sui X, Brennan JD, Brook MA. Reduced shrinkage of sol–gel derived silicas using sugar-based silsesquioxane precursors. ACTA ACUST UNITED AC 2005. [DOI: 10.1039/b502959g] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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32
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Zeleke TK, Zeleke JM, Hofstetter H, Hofstetter O. Stereoselective antibodies to free α-hydroxy acids. J Mol Recognit 2005; 18:334-40. [PMID: 15880650 DOI: 10.1002/jmr.741] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
Abstract
This work describes antibodies exhibiting high stereoselectivity and class-specificity towards the enantiomers of free alpha-hydroxy acids. Since the antibodies interact primarily with the carboxyl-hydroxyl-hydrogen triad about the stereogenic center, they are useful for enantiomer analysis of a variety of structurally different alpha-hydroxy acids including aromatic and aliphatic compounds, e.g. lactic acid. The utility of such antibodies for enantiomer separation in chromatography was demonstrated. Comparative studies of these and previously described anti-alpha-amino acid antibodies revealed that both types of antibodies bind only to analytes that possess both the corresponding target structure and the correct configuration. Thus, substitution of an amino group for the alpha-hydroxyl group results in a complete loss of binding activity with the anti-alpha-hydroxy acid antibodies, while an alpha-amino group is essential for the interaction between analytes and anti-alpha-amino acid antibodies.
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Affiliation(s)
- Tigabu K Zeleke
- Department of Chemistry and Biochemistry, Northern Illinois University, DeKalb, IL 60115-2862, USA
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33
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Affiliation(s)
- Timothy J Ward
- Department of Chemistry, Millsaps College, 1701 North State Street, Box 150306, Jackson, Mississippi 39210, USA.
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Ravelet C, Michaud M, Ravel A, Grosset C, Villet A, Peyrin E. Streptavidin chiral stationary phase for the separation of adenosine enantiomers. J Chromatogr A 2004; 1036:155-60. [PMID: 15146916 DOI: 10.1016/j.chroma.2004.02.083] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Abstract
In this paper, a microbore column packed with streptavidin particles was used, at various temperatures (0-24 degrees C), to separate the adenosine enantiomers by HPLC. Using an aqueous mobile phase, the apparent enantioseparation was high for a small molecule, varying from 11.5 at 0 degrees C to 6.2 at 24 degrees C. From the experiments carried out with a streptavidin-biotin complex stationary phase, it was demonstrated that the blockage of the biotin sites of the immobilized streptavidin was responsible for a strong decrease in the enantioselectivity via a direct and/or an indirect effect. From the analysis of the concentration dependencies of the solute retention factor, it was also shown that a reduction of the D-adenosine specific binding sites occurred at the lowest temperature. The thermodynamic parameters determined from the van't Hoff plots indicated that the D-adenosine binding to the streptavidin specific sites was enthalpically driven.
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Affiliation(s)
- Corinne Ravelet
- Département de Pharmacochimie Moléculaire UMR 5063 CNRS-UJF, Equipe de Chimie Analytique, Université Joseph Fourier, ICMG FR 2607, UFR de Pharmacie de Grenoble, Avenue de Verdun, 38240 Meylan, France
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35
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Hodgson RJ, Chen Y, Zhang Z, Tleugabulova D, Long H, Zhao X, Organ M, Brook MA, Brennan JD. Protein-Doped Monolithic Silica Columns for Capillary Liquid Chromatography Prepared by the Sol−Gel Method: Applications to Frontal Affinity Chromatography. Anal Chem 2004; 76:2780-90. [PMID: 15144188 DOI: 10.1021/ac0352124] [Citation(s) in RCA: 74] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
The development of bioaffinity chromatography columns that are based on the entrapment of biomolecules within the pores of sol-gel-derived monolithic silica is reported. Monolithic nanoflow columns are formed by mixing the protein-compatible silica precursor diglycerylsilane with a buffered aqueous solution containing poly(ethylene oxide) (PEO, MW 10,000) and the protein of interest and then loading this mixture into a fused-silica capillary (150-250-microm i.d.). Spinodal decomposition of the PEO-doped sol into two distinct phases prior to the gelation of the silica results in a bimodal pore distribution that produces large macropores (>0.1 microm), to allow good flow of eluent with minimal back pressure, and mesopores (approximately 3-5-nm diameter) that retain a significant fraction of the entrapped protein. Addition of low levels of (3-aminopropyl)triethoxysilane is shown to minimize nonselective interactions of analytes with the column material, resulting in a column that is able to retain small molecules by virtue of their interaction with the entrapped biomolecules. Such columns are shown to be suitable for pressure-driven liquid chromatography and can be operated at relatively high flow rates (up to 500 microL x min(-1)) or with low back pressures (<100 psi) when used at flow rates of 5-10 microL x min(-1). The clinically relevant enzyme dihydrofolate reductase was entrapped within the bioaffinity columns and was used to screen mixtures of small molecules using frontal affinity chromatography with mass spectrometric detection. Inhibitors present in compound mixtures were retained via bioaffinity interactions, with the retention time being dependent on both the ligand concentration and the affinity of the ligand for the protein. The results suggest that such columns may find use in high-throughput screening of compound mixtures.
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Affiliation(s)
- Richard J Hodgson
- Department of Chemistry, McMaster University, Hamilton, Ontario, L8S 4M1, Canada
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36
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Michaud M, Jourdan E, Ravelet C, Villet A, Ravel A, Grosset C, Peyrin E. Immobilized DNA Aptamers as Target-Specific Chiral Stationary Phases for Resolution of Nucleoside and Amino Acid Derivative Enantiomers. Anal Chem 2004; 76:1015-20. [PMID: 14961733 DOI: 10.1021/ac035090f] [Citation(s) in RCA: 102] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Recently, we described the use of a DNA aptamer as a new target-specific chiral stationary phase (CSP) for the separation of oligopeptide enantiomers (Michaud, M.; Jourdan, E.; Villet, A.; Ravel, A.; Grosset, C.; Peyrin, E. J. Am. Chem. Soc. 2003, 125, 8672). However, from a practical point of view, it was fundamental to extend the applicability of such target-specific aptamer CSP to the resolution of small (bioactive) molecule enantiomers. In this paper, immobilized DNA aptamers specifically selected against D-adenosine and L-tyrosinamide were used to resolve the enantiomers by HPLC, using microbore columns. At 20 degrees C, the adenosine enantioseparation was similar to that classically reported with imprinted CSPs (approximately 3.5) while a very high enantioselectivity was observed for the tyrosinamide enantiomers (the nontarget enantiomer was essentially nonretained on the CSP). The influence of temperature on solute binding and chiral discrimination was analyzed. The binding enthalpic contributions were determined from linear van't Hoff plots. Very large DeltaH values were obtained for the target enantiomers (-71.4 +/- 0.7 kJ/mol for D-adenosine and -139.4 +/- 2.0 kJ/mol for L-tyrosinamide). Such values were consistent with the formation of a tight complex between these analytes and the aptamer CSPs. This work demonstrates that target-specific aptamer CSPs constitute a powerful tool for the resolution of small (bioactive) molecule enantiomers.
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Affiliation(s)
- Mickael Michaud
- Equipe de Chimie Analytique, Département de Pharmacochimie Moléculaire UMR 5063 CNRS-UJF, ICMG FR 2607, Université Joseph Fourier, UFR de Pharmacie de Grenoble, Avenue de Verdun, 38240 Meylan, France
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37
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Michaud M, Jourdan E, Villet A, Ravel A, Grosset C, Peyrin E. A DNA aptamer as a new target-specific chiral selector for HPLC. J Am Chem Soc 2003; 125:8672-9. [PMID: 12848575 DOI: 10.1021/ja034483t] [Citation(s) in RCA: 148] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
In this paper, a DNA aptamer, known to bind stereospecifically the D-enantiomer of an oligopeptide, i.e., arginine-vasopressin, was immobilized on a chromatographic support. The influence of various parameters (such as column temperature, eluent pH, and salt concentration) on the L- and D-peptide retention was investigated in order to provide information about the binding mechanism and then to define the utilization conditions of the aptamer column. The results suggest that dehydration at the binding interface, charge-charge interactions, and adaptive conformational transitions contribute to the specific D-peptide-aptamer complex formation. A very significant enantioselectivity was obtained in the optimal binding conditions, the D-peptide being strongly retained by the column while the L-peptide eluted in the void volume. A rapid baseline separation of peptide enantiomers was also achieved by modulating the elution conditions. Furthermore, it was established that the aptamer column was stable during an extended period of time. This work indicates that DNA aptamers, specifically selected against an enantiomer, could soon become very attractive as new target-specific chiral selectors for HPLC.
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Affiliation(s)
- Mickael Michaud
- Equipe de Chimie Analytique, Département de Pharmacochimie Moléculaire (UMR 5063 CNRS-UJF), ICMG FR 2607, UFR de Pharmacie de Grenoble, Université Joseph Fourier, Avenue de Verdun, 38240 Meylan, France
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Dutta P, Tipple CA, Lavrik NV, Datskos PG, Hofstetter H, Hofstetter O, Sepaniak MJ. Enantioselective sensors based on antibody-mediated nanomechanics. Anal Chem 2003; 75:2342-8. [PMID: 12918975 DOI: 10.1021/ac034031z] [Citation(s) in RCA: 73] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
The use of microfabricated cantilevers as bioaffinity sensors was investigated. Since many bioaffinity interactions involve proteins as receptors, we conducted studies of the magnitude, kinetics, and reversibility of surface stresses caused when common proteins interact with microcantilevers (MCs) with nanostructured (roughened) gold surfaces on one side. Exposure of nanostructured, unfunctionalized MCs to the proteins immunoglobulin G and bovine serum albumin (BSA) resulted in reversible large tensile stresses, whereas MCs with smooth gold surfaces on one side produced reversible responses that were considerably smaller and compressive. The response magnitude for nanostructured MCs exposed to BSA is shown to be concentration dependent, and linear calibration over the range of 1-200 mg/L is demonstrated. Stable, reusable protein bioaffinity phases based on unique enantioselective antibodies are created by covalently linking monoclonal antibodies to nanostructured MC surfaces. The direct (label-free) stereoselective detection of trace amounts of an important class of chiral analytes, the alpha-amino acids, was achieved based on immunomechanical responses involving nanoscale bending of the cantilever. The temporal response of the cantilever (delta deflection/delta time) is linearly proportional to the analyte concentration and allows the quantitative determination of enantiomeric purity up to an enantiomeric excess of 99.8%. To our knowledge, this is the first demonstration of chiral discrimination using highly scalable microelectromechanical systems.
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Affiliation(s)
- P Dutta
- Department of Chemistry, University of Tennessee, Knoxville, Tennessee 37996-1600, USA
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