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Saleh RI, Kim S, Lee SH, Kwon H, Jeong HE, Cha C. Manipulating Physicochemical Properties of Biosensor Platform with Polysuccinimide-Silica Nanocomposite for Enhanced Protein Detection. Adv Healthc Mater 2023; 12:e2301774. [PMID: 37485740 DOI: 10.1002/adhm.202301774] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/28/2023] [Revised: 07/12/2023] [Indexed: 07/25/2023]
Abstract
As point-of-care testing (POCT) is becoming the new paradigm of medical diagnostics, there is a growing need to develop reliable POCT devices that can be conveniently operated in a minimally invasive manner. However, the clinical potential of POCT diagnostics is yet to be realized, mainly due to the limited and inconsistent amount of collected samples on these devices, undermining their accuracy. This study proposes a new biosensing platform modified with a functional polysuccinimide (PSI)-silica nanoparticle (SNP) composite system that can substantially increase the protein conjugation efficiency by modulating physicochemical interaction with proteins by several hundred percent from an unmodified device. The efficacy of this PSI-SNP system is further validated by applying it on the surface of a microneedle array (MN), which has emerged as a promising POCT device capable of accessing interstitial fluid through minimal penetration of the skin. This PSI-SNP MN is demonstrated to detect a wide array of proteins with high sensitivity on par with conventional whole serum analysis, validated by in vivo animal testing, effectively displaying broad applicability in biomedical engineering.
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Affiliation(s)
- Rabi Ibrahim Saleh
- Center for Multidimensional Programmable Matter, Department of Materials Science and Engineering, Ulsan National Institute of Science and Technology (UNIST), Ulsan, 44919, Republic of Korea
| | - Suntae Kim
- Center for Multidimensional Programmable Matter, Department of Materials Science and Engineering, Ulsan National Institute of Science and Technology (UNIST), Ulsan, 44919, Republic of Korea
| | - Sang-Hyeon Lee
- Department of Mechanical Engineering, Ulsan National Institute of Science and Technology (UNIST), Ulsan, 44919, Republic of Korea
| | - Hyukjoo Kwon
- Department of Mechanical Engineering, Ulsan National Institute of Science and Technology (UNIST), Ulsan, 44919, Republic of Korea
| | - Hoon Eui Jeong
- Department of Mechanical Engineering, Ulsan National Institute of Science and Technology (UNIST), Ulsan, 44919, Republic of Korea
| | - Chaenyung Cha
- Center for Multidimensional Programmable Matter, Department of Materials Science and Engineering, Ulsan National Institute of Science and Technology (UNIST), Ulsan, 44919, Republic of Korea
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2
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Li J, Chen J, Wang Y, Yao L. Detecting the Hydrogen Bond Cooperativity in a Protein β-Sheet by H/D Exchange. Int J Mol Sci 2022; 23:ijms232314821. [PMID: 36499147 PMCID: PMC9740688 DOI: 10.3390/ijms232314821] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/26/2022] [Revised: 11/22/2022] [Accepted: 11/24/2022] [Indexed: 12/05/2022] Open
Abstract
The hydrogen bond (H-bond) cooperativity in the β-sheet of GB3 is investigated by a NMR hydrogen/deuterium (H/D) exchange method. It is shown that the weakening of one backbone N-H…O=C H-bond between two β-strands, β1 and β2, due to the exchange of NH to ND of the H-bond donor in β1, perturbs the chemical shift of 13Cα, 13Cβ, 1Hα, 1HN, and 15N of the H-bond acceptor and its following residue in β2. Quantum mechanical calculations suggest that the -H-bond chemical shift isotope effect is caused by the structural reorganization in response to the H-bond weakening. This structural reorganization perturbs four neighboring H-bonds, with three being weaker and one being stronger, indicating that three H-bonds are cooperative and one is anticooperative with the perturbed H-bond. The sign of the cooperativity depends on the relative position of the H-bonds. This H-bond cooperativity, which contributes to β-sheet stability overall, can be important for conformational coupling across the β-sheet.
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Affiliation(s)
- Jingwen Li
- College of Chemistry and Chemical Engineering, China University of Petroleum (East China), Qingdao 266580, China
| | - Jingfei Chen
- Qingdao New Energy Shandong Laboratory, Qingdao Institute of Bioenergy and Bioprocess Technology, Chinese Academy of Sciences, Qingdao 266101, China
- Shandong Energy Institute, Qingdao 266101, China
| | - Yefei Wang
- Qingdao New Energy Shandong Laboratory, Qingdao Institute of Bioenergy and Bioprocess Technology, Chinese Academy of Sciences, Qingdao 266101, China
- Shandong Energy Institute, Qingdao 266101, China
- Correspondence: (Y.W.); (L.Y.)
| | - Lishan Yao
- Qingdao New Energy Shandong Laboratory, Qingdao Institute of Bioenergy and Bioprocess Technology, Chinese Academy of Sciences, Qingdao 266101, China
- Shandong Energy Institute, Qingdao 266101, China
- Correspondence: (Y.W.); (L.Y.)
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Oliveira JP, Queiroz MH, Provasi PF, Rivelino R. A NMR hybrid J-coupling alternation (hJCA) parameter linearly correlated to properties of intermolecular H-bonded chains. COMPUT THEOR CHEM 2022. [DOI: 10.1016/j.comptc.2022.113913] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/03/2022]
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Ali MA, Volmert B, Evans CM, Braun PV. Static and Dynamic Gradient Based Directional Transportation of Neutral Molecules in Swollen Polymer Films. Angew Chem Int Ed Engl 2022; 61:e202206061. [PMID: 36031709 PMCID: PMC9826203 DOI: 10.1002/anie.202206061] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/25/2022] [Indexed: 01/11/2023]
Abstract
Materials which selectively transport molecules offer powerful opportunities for concentrating and separating chemical agents. Here, utilizing static and dynamic chemical gradients, transport of molecules within swollen crosslinked polymers is demonstrated. Using an ≈200 μm static hydroxyl to hexyl gradient, the neutral ambipolar nerve agent surrogate diethyl (cyanomethyl)phosphonate (DECP) is directionally transported and concentrated 60-fold within 4 hours. To accelerate transport kinetics, a dynamic gradient (a "travelling wave") is utilized. Here, the non-polar dye pyrene was transported. The dynamic gradient is generated by an ion exchange process triggered by the localized introduction of an aqueous NaCl solution, which converts the gel from hydrophobic to hydrophilic. As the hydrophilic region expands, associated water enters the gel, and pyrene is pushed ahead of the expansion front. The dynamic gradient provides about 10-fold faster transport kinetics than the static gradient.
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Affiliation(s)
- Mohammad A. Ali
- Department of Materials Science and EngineeringDepartment of ChemistryBeckman Institute for Advanced Science and Technology, and Materials Research LaboratoryUniversity of Illinois Urbana ChampaignUrbanaIllinois 61801USA
| | - Brett Volmert
- Department of Materials Science and EngineeringDepartment of ChemistryBeckman Institute for Advanced Science and Technology, and Materials Research LaboratoryUniversity of Illinois Urbana ChampaignUrbanaIllinois 61801USA
| | - Christopher M. Evans
- Department of Materials Science and EngineeringDepartment of ChemistryBeckman Institute for Advanced Science and Technology, and Materials Research LaboratoryUniversity of Illinois Urbana ChampaignUrbanaIllinois 61801USA
| | - Paul V. Braun
- Department of Materials Science and EngineeringDepartment of ChemistryBeckman Institute for Advanced Science and Technology, and Materials Research LaboratoryUniversity of Illinois Urbana ChampaignUrbanaIllinois 61801USA
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5
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Ali MA, Volmert B, Evans CM, Braun PV. Static and Dynamic Gradient Based Directional Transportation of Neutral Molecules in Swollen Polymer Films. Angew Chem Int Ed Engl 2022. [DOI: 10.1002/ange.202206061] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
Affiliation(s)
- Mohammad A Ali
- University of Illinois Urbana-Champaign Materials Research Laboratory UNITED STATES
| | - Brett Volmert
- University of Illinois Urbana-Champaign Materials Science and Engineering UNITED STATES
| | - Christopher M Evans
- University of Illinois Urbana-Champaign Materials Science and Engineering UNITED STATES
| | - Paul V. Braun
- University of Illinois Urbana-Champaign Department of Materials Science and Engineering Materials Science and Engineering 1304 West Green St.Materials Science and Eng. Building 61801 Urbana UNITED STATES
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Wei G, Hu R, Li Q, Lu W, Liang H, Nan H, Lu J, Li J, Zhao Q. Oligonucleotide Discrimination Enabled by Tannic Acid-Coordinated Film-Coated Solid-State Nanopores. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2022; 38:6443-6453. [PMID: 35544765 DOI: 10.1021/acs.langmuir.2c00638] [Citation(s) in RCA: 8] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/12/2023]
Abstract
Discrimination of nucleotides serves as the basis for DNA sequencing using solid-state nanopores. However, the translocation of DNA is usually too fast to be detected, not to mention nucleotide discrimination. Here, we utilized polyphenolic TA and Fe3+, an attractive metal-organic thin film, and achieved a fast and robust surface coating for silicon nitride nanopores. The hydrophilic coating layer can greatly reduce the low-frequency noise of an original unstable nanopore, and the nanopore size can be finely tuned in situ at the nanoscale by simply adjusting the relative ratio of Fe3+ and TA monomers. Moreover, the hydrogen bonding interaction formed between the hydroxyl groups provided by TA and the phosphate groups of DNAs significantly increases the residence time of a short double-strand (100 bp) DNA. More importantly, we take advantage of the different strengths of hydrogen bonding interactions between the hydroxyl groups provided by TA and the analytes to discriminate between two oligonucleotide samples (oligodeoxycytidine and oligodeoxyadenosine) with similar sizes and lengths, of which the current signal patterns are significantly different using the coated nanopore. The results shed light on expanding the biochemical functionality of surface coatings on solid-state nanopores for future biomedical applications.
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Affiliation(s)
- Guanghao Wei
- State Key Lab for Mesoscopic Physics and Frontiers Science Center for Nano-Optoelectronics, School of Physics, Peking University, Beijing 100871, China
| | - Rui Hu
- State Key Lab for Mesoscopic Physics and Frontiers Science Center for Nano-Optoelectronics, School of Physics, Peking University, Beijing 100871, China
| | - Qiuhui Li
- State Key Lab for Mesoscopic Physics and Frontiers Science Center for Nano-Optoelectronics, School of Physics, Peking University, Beijing 100871, China
| | - Wenlong Lu
- State Key Lab for Mesoscopic Physics and Frontiers Science Center for Nano-Optoelectronics, School of Physics, Peking University, Beijing 100871, China
| | - Hanyu Liang
- The Cancer Hospital of the University of Chinese Academy of Sciences (Zhejiang Cancer Hospital), Institute of Basic Medicine and Cancer (IBMC), Chinese Academy of Sciences, Zhejiang, 310022 Hangzhou, China
| | - Hexin Nan
- The Cancer Hospital of the University of Chinese Academy of Sciences (Zhejiang Cancer Hospital), Institute of Basic Medicine and Cancer (IBMC), Chinese Academy of Sciences, Zhejiang, 310022 Hangzhou, China
| | - Jing Lu
- State Key Lab for Mesoscopic Physics and Frontiers Science Center for Nano-Optoelectronics, School of Physics, Peking University, Beijing 100871, China
- Peking University Yangtze Delta Institute of Optoelectronics, Nantong, 226010 Jiangsu, China
- Collaborative Innovation Center of Quantum Matter, Beijing 100084, China
| | - Juan Li
- The Cancer Hospital of the University of Chinese Academy of Sciences (Zhejiang Cancer Hospital), Institute of Basic Medicine and Cancer (IBMC), Chinese Academy of Sciences, Zhejiang, 310022 Hangzhou, China
| | - Qing Zhao
- State Key Lab for Mesoscopic Physics and Frontiers Science Center for Nano-Optoelectronics, School of Physics, Peking University, Beijing 100871, China
- Peking University Yangtze Delta Institute of Optoelectronics, Nantong, 226010 Jiangsu, China
- Collaborative Innovation Center of Quantum Matter, Beijing 100084, China
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Xu J, Li C, Shen Y, Zhu N. Anaerobic ammonium oxidation (anammox) promoted by pyrogenic biochar: Deciphering the interaction with extracellular polymeric substances (EPS). THE SCIENCE OF THE TOTAL ENVIRONMENT 2022; 802:149884. [PMID: 34464802 DOI: 10.1016/j.scitotenv.2021.149884] [Citation(s) in RCA: 24] [Impact Index Per Article: 12.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/08/2021] [Revised: 08/09/2021] [Accepted: 08/20/2021] [Indexed: 06/13/2023]
Abstract
Efficient biological nitrogen removal (BNR) by anaerobic ammonium oxidation (anammox) can be achieved with presence of redox-active pyrogenic biochar that potentially acting as an insoluble electron acceptor. Anammox bacteria and other symbiotic consortia are surrounded by extracellular polymeric substances (EPS) forming aggregate architecture, which also contains electrochemical-active biomolecules such as aromatic proteins and humic substances. Therefore, understanding the role of EPS is necessary in biochar-promoting anammox process. Herein, we investigated the influence of biochar with granular-sized (GP) and micrometer-sized (MP) particle sizes on microbiology and characteristics of EPS in anammox sludge. Addition of GP and MP biochar not only improved the BNR efficiency by 17.5% and 34.6%, respectively, but also increased the relative abundance of Candidatus Brocadia. The bulk and bound EPS contents substantially decreased in biochar-amended groups, while more slime EPS was produced. Spectroscopic (FTIR, Raman, and circular dichroism) and electrochemical (voltammetry and impedance spectrum) analyses revealed that biochar addition enhanced the structural integrity and electron-transfer capability of anammox sludge. EPS depletion led to a steep decrease in BNR efficiency (21.5% vs 83.0% with EPS-retained sludge), whereas it resumed to 42.1% in the presence of MP biochar. Electron transport system activity data showed that biochar replenished the loss of anaerobic respiration metabolism due to EPS depletion. In summary, these results suggested that EPS possibly work as transient mediator for shuttling electrons from ammonium oxidation to soluble (nitrite) and insoluble electron acceptors (redox-active biochar).
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Affiliation(s)
- Jiajia Xu
- School of Environmental Science and Engineering, Shanghai Jiao Tong University, Shanghai 200240, China; Shanghai Engineering Research Center of Solid Waste Treatment and Resource Recovery, Shanghai 200240, China
| | - Chao Li
- Hunan BISEN Environmental & Energy Co. Ltd, Changsha 410100, China
| | - Yanwen Shen
- School of Environmental Science and Engineering, Shanghai Jiao Tong University, Shanghai 200240, China; Hunan BISEN Environmental & Energy Co. Ltd, Changsha 410100, China; Shanghai Engineering Research Center of Solid Waste Treatment and Resource Recovery, Shanghai 200240, China.
| | - Nanwen Zhu
- School of Environmental Science and Engineering, Shanghai Jiao Tong University, Shanghai 200240, China; Shanghai Engineering Research Center of Solid Waste Treatment and Resource Recovery, Shanghai 200240, China
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Guo W, Zou X, Jiang H, Koebke KJ, Hoarau M, Crisci R, Lu T, Wei T, Marsh ENG, Chen Z. Molecular Structure of the Surface-Immobilized Super Uranyl Binding Protein. J Phys Chem B 2021; 125:7706-7716. [PMID: 34254804 DOI: 10.1021/acs.jpcb.1c03849] [Citation(s) in RCA: 17] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
Abstract
Recently, a super uranyl binding protein (SUP) was developed, which exhibits excellent sensitivity/selectivity to bind uranyl ions. It can be immobilized onto a surface in sensing devices to detect uranyl ions. Here, sum frequency generation (SFG) vibrational spectroscopy was applied to probe the interfacial structures of surface-immobilized SUP. The collected SFG spectra were compared to the calculated orientation-dependent SUP SFG spectra using a one-excitonic Hamiltonian approach based on the SUP crystal structures to deduce the most likely surface-immobilized SUP orientation(s). Furthermore, discrete molecular dynamics (DMD) simulation was applied to refine the surface-immobilized SUP conformations and orientations. The immobilized SUP structures calculated from DMD simulations confirmed the SUP orientations obtained from SFG data analyzed based on the crystal structures and were then used for a new round of SFG orientation analysis to more accurately determine the interfacial orientations and conformations of immobilized SUP before and after uranyl ion binding, providing an in-depth understanding of molecular interactions between SUP and the surface and the effect of uranyl ion binding on the SUP interfacial structures. We believe that the developed method of combining SFG measurements, DMD simulation, and Hamiltonian data analysis approach is widely applicable to study biomolecules at solid/liquid interfaces.
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Affiliation(s)
- Wen Guo
- Department of Chemistry, University of Michigan, 930 North University Avenue, Ann Arbor, Michigan 48109, United States
| | - Xingquan Zou
- Department of Chemistry, University of Michigan, 930 North University Avenue, Ann Arbor, Michigan 48109, United States
| | - Hanjie Jiang
- Department of Chemistry, University of Michigan, 930 North University Avenue, Ann Arbor, Michigan 48109, United States
| | - Karl J Koebke
- Department of Chemistry, University of Michigan, 930 North University Avenue, Ann Arbor, Michigan 48109, United States
| | - Marie Hoarau
- Department of Chemistry, University of Michigan, 930 North University Avenue, Ann Arbor, Michigan 48109, United States
| | - Ralph Crisci
- Department of Chemistry, University of Michigan, 930 North University Avenue, Ann Arbor, Michigan 48109, United States
| | - Tieyi Lu
- Department of Chemistry, University of Michigan, 930 North University Avenue, Ann Arbor, Michigan 48109, United States
| | - Tao Wei
- Department of Chemical Engineering, Howard University, 2366 Sixth Street, NW, Washington, D.C. 20059, United States
| | - E Neil G Marsh
- Department of Chemistry, University of Michigan, 930 North University Avenue, Ann Arbor, Michigan 48109, United States
| | - Zhan Chen
- Department of Chemistry, University of Michigan, 930 North University Avenue, Ann Arbor, Michigan 48109, United States
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9
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Karunanithy G, Shukla VK, Hansen DF. Methodological advancements for characterising protein side chains by NMR spectroscopy. Curr Opin Struct Biol 2021; 70:61-69. [PMID: 33989947 DOI: 10.1016/j.sbi.2021.04.002] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/17/2021] [Revised: 03/31/2021] [Accepted: 04/01/2021] [Indexed: 11/18/2022]
Abstract
The surface of proteins is covered by side chains of polar amino acids that are imperative for modulating protein functionality through the formation of noncovalent intermolecular interactions. However, despite their tremendous importance, the unique structures of protein side chains require tailored approaches for investigation by nuclear magnetic resonance spectroscopy and so have traditionally been understudied compared with the protein backbone. Here, we review substantial recent methodological advancements within nuclear magnetic resonance spectroscopy to address this issue. Specifically, we consider advancements that provide new insight into methyl-bearing side chains, show the potential of using non-natural amino acids and reveal the actions of charged side chains. Combined, the new methods promise unprecedented characterisations of side chains that will further elucidate protein function.
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Affiliation(s)
- Gogulan Karunanithy
- Department of Structural and Molecular Biology, Division of Biosciences, University College London, London, WC1E 6BT, United Kingdom
| | - Vaibhav Kumar Shukla
- Department of Structural and Molecular Biology, Division of Biosciences, University College London, London, WC1E 6BT, United Kingdom
| | - D Flemming Hansen
- Department of Structural and Molecular Biology, Division of Biosciences, University College London, London, WC1E 6BT, United Kingdom.
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Abstract
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Molecular association of proteins with nucleic
acids is required
for many biological processes essential to life. Electrostatic interactions
via ion pairs (salt bridges) of nucleic acid phosphates and protein
side chains are crucial for proteins to bind to DNA or RNA. Counterions
around the macromolecules are also key constituents for the thermodynamics
of protein–nucleic acid association. Until recently, there
had been only a limited amount of experiment-based information about
how ions and ionic moieties behave in biological macromolecular processes.
In the past decade, there has been significant progress in quantitative
experimental research on ionic interactions with nucleic acids and
their complexes with proteins. The highly negatively charged surfaces
of DNA and RNA electrostatically attract and condense cations, creating
a zone called the ion atmosphere. Recent experimental studies were
able to examine and validate theoretical models on ions and their
mobility and interactions with macromolecules. The ionic interactions
are highly dynamic. The counterions rapidly diffuse within the ion
atmosphere. Some of the ions are released from the ion atmosphere
when proteins bind to nucleic acids, balancing the charge via intermolecular
ion pairs of positively charged side chains and negatively charged
backbone phosphates. Previously, the release of counterions had been
implicated indirectly by the salt-concentration dependence of the
association constant. Recently, direct detection of counterion
release by NMR spectroscopy
has become possible and enabled more accurate and quantitative analysis
of the counterion release and its entropic impact on the thermodynamics
of protein–nucleic acid association. Recent studies also revealed
the dynamic nature of ion pairs of protein side chains and nucleic
acid phosphates. These ion pairs undergo transitions between two major
states. In one of the major states, the cation and the anion are in
direct contact and form hydrogen bonds. In the other major state,
the cation and the anion are separated by water. Transitions between
these states rapidly occur on a picosecond to nanosecond time scale.
When proteins interact with nucleic acids, interfacial arginine (Arg)
and lysine (Lys) side chains exhibit considerably different behaviors.
Arg side chains show a higher propensity to form rigid contacts with
nucleotide bases, whereas Lys side chains tend to be more mobile at
the molecular interfaces. The dynamic ionic interactions may facilitate
adaptive molecular recognition and play both thermodynamic and kinetic
roles in protein–nucleic acid interactions.
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Affiliation(s)
- Binhan Yu
- Department of Biochemistry & Molecular Biology, Sealy Center for Structural Biology & Molecular Biophysics, University of Texas Medical Branch, Galveston, Texas 77555-1068, United States
| | - B. Montgomery Pettitt
- Department of Biochemistry & Molecular Biology, Sealy Center for Structural Biology & Molecular Biophysics, University of Texas Medical Branch, Galveston, Texas 77555-1068, United States
| | - Junji Iwahara
- Department of Biochemistry & Molecular Biology, Sealy Center for Structural Biology & Molecular Biophysics, University of Texas Medical Branch, Galveston, Texas 77555-1068, United States
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Nepravishta R, Pletka CC, Iwahara J. Racemic phosphorothioate as a tool for NMR investigations of protein-DNA complexes. JOURNAL OF BIOMOLECULAR NMR 2020; 74:421-429. [PMID: 32683519 PMCID: PMC7511421 DOI: 10.1007/s10858-020-00333-x] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/06/2020] [Accepted: 07/09/2020] [Indexed: 05/05/2023]
Abstract
A major driving force for protein-nucleic acid association is electrostatic interactions via ion pairs of the positively charged basic side chains and negatively charged phosphates. For a better understanding of how proteins scan DNA and recognize particular signatures, it is important to gain atomic-level insight into the behavior of basic side chains at the protein-DNA interfaces. NMR spectroscopy is a powerful tool for investigating the structural, dynamic, and kinetic aspects of protein-DNA interactions. However, resonance assignment of basic side-chain cationic moieties at the molecular interfaces remains to be a major challenge. Here, we propose a fast, robust, and inexpensive approach that greatly facilitates resonance assignment of interfacial moieties and also allows for kinetic measurements of protein translocation between two DNA duplexes. This approach utilizes site-specific incorporation of racemic phosphorothioate at the position of a phosphate that interacts with a protein side chain. This modification retains the electric charge of phosphate and therefore is mild, but causes significant chemical shift perturbations for the proximal protein side chains, which facilitates resonance assignment. Due to the racemic nature of the modification, two different chemical shifts are observed for the species with different diastereomers RP and SP of the incorporated phosphorothioate group. Kinetic information on the exchange of the protein molecule between RP and SP DNA duplexes can be obtained by 15Nz exchange spectroscopy. We demonstrate the applications of this approach to the Antennapedia homeodomain-DNA complex and the CREB1 basic leucine-zipper (bZIP)-DNA complex.
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Affiliation(s)
- Ridvan Nepravishta
- Department of Biochemistry and Molecular Biology, Sealy Center for Structural Biology and Molecular Biophysics, University of Texas Medical Branch, Galveston, TX, 77555-1068, USA
| | - Channing C Pletka
- Department of Biochemistry and Molecular Biology, Sealy Center for Structural Biology and Molecular Biophysics, University of Texas Medical Branch, Galveston, TX, 77555-1068, USA
| | - Junji Iwahara
- Department of Biochemistry and Molecular Biology, Sealy Center for Structural Biology and Molecular Biophysics, University of Texas Medical Branch, Galveston, TX, 77555-1068, USA.
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