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Nirmalraj PN, Rossell MD, Dachraoui W, Thompson D, Mayer M. In Situ Observation of Chemically Induced Protein Denaturation at Solvated Interfaces. ACS APPLIED MATERIALS & INTERFACES 2023; 15:48015-48026. [PMID: 37797325 PMCID: PMC10591235 DOI: 10.1021/acsami.3c10510] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/24/2023] [Accepted: 09/22/2023] [Indexed: 10/07/2023]
Abstract
Proteins unfold in chaotropic salt solutions, a process that is difficult to observe at the single protein level. The work presented here demonstrates that a liquid-based atomic force microscope and graphene liquid-cell-based scanning transmission electron microscope make it possible to observe chemically induced protein unfolding. To illustrate this capability, ferritin proteins were deposited on a graphene surface, and the concentration-dependent urea- or guanidinium-induced changes of morphology were monitored for holo-ferritin with its ferrihydrite core as well as apo-ferritin without this core. Depending on the chaotropic agent the liquid-based imaging setup captured an unexpected transformation of natively folded holo-ferritin proteins into rings after urea treatment but not after guanidinium treatment. Urea treatment of apo-ferritin did not result in nanorings, confirming that nanorings are a specific signature of denaturation of holo-ferritins after exposture to sufficiently high urea concentrations. Mapping the in situ images with molecular dynamics simulations of ferritin subunits in urea solutions suggests that electrostatic destabilization triggers denaturation of ferritin as urea makes direct contact with the protein and also disrupts the water H-bonding network in the ferritin solvation shell. Our findings deepen the understanding of protein denaturation studied using label-free techniques operating at the solid-liquid interface.
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Affiliation(s)
- Peter Niraj Nirmalraj
- Transport
at Nanoscale Interfaces Laboratory, Swiss
Federal Laboratories for Materials Science and Technology, Überlandstrasse 129, 8600 Dübendorf, Switzerland
- Adolphe
Merkle Institute, University of Fribourg, Chemin des Verdiers 4, CH-1700 Fribourg, Switzerland
| | - Marta D. Rossell
- Electron
Microscopy Center, Swiss Federal Laboratories
for Materials Science and Technology, Überlandstrasse 129, 8600 Dübendorf, Switzerland
| | - Walid Dachraoui
- Electron
Microscopy Center, Swiss Federal Laboratories
for Materials Science and Technology, Überlandstrasse 129, 8600 Dübendorf, Switzerland
| | - Damien Thompson
- Department
of Physics, Bernal Institute, University
of Limerick, Limerick V94T9PX, Ireland
| | - Michael Mayer
- Adolphe
Merkle Institute, University of Fribourg, Chemin des Verdiers 4, CH-1700 Fribourg, Switzerland
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2
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Nakata N, Okamoto R, Sumi T, Koga K, Morita T, Imamura H. Molecular mechanism of the common and opposing cosolvent effects of fluorinated alcohol and urea on a coiled coil protein. Protein Sci 2023; 32:e4763. [PMID: 37622187 PMCID: PMC10519159 DOI: 10.1002/pro.4763] [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: 05/15/2023] [Revised: 08/07/2023] [Accepted: 08/21/2023] [Indexed: 08/26/2023]
Abstract
Alcohols and urea are widely used as effective protein denaturants. Among monohydric alcohols, 2,2,2-trifluoroethanol (TFE) has large cosolvent effects as a helix stabilizer in proteins. In contrast, urea efficiently denatures ordered native structures, including helices, into coils. These opposing cosolvent effects of TFE and urea are well known, even though both preferentially bind to proteins; however, the underlying molecular mechanism remains controversial. Cosolvent-dependent relative stability between native and denatured states is rigorously related to the difference in preferential binding parameters (PBPs) between these states. In this study, GCN4-p1 with two-stranded coiled coil helices was employed as a model protein, and molecular dynamics simulations for the helix dimer and isolated coil were conducted in aqueous solutions with 2 M TFE and urea. As 2 M cosolvent aqueous solutions did not exhibit clustering of cosolvent molecules, we were able to directly investigate the molecular origin of the excess PBP without considering the enhancement effect of PBPs arising from the concentration fluctuations. The calculated excess PBPs of TFE for the helices and those of urea for the coils were consistent with experimentally observed stabilization of helix by TFE and that of coil by urea. The former was caused by electrostatic interactions between TFE and side chains of the helices, while the latter was attributed to both electrostatic and dispersion interactions between urea and the main chains. Unexpectedly, reverse-micelle-like orientations of TFE molecules strengthened the electrostatic interactions between TFE and the side chains, resulting in strengthening of TFE solvation.
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Affiliation(s)
- Noa Nakata
- Department of Chemistry, Faculty of ScienceOkayama UniversityOkayamaJapan
| | - Ryuichi Okamoto
- Graduate School of Information Science, University of HyogoKobeHyogoJapan
| | - Tomonari Sumi
- Department of Chemistry, Faculty of ScienceOkayama UniversityOkayamaJapan
- Research Institute for Interdisciplinary Science, Okayama UniversityOkayamaJapan
| | - Kenichiro Koga
- Department of Chemistry, Faculty of ScienceOkayama UniversityOkayamaJapan
- Research Institute for Interdisciplinary Science, Okayama UniversityOkayamaJapan
| | - Takeshi Morita
- Department of ChemistryGraduate School of Science, Chiba UniversityChibaJapan
| | - Hiroshi Imamura
- Department of Bio‐ScienceNagahama Institute of Bio‐Science and TechnologyNagahamaShigaJapan
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3
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Feroz A, Khaki PSS, Bano B. Urea induced unfolding of rai seed cystatin: Influence of glycerol as a chemical chaperone. Colloids Surf B Biointerfaces 2023; 225:113233. [PMID: 36931044 DOI: 10.1016/j.colsurfb.2023.113233] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/15/2022] [Revised: 02/17/2023] [Accepted: 02/27/2023] [Indexed: 03/06/2023]
Abstract
Cystatin superfamily members, by virtue of their thiol protease regulatory properties, show involvement in myriad physiological processes important for survival and well-being. The current study involves urea-induced denaturation of a novel variant of the cystatin superfamily, rai seed cystatin (RSC), employing a variety of biophysical assays in order to characterize different folding intermediates generated on unfolding. Urea as a denaturant presented the passage of RSC through a series of events resulting in the loss of RSC functional capability, accompanied by changes in the archetype at secondary and tertiary structural levels, as evident from protease inhibitory, UV absorption, and intrinsic fluorescence assays, respectively. ANS fluorescence also revealed routing of RSC through discrete multiple sub-states thus presenting the generation of intermediate states somewhat close to the pre-molten globule and/or molten globule forms of RSC. Furthermore, far-UV circular dichroism analysis revealed a concentration-dependent gradual loss in typical -helical RSC peaks, indicating a nearly 50 % loss in secondary structural elements around 5 M urea treatment. The study also reports the possible role of glycerol in the refolding and/or reactivation of the urea unfolded RSC form. Glycerol presented itself as a potent structural stabilizer as it assisted in the refolding and reactivation of the unfolded RSC in a dosage-dependent manner, concomitantly paving the way for unravelling the mechanistic approach involved in the phenomenon, which can facilitate future studies.
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Affiliation(s)
- Anna Feroz
- Department of Biochemistry, Faculty of Life Sciences, AMU, Aligarh, UP, India; Department of Biosciences, Integral University, Lucknow, UP, India
| | | | - Bilqees Bano
- Department of Biochemistry, Faculty of Life Sciences, AMU, Aligarh, UP, India.
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Lee B, Lee JH, Kim DH, Kim ES, Seo BK, Rhyu IJ, Sun W. MAX: a simple, affordable, and rapid tissue clearing reagent for 3D imaging of wide variety of biological specimens. Sci Rep 2022; 12:19508. [PMID: 36376344 PMCID: PMC9663452 DOI: 10.1038/s41598-022-23376-6] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/25/2022] [Accepted: 10/31/2022] [Indexed: 11/15/2022] Open
Abstract
Transparency of biological specimens is crucial to obtaining detailed 3-dimensional images and understanding the structure and function of biological specimens. This transparency or tissue clearing can be achieved by adjusting the refractive index (RI) with embedding media and removing light barriers such as lipids, inorganic deposits, and pigments. Many currently available protocols consist of multiple steps to achieve sufficient transparency, making the process complex and time-consuming. Thus, in this study, we tailored the recipe for RI adjustment media named MAX based on the recently reported MACS protocol to achieve a single-step procedure, especially for ECM-rich tissues. This was achieved by the improvement of the tissue penetrability of the RI-matching reagent by combining MXDA with sucrose or iodixanol. While this was sufficient for the 3D imaging in many applications, MAX can also be combined with modular processes for de-lipidation, de-coloration, and de-calcification to further maximize the transparency depending on the special features of the tissues. Our approach provides an easy alternative for tissue clearing and 3D imaging.
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Affiliation(s)
- Boram Lee
- Department of Anatomy, Brain Korea 21 Plus Program for Biomedical Science, Korea University College of Medicine, Seoul, 02841, Republic of Korea
| | - Ju-Hyun Lee
- Department of Anatomy, Brain Korea 21 Plus Program for Biomedical Science, Korea University College of Medicine, Seoul, 02841, Republic of Korea
| | - Dai Hyun Kim
- Department of Anatomy, Brain Korea 21 Plus Program for Biomedical Science, Korea University College of Medicine, Seoul, 02841, Republic of Korea
- Department of Dermatology, Korea University College of Medicine, Seoul, 02841, Republic of Korea
| | - Eun Sil Kim
- Department of Radiology, Korea University Ansan Hospital, Korea University College of Medicine, Ansan, 15355, Republic of Korea
| | - Bo Kyoung Seo
- Department of Radiology, Korea University Ansan Hospital, Korea University College of Medicine, Ansan, 15355, Republic of Korea
| | - Im Joo Rhyu
- Department of Anatomy, Brain Korea 21 Plus Program for Biomedical Science, Korea University College of Medicine, Seoul, 02841, Republic of Korea
| | - Woong Sun
- Department of Anatomy, Brain Korea 21 Plus Program for Biomedical Science, Korea University College of Medicine, Seoul, 02841, Republic of Korea.
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Rojruthai P, Sakdapipanich J, Wiriyanantawong J, Ho CC, Chaiear N. Effect of Latex Purification and Accelerator Types on Rubber Allergens Prevalent in Sulphur Prevulcanized Natural Rubber Latex: Potential Application for Allergy-Free Natural Rubber Gloves. Polymers (Basel) 2022; 14:4679. [PMID: 36365670 PMCID: PMC9654386 DOI: 10.3390/polym14214679] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/30/2022] [Revised: 10/22/2022] [Accepted: 10/27/2022] [Indexed: 01/25/2024] Open
Abstract
Natural rubber (NR) gloves manufactured from NR latex are widely utilized in various applications as a personal protective device due to their exceptional barrier characteristics in infection control. However, the use of NR gloves was associated with concerns on NR protein allergy. With comprehensive leaching procedures now a common practice in NR latex glove factories to eliminate latent rubber proteins and chemical allergens, occurrences and complaints of protein allergy from medical glove users have decreased drastically over the past two decades. The present work aims to eliminate further the residual rubber allergens in NR latex through effective purification of the NR latex and compounding the thus purified latex with an established formulation for allergy-free NR for glove applications. NR latex was purified by deproteinization and saponification, respectively. Several analytical techniques were used to verify rubber allergens eliminated in the purified latexes. Saponified NR (SPNR) latex was the purified NR latex of choice since it is devoid of allergenic proteins and poses the lowest risk of Type I allergy. The purified NR latex was compounded with zinc diethyldithiocarbamate (ZDEC), zinc dibutyldithiocarbamate (ZDBC), and zinc 2-mercaptobenzothiazole (ZMBT), respectively, for glove dipping. Among the investigated accelerators, only ZDBC was not detected in the artificial sweat that came into contact with the dipped articles. Thus, it is deduced that ZDBC poses the lowest risk of Type IV allergy to consumers. Additionally, the morphological and physical properties of dipped articles were assessed. It was revealed that the dipped film from the SPNR latex compounded with ZDBC provided thinner and less yellow products with a more uniform internal structure and a tensile strength comparable to those of commercial NR gloves.
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Affiliation(s)
- Porntip Rojruthai
- Division of Chemical Industrial Process and Environment, Faculty of Science, Energy and Environment, King Mongkut’s University of Technology North Bangkok, Rayong 21120, Thailand
| | - Jitladda Sakdapipanich
- Department of Chemistry and Center of Excellence for Innovation in Chemistry (PERCH-CIC), Faculty of Science, Mahidol University, Salaya Campus, Phutthamonthon, Nakhon Pathom 73170, Thailand
| | - Jinjutha Wiriyanantawong
- Department of Chemistry and Center of Excellence for Innovation in Chemistry (PERCH-CIC), Faculty of Science, Mahidol University, Salaya Campus, Phutthamonthon, Nakhon Pathom 73170, Thailand
| | - Chee-Cheong Ho
- Sungai Long Campus, University Tunku Abdul Rahman, Cheras Kajang 43000, Malaysia
| | - Naesinee Chaiear
- Department of Community, Family and Occupational Medicine, Faculty of Medicine, Khon Kaen University, Khon Kaen 40002, Thailand
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Wang Q, Cui B, Guo L, Li Z, Chai Q, Wang N, Dong D, Nishinari K, Zhao M. The combined effects of NaCl-pH and urea-pH on the phase separation of type-A gelatin and dextran. Food Hydrocoll 2022. [DOI: 10.1016/j.foodhyd.2022.108287] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
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7
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Li Y, Liu M, Kong Y, Guo L, Yu X, Yu W, Shen J, Wen K, Wang Z. Significantly improved detection performances of immunoassay for ractopamine in urine based on highly urea-tolerant rabbit monoclonal antibody. Food Chem Toxicol 2022; 168:113358. [PMID: 35964837 DOI: 10.1016/j.fct.2022.113358] [Citation(s) in RCA: 5] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/02/2022] [Revised: 07/21/2022] [Accepted: 08/06/2022] [Indexed: 10/16/2022]
Abstract
Highly sensitive and accurate screening of ractopamine (RAC) residue in animal urine is greatly needed to ensure food security. The detection performance of immunoassay for RAC was always seriously harmed by the antibody inactivation derived from urea. Here, we first discovered one rabbit monoclonal antibody (RmAb) to RAC with a high affinity of 0.007 ng mL-1 and a surprising urea tolerance of 3 M urea, which is beneficial for developing robustly developed immunoassay in urine without sample pretreatment. The limits of detection of developed indirect competitive enzyme-linked immunosorbent assay based on RmAb1 for RAC were 0.0042-0.014 μg L-1 with the coefficient of variation below 11.7% in swine, sheep, and cow urine, significantly improved 10-100-fold in sensitivity. Moreover, the urea-tolerant mechanism of RmAb1 showed that more non-polar amino acids, more hydrogen bond donors on the surface, and preponderant Pi interaction of antibody-RAC all contributed to the stability of the RmAb1 in a high concentration of urea.
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Affiliation(s)
- Yuan Li
- Beijing Key Laboratory of Detection Technology for Animal-Derived Food Safety, Beijing Laboratory for Food Quality and Safety, College of Veterinary Medicine, China Agricultural University, 100193, Beijing, People's Republic of China
| | - Minggang Liu
- Beijing Key Laboratory of Detection Technology for Animal-Derived Food Safety, Beijing Laboratory for Food Quality and Safety, College of Veterinary Medicine, China Agricultural University, 100193, Beijing, People's Republic of China
| | - Yihui Kong
- Beijing Key Laboratory of Detection Technology for Animal-Derived Food Safety, Beijing Laboratory for Food Quality and Safety, College of Veterinary Medicine, China Agricultural University, 100193, Beijing, People's Republic of China
| | - Lina Guo
- Beijing Key Laboratory of Detection Technology for Animal-Derived Food Safety, Beijing Laboratory for Food Quality and Safety, College of Veterinary Medicine, China Agricultural University, 100193, Beijing, People's Republic of China
| | - Xuezhi Yu
- Beijing Key Laboratory of Detection Technology for Animal-Derived Food Safety, Beijing Laboratory for Food Quality and Safety, College of Veterinary Medicine, China Agricultural University, 100193, Beijing, People's Republic of China
| | - Wenbo Yu
- Beijing Key Laboratory of Detection Technology for Animal-Derived Food Safety, Beijing Laboratory for Food Quality and Safety, College of Veterinary Medicine, China Agricultural University, 100193, Beijing, People's Republic of China
| | - Jianzhong Shen
- Beijing Key Laboratory of Detection Technology for Animal-Derived Food Safety, Beijing Laboratory for Food Quality and Safety, College of Veterinary Medicine, China Agricultural University, 100193, Beijing, People's Republic of China
| | - Kai Wen
- Beijing Key Laboratory of Detection Technology for Animal-Derived Food Safety, Beijing Laboratory for Food Quality and Safety, College of Veterinary Medicine, China Agricultural University, 100193, Beijing, People's Republic of China
| | - Zhanhui Wang
- Beijing Key Laboratory of Detection Technology for Animal-Derived Food Safety, Beijing Laboratory for Food Quality and Safety, College of Veterinary Medicine, China Agricultural University, 100193, Beijing, People's Republic of China.
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8
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Huang Z, Sun J, Zhao L, He W, Liu T, Liu B. Analysis of the gel properties, microstructural characteristics, and intermolecular forces of soybean protein isolate gel induced by transglutaminase. Food Sci Nutr 2022; 10:772-783. [PMID: 35311166 PMCID: PMC8907741 DOI: 10.1002/fsn3.2706] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/20/2021] [Revised: 12/03/2021] [Accepted: 12/08/2021] [Indexed: 01/01/2023] Open
Abstract
Soybean protein isolate (SPI) is a high-quality plant protein that is primarily used to process various soybean products coagulated by transglutaminase (TGase). In this study, the degree of hydrolysis (DH), sulfhydryl content (SH), surface hydrophobicity (H0 ), secondary structural constitution, and microstructure of TGase-treated soybean protein (SPI, 7S, and 11S) were determined, as well as the effects of NaCl, urea, and SDS on the properties and intermolecular forces of SPI gel were analyzed. The results show that the H0 and SH content of SPI, 7S, and 11S decreased significantly with TGase treatment time (p < .05), while the DH gradually increased and reached its highest value (3.72%, 7.41%, and 1.27%, respectively) at 30 min. As the concentration of these two secondary structures exhibited an inverse relationship, the degradation of β-turns resulted in the increase in β-sheets. The microstructures of SPI and 11S gels were similar, being denser and more ordered than 7S gel. The low concentration of NaCl solution (0.2 mol/L) enhanced gel properties and intermolecular forces, promoting the formation of SPI gel, whereas a high concentration (0.4-0.8 mol/L) had a significant inhibitory effect. Urea and SDS solutions substantially inhibited the formation of SPI gel, leading to significant decreases in the water holding capacity and hardness as well as a considerable increase in the coagulation time (p < .05). The results revealed that hydrogen bonds and hydrophobic interactions were the main intermolecular forces responsible for the gel formation. This study provides adequate technical support and a theoretical basis for soybean protein gel products.
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Affiliation(s)
- Zhanrui Huang
- College of Food and Chemical EngineeringShaoyang UniversityHunan Provincial Key Laboratory of Soybean Products Processing and Safety ControlShaoyangChina
| | - Jing Sun
- College of Food and Chemical EngineeringShaoyang UniversityHunan Provincial Key Laboratory of Soybean Products Processing and Safety ControlShaoyangChina
| | - Liangzhong Zhao
- College of Food and Chemical EngineeringShaoyang UniversityHunan Provincial Key Laboratory of Soybean Products Processing and Safety ControlShaoyangChina
| | - Wanying He
- College of Food and Chemical EngineeringShaoyang UniversityHunan Provincial Key Laboratory of Soybean Products Processing and Safety ControlShaoyangChina
| | - Teyuan Liu
- Jinzai Food Group Co., Ltd.YueyangChina
- Pingjiang Jinzai Food Co., LtdYueyangChina
| | - Binbin Liu
- Jinzai Food Group Co., Ltd.YueyangChina
- Pingjiang Jinzai Food Co., LtdYueyangChina
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Shahebrahimi Y, Fazlali A. Phase equilibria, physical and rheological properties of extracellular polymeric substances in the aqueous urea solutions at different temperatures and concentrations. JOURNAL OF ENVIRONMENTAL MANAGEMENT 2021; 284:112103. [PMID: 33567355 DOI: 10.1016/j.jenvman.2021.112103] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/13/2020] [Revised: 01/17/2021] [Accepted: 01/30/2021] [Indexed: 06/12/2023]
Abstract
Extracellular polymeric substances (EPS) were extracted from aerobic granule sludge (AGS) using 8 M aqueous urea solution. It seems that the knowledge of these multi-component systems properties and the ability to predict their phase behavior is necessary for the extraction units design as well as process optimization. In this regard, water activity using the Dynamic Vapor Sorption (DVS) method, viscosity and shear stress, pH, and conductivity were measured at 283.15-343.15 K and 0.0108 to 0.0375 wt fraction of EPS. The salting effects in ternary systems assessed and the results were interpreted in terms of solute-water and solute-solute interactions. It was found these systems were not semi-ideal and except at 283.15 K, had a positive deviation from ideal solution behavior and only at this temperature as the optimum extraction temperature, the salting-in effect was observed for each concentration of EPS. The ternary solutions behave like pseudo-plastic fluids while aqueous urea solution is a Newtonian fluid. Increasing the temperature causes a decrease and increase in pH and conductivity of ternary solutions, respectively and the presence of EPS increases those of 8 M urea solution significantly.
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Affiliation(s)
- Yasaman Shahebrahimi
- Department of Chemical Engineering, Faculty of Engineering, Arak University, Arak, 38156879, Iran.
| | - Alireza Fazlali
- Department of Chemical Engineering, Faculty of Engineering, Arak University, Arak, 38156879, Iran
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Thermodynamic analysis of proton- and urea-induced dissociation of tobacco mosaic virus: stoichiometry, common ion effect, cooperativity, heterogeneity of subunits and the effect of urea as a homogenizer. CHEMICAL PAPERS 2020. [DOI: 10.1007/s11696-020-01125-1] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/24/2022]
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11
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Raghunathan S, Jaganade T, Priyakumar UD. Urea-aromatic interactions in biology. Biophys Rev 2020; 12:65-84. [PMID: 32067192 PMCID: PMC7040157 DOI: 10.1007/s12551-020-00620-9] [Citation(s) in RCA: 13] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/05/2019] [Accepted: 01/08/2020] [Indexed: 02/06/2023] Open
Abstract
Noncovalent interactions are key determinants in both chemical and biological processes. Among such processes, the hydrophobic interactions play an eminent role in folding of proteins, nucleic acids, formation of membranes, protein-ligand recognition, etc.. Though this interaction is mediated through the aqueous solvent, the stability of the above biomolecules can be highly sensitive to any small external perturbations, such as temperature, pressure, pH, or even cosolvent additives, like, urea-a highly soluble small organic molecule utilized by various living organisms to regulate osmotic pressure. A plethora of detailed studies exist covering both experimental and theoretical regimes, to understand how urea modulates the stability of biological macromolecules. While experimentalists have been primarily focusing on the thermodynamic and kinetic aspects, theoretical modeling predominantly involves mechanistic information at the molecular level, calculating atomistic details applying the force field approach to the high level electronic details using the quantum mechanical methods. The review focuses mainly on examples with biological relevance, such as (1) urea-assisted protein unfolding, (2) urea-assisted RNA unfolding, (3) urea lesion interaction within damaged DNA, (4) urea conduction through membrane proteins, and (5) protein-ligand interactions those explicitly address the vitality of hydrophobic interactions involving exclusively the urea-aromatic moiety.
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Affiliation(s)
- Shampa Raghunathan
- Center for Computational Natural Sciences and Bioinformatics, International Institute of Information Technology, Hyderabad, 500032, India
| | - Tanashree Jaganade
- Center for Computational Natural Sciences and Bioinformatics, International Institute of Information Technology, Hyderabad, 500032, India
| | - U Deva Priyakumar
- Center for Computational Natural Sciences and Bioinformatics, International Institute of Information Technology, Hyderabad, 500032, India.
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12
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Su Z, Dias CL. Individual and combined effects of urea and trimethylamine N-oxide (TMAO) on protein structures. J Mol Liq 2019. [DOI: 10.1016/j.molliq.2019.111443] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
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13
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Elbahnasawy MA, Farag MMS, Mansour MT, El-Ghamery AA. Cloning, expression and nanodiscs assemble of recombinant HIV-1 gp41. Microb Pathog 2019; 138:103824. [PMID: 31669502 DOI: 10.1016/j.micpath.2019.103824] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/29/2019] [Revised: 10/23/2019] [Accepted: 10/24/2019] [Indexed: 02/06/2023]
Abstract
Structural studies of membrane proteins have been hurdled by their difficulty for expression in heterogeneous expression systems due to their intrinsically strong hydrophobicity and requirements for association with other cellular membranes. This study aims to design a construct for expression of membrane proteins. Because of its outstanding interest in HIV-1 vaccine design, transmembrane gp41 amino acid residue 662-723 was chosen as a representative membrane protein. Therefore, we constructed expression vectors for expression of gp41(662-723) alone (pET28a-gp41(662-723)) or coupled with a fusion partner: GB1 (pET30a-GB1-gp41(662-723)) and Trx (pET32a-Trx-gp41(662-723)). For enhancing protein expression, the expression plasmids were transformed into E. coli BL-21 (DE3), E. coli T7 Express lysY/Iq and E. coli Lemo21 (DE3). Interestingly, HIV-1 gp41(662-723) was expressed as a C-terminus fusion to the fusion partner Trx (Trx-gp41(662-723)) with an apparent molecular mass of 21.8 kDa. Trx-gp41(662-723) was overexpressed into E. coli T7 Express lysY/Iq by early induction as OD600 ~0.5 followed by incubation at 20 °C/overnight. Our data demonstrated that almost all recombinant Trx-gp41(662-723) was incorporated into lipid nanodiscs by slowing down the nanodiscs assembly process. Negative-stained electron micrographs revealed homogenous 10 nm Trx-gp41(662-723)-nanodiscs. While the neutralizing epitopes in the purified Trx-gp41(662-723) were accessible and recognizable by anti-MPER bNAbs, these epitopes became less accessibly exposed, particularly in the C-terminal region of MPER, after incorporation of Trx-gp41(662-723) into nanodiscs.
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Affiliation(s)
- Mostafa A Elbahnasawy
- Laboratory of Immunobiology and Department of Medical Oncology, Dana-Farber Cancer Institute, Boston, MA, 02115, USA; Immunology Lab, Botany and Microbiology Department, Faculty of Science, Al-Azhar University, Nasr City, Cairo, 11884, Egypt.
| | - Mohamed M S Farag
- Immunology Lab, Botany and Microbiology Department, Faculty of Science, Al-Azhar University, Nasr City, Cairo, 11884, Egypt.
| | - Mohamed T Mansour
- Molecular Virology Lab, Children's Cancer Hospital Egypt-57357, NCI, Cairo university, Cairo, 11562, Egypt
| | - Abbas A El-Ghamery
- Cytology Lab, Botany and Microbiology Department, Faculty of Science, Al-Azhar University, Nasr City, Cairo, 11884, Egypt
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Sethuraman S, Rajendran K. Is Gum Arabic a Good Emulsifier Due to CH...π Interactions? How Urea Effectively Destabilizes the Hydrophobic CH...π Interactions in the Proteins of Gum Arabic than Amides and GuHCl? ACS OMEGA 2019; 4:16418-16428. [PMID: 31616820 PMCID: PMC6787882 DOI: 10.1021/acsomega.9b01980] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/01/2019] [Accepted: 09/11/2019] [Indexed: 05/13/2023]
Abstract
The photophysical studies of gum arabic (GA) in the presence of urea, 1,3-dimethylurea (DMU), tetramethylurea (TMU), guanidine hydrochloride (GuHCl), formamide (FA), acetamide (AA), and dimethyl formamide (DMF) were carried out by monitoring the emission, three-dimensional emission contour, and time-correlated fluorescence lifetime techniques. On addition of only 1 × 10-3 M urea, 75.0% of the fluorescence of GA is quenched, while the same occurs in GuHCl at 3.0 M. FA quenched 50% of the fluorescence of GA at 5.0 M. However, DMU, TMU, AA, and DMF resulted in a fluorescence enhancement. The unusual fluorescence trends reveal the existence of CH...π interactions in the proteins of GA. The experimental results and the structural aspects of proteins in GA led us to propose that the aggregation of polyproline helices in GA, through several CH...π interactions, would have a major role to play in the emulsification mechanism of GA.
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Affiliation(s)
- Sowmiya Sethuraman
- Department of Chemistry, D.G. Vaishnav College, Autonomous (affiliated to the
University of Madras (Chennai)), 833, Periyar EVR Salai, Arumbakkam, Chennai 600 106, Tamil Nadu, India
| | - Kumaran Rajendran
- Department of Chemistry, D.G. Vaishnav College, Autonomous (affiliated to the
University of Madras (Chennai)), 833, Periyar EVR Salai, Arumbakkam, Chennai 600 106, Tamil Nadu, India
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15
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Sanawar H, Pinel I, Farhat N, Bucs S, Zlopasa J, Kruithof J, Witkamp G, van Loosdrecht M, Vrouwenvelder J. Enhanced biofilm solubilization by urea in reverse osmosis membrane systems. WATER RESEARCH X 2018; 1:100004. [PMID: 31194008 PMCID: PMC6549900 DOI: 10.1016/j.wroa.2018.10.001] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/26/2018] [Revised: 10/04/2018] [Accepted: 10/11/2018] [Indexed: 05/24/2023]
Abstract
Chemical cleaning is routinely performed in reverse osmosis (RO) plants for the regeneration of RO membranes that suffer from biofouling problems. The potential of urea as a chaotropic agent to enhance the solubilization of biofilm proteins has been reported briefly in the literature. In this paper the efficiency of urea cleaning for RO membrane systems has been compared to conventionally applied acid/alkali treatment. Preliminary assessment confirmed that urea did not damage the RO polyamide membranes and that the membrane cleaning efficiency increased with increasing concentrations of urea and temperature. Accelerated biofilm formation was carried out in membrane fouling simulators which were subsequently cleaned with (i) 0.01M sodium hydroxide (NaOH) and 0.1M hydrochloric acid (HCl) (typically applied in industry), (ii) urea (CO(NH2)2) and hydrochloric acid, or (iii) urea only (1340 g/Lwater). The pressure drop over the flow channel was used to evaluate the efficiency of the applied chemical cleanings. Biomass removal was evaluated by measuring chemical oxygen demand (COD), adenosine triphosphate (ATP), protein, and carbohydrate content from the membrane and spacer surfaces after cleaning. In addition to protein and carbohydrate quantification of the extracellular polymeric substances (EPS), fluorescence excitation-emission matrix (FEEM) spectroscopy was used to distinguish the difference in organic matter of the remaining biomass to assess biofilm solubilization efficacy of the different cleaning agents. Results indicated that two-stage CO(NH2)2/HCl cleaning was as effective as cleaning with NaOH/HCl in terms of restoring the feed channel pressure drop (>70% pressure drop decrease). One-stage cleaning with urea only was not as effective indicating the importance of the second-stage low pH acid cleaning in weakening the biofilm matrix. All three chemical cleaning protocols were equally effective in reducing the concentration of predominant EPS components protein and carbohydrate (>50% reduction in concentrations). However, urea-based cleaning strategies were more effective in solubilizing protein-like matter and tyrosine-containing proteins. Furthermore, ATP measurements showed that biomass inactivation was up to two-fold greater after treatment with urea-based chemical cleanings compared to the conventional acid/alkali treatment. The applicability of urea as an alternative, economical, eco-friendly and effective chemical cleaning agent for the control of biological fouling was successfully demonstrated.
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Affiliation(s)
- H. Sanawar
- King Abdullah University of Science and Technology (KAUST), Water Desalination and Reuse Center (WDRC), Division of Biological and Environmental Science and Engineering (BESE), Thuwal, 23955-6900, Saudi Arabia
| | - I. Pinel
- Department of Biotechnology, Faculty of Applied Sciences, Delft University of Technology, Van der Maasweg 9, 2629, HZ Delft, the Netherlands
| | - N.M. Farhat
- King Abdullah University of Science and Technology (KAUST), Water Desalination and Reuse Center (WDRC), Division of Biological and Environmental Science and Engineering (BESE), Thuwal, 23955-6900, Saudi Arabia
| | - Sz.S. Bucs
- King Abdullah University of Science and Technology (KAUST), Water Desalination and Reuse Center (WDRC), Division of Biological and Environmental Science and Engineering (BESE), Thuwal, 23955-6900, Saudi Arabia
| | - J. Zlopasa
- Department of Biotechnology, Faculty of Applied Sciences, Delft University of Technology, Van der Maasweg 9, 2629, HZ Delft, the Netherlands
| | - J.C. Kruithof
- Wetsus, European Centre of Excellence for Sustainable Water Technology, Oostergoweg 9, 8911, MA, Leeuwarden, the Netherlands
| | - G.J. Witkamp
- King Abdullah University of Science and Technology (KAUST), Water Desalination and Reuse Center (WDRC), Division of Biological and Environmental Science and Engineering (BESE), Thuwal, 23955-6900, Saudi Arabia
- Department of Biotechnology, Faculty of Applied Sciences, Delft University of Technology, Van der Maasweg 9, 2629, HZ Delft, the Netherlands
| | - M.C.M. van Loosdrecht
- Department of Biotechnology, Faculty of Applied Sciences, Delft University of Technology, Van der Maasweg 9, 2629, HZ Delft, the Netherlands
| | - J.S. Vrouwenvelder
- King Abdullah University of Science and Technology (KAUST), Water Desalination and Reuse Center (WDRC), Division of Biological and Environmental Science and Engineering (BESE), Thuwal, 23955-6900, Saudi Arabia
- Department of Biotechnology, Faculty of Applied Sciences, Delft University of Technology, Van der Maasweg 9, 2629, HZ Delft, the Netherlands
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16
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Peng P, Zhang P, Ma H, Zhai C. Hydrogen Bond Interaction of Ascorbic Acid with Urea: Experimental and Theoretical Study. Z PHYS CHEM 2018. [DOI: 10.1515/zpch-2018-1177] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022]
Abstract
Abstract
The interactions of ascorbic acid (AA) with urea were investigated by using the cyclic voltammetry, density functional theory, atoms in molecules and natural bond orbital analyses. The experimental and theoretical results show that the hydrogen bonds are formed between AA and urea, wherein the mainly interaction sites are the hydrogen atoms on enediol of AA and the oxygen atom on carbonyl of urea. The electrochemical behavior of AA was significantly affected by above interactions.
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Affiliation(s)
- Peng Peng
- Institute of Functional Polymer Composites, College of Chemistry and Chemical Engineering , Henan University , Kaifeng, 475004 , China
| | - Ping Zhang
- Institute of Functional Polymer Composites, College of Chemistry and Chemical Engineering , Henan University , Kaifeng, 475004 , China
| | - Huiting Ma
- Institute of Functional Polymer Composites, College of Chemistry and Chemical Engineering , Henan University , Kaifeng, 475004 , China
| | - Cuiping Zhai
- Institute of Functional Polymer Composites, College of Chemistry and Chemical Engineering , Henan University , Kaifeng, 475004 , China , Tel.: +86 037123881589, Fax: 86 037123881589
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17
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Su Z, Ravindhran G, Dias CL. Effects of Trimethylamine-N-oxide (TMAO) on Hydrophobic and Charged Interactions. J Phys Chem B 2018; 122:5557-5566. [DOI: 10.1021/acs.jpcb.7b11847] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Affiliation(s)
- Zhaoqian Su
- Department of Physics, New Jersey Institute of Technology, University Heights Newark, New Jersey 07102-1982, United States
| | - Gopal Ravindhran
- Department of Physics, New Jersey Institute of Technology, University Heights Newark, New Jersey 07102-1982, United States
| | - Cristiano L. Dias
- Department of Physics, New Jersey Institute of Technology, University Heights Newark, New Jersey 07102-1982, United States
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18
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Meti MD, Dixit MK, Tembe BL. Salting-in of neopentane in the aqueous solutions of urea and glycine-betaine. MOLECULAR SIMULATION 2018. [DOI: 10.1080/08927022.2018.1431834] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
Affiliation(s)
- Manjunath D. Meti
- Department of Chemistry, Indian Institute of Technology Bombay, Powai, Mumbai, India
| | - Mayank K. Dixit
- Department of Chemistry, Indian Institute of Technology Bombay, Powai, Mumbai, India
| | - Bhalachandra L. Tembe
- Department of Chemistry, Indian Institute of Technology Bombay, Powai, Mumbai, India
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19
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The opposing effect of urea and high pressure on the conformation of the protein β-hairpin: A molecular dynamics simulation study. J Mol Liq 2018. [DOI: 10.1016/j.molliq.2017.12.054] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
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20
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Niether D, Di Lecce S, Bresme F, Wiegand S. Unravelling the hydrophobicity of urea in water using thermodiffusion: implications for protein denaturation. Phys Chem Chem Phys 2018; 20:1012-1020. [DOI: 10.1039/c7cp05843h] [Citation(s) in RCA: 19] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Sensitivity of thermodiffusion to urea–water interactions was studied experimentally and by NEMD simulations, identifying the hydrophobic behaviour of urea.
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Affiliation(s)
- Doreen Niether
- ICS-3 Soft Condensed Matter
- Forschungszentrum Jülich GmbH
- D-52428 Jülich
- Germany
| | | | - Fernando Bresme
- Department of Chemistry
- Imperial College
- London SW7 2AZ
- UK
- Department of Chemistry
| | - Simone Wiegand
- ICS-3 Soft Condensed Matter
- Forschungszentrum Jülich GmbH
- D-52428 Jülich
- Germany
- Department für Chemie-Physikalische Chemie
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21
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Zhang C, Yang M, Zhao K. Insight into the effect mechanism of urea-induced protein denaturation by dielectric spectroscopy. Phys Chem Chem Phys 2017; 19:32007-32015. [PMID: 29177311 DOI: 10.1039/c7cp05994a] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Dielectric relaxation spectroscopy was applied to study how urea affects the phase transition of a thermosensitive polymer, poly(N-isopropylacrylamide) (PNIPAM), which has been widely used as a protein model. It was found that there is a pronounced relaxation near 10 GHz for the ternary system of PNIPAM in urea aqueous solution. The temperature dependence of dielectric parameters indicates that urea can reduce the lower critical solution temperature (LCST) of PNIPAM, i.e., stabilize the globule state of PNIPAM and collapse the PNIPAM chains. Based on our results, the interaction mechanism of urea on the conformational transition of PNIPAM was presented: urea replaces water molecules directly bonding with PNIPAM and acts as the bridging agent for the adjacent side chains of PNIPAM. Accordingly, the mechanism with which urea denatures protein was deduced. In addition, it is worth mentioning that, from the temperature dependence of the dielectric parameters obtained in the presence of urea, an interesting phenomenon was found in which the effect of urea on PNIPAM seems to take 2 M as a unit. This result may be the reason why urea and TMAO exit marine fishes at a specific ratio of 2 : 1.
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Affiliation(s)
- Cancan Zhang
- College of Chemistry, Beijing Normal University, Beijing 100875, China.
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22
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de Oliveira GA, Silva JL. The push-and-pull hypothesis in protein unfolding, misfolding and aggregation. Biophys Chem 2017; 231:20-26. [DOI: 10.1016/j.bpc.2017.03.007] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/14/2017] [Revised: 03/25/2017] [Accepted: 03/27/2017] [Indexed: 01/17/2023]
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23
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Su Z, Mahmoudinobar F, Dias CL. Effects of Trimethylamine-N-oxide on the Conformation of Peptides and its Implications for Proteins. PHYSICAL REVIEW LETTERS 2017; 119:108102. [PMID: 28949191 DOI: 10.1103/physrevlett.119.108102] [Citation(s) in RCA: 42] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/23/2017] [Indexed: 05/16/2023]
Abstract
To provide insights into the stabilizing mechanisms of trimethylamine-N-oxide (TMAO) on protein structures, we perform all-atom molecular dynamics simulations of peptides and the Trp-cage miniprotein. The effects of TMAO on the backbone and charged residues of peptides are found to stabilize compact conformations, whereas effects of TMAO on nonpolar residues lead to peptide swelling. This suggests competing mechanisms of TMAO on proteins, which accounts for hydrophobic swelling, backbone collapse, and stabilization of charge-charge interactions. These mechanisms are observed in Trp cage.
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Affiliation(s)
- Zhaoqian Su
- Physics Department, New Jersey Institute of Technology, Newark, 07102-1982 New Jersey, USA
| | - Farbod Mahmoudinobar
- Physics Department, New Jersey Institute of Technology, Newark, 07102-1982 New Jersey, USA
| | - Cristiano L Dias
- Physics Department, New Jersey Institute of Technology, Newark, 07102-1982 New Jersey, USA
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24
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Ashraf Kharaz Y, Zamboulis D, Sanders K, Comerford E, Clegg P, Peffers M. Comparison between chaotropic and detergent-based sample preparation workflow in tendon for mass spectrometry analysis. Proteomics 2017; 17:1700018. [PMID: 28547889 PMCID: PMC5575552 DOI: 10.1002/pmic.201700018] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/13/2017] [Revised: 05/16/2017] [Accepted: 05/19/2017] [Indexed: 01/12/2023]
Abstract
Exploring the tendon proteome is a challenging but important task for understanding the mechanisms of physiological/pathological processes during ageing and disease and for the development of new treatments. Several extraction methods have been utilised for tendon mass spectrometry, however different extraction methods have not been simultaneously compared. In the present study we compared protein extraction in tendon with two chaotropic agents, guanidine hydrochloride (GnHCl) and urea, a detergent, RapiGest™, and their combinations for shotgun mass spectrometry. An initial proteomic analysis was performed following urea, GnHCl, and RapiGest™ extraction of equine superficial digital flexor tendon (SDFT) tissue. Subsequently, another proteomic analysis was performed following extraction with GnHCl, Rapigest™, and their combinations. Between the two chaotropic agents, GnHCl extracted more proteins, whilst a greater number of proteins were solely identified after Rapigest™ extraction. Protein extraction with a combination of GnHCl followed by RapiGest™ on the insoluble pellet demonstrated, after label-free quantification, increased abundance of identified collagen proteins and low sample to sample variability. In contrast, GnHCl extraction on its own showed increased abundance of identified proteoglycans and cellular proteins. Therefore, the selection of protein extraction method for tendon tissue for mass spectrometry analysis should reflect the focus of the study.
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Affiliation(s)
- Yalda Ashraf Kharaz
- Department of Musculoskeletal Biology, Institute of Ageing and Chronic DiseaseUniversity of LiverpoolLiverpoolUK
| | - Danae Zamboulis
- Department of Musculoskeletal Biology, Institute of Ageing and Chronic DiseaseUniversity of LiverpoolLiverpoolUK
| | - Karen Sanders
- Department of Musculoskeletal Biology, Institute of Ageing and Chronic DiseaseUniversity of LiverpoolLiverpoolUK
| | - Eithne Comerford
- Department of Musculoskeletal Biology, Institute of Ageing and Chronic DiseaseUniversity of LiverpoolLiverpoolUK
| | - Peter Clegg
- Department of Musculoskeletal Biology, Institute of Ageing and Chronic DiseaseUniversity of LiverpoolLiverpoolUK
- The MRC‐Arthritis Research UK Centre for Integrated research into Musculoskeletal Ageing (CIMA)LiverpoolUK
| | - Mandy Peffers
- Department of Musculoskeletal Biology, Institute of Ageing and Chronic DiseaseUniversity of LiverpoolLiverpoolUK
- The MRC‐Arthritis Research UK Centre for Integrated research into Musculoskeletal Ageing (CIMA)LiverpoolUK
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25
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Steinke N, Genina A, Lorenz CD, McLain SE. Salt Interactions in Solution Prevent Direct Association of Urea with a Peptide Backbone. J Phys Chem B 2017; 121:1866-1876. [DOI: 10.1021/acs.jpcb.6b12542] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Affiliation(s)
- Nicola Steinke
- Department of Biochemistry, University of Oxford, Oxford OX1 3QU, U.K
| | - Anna Genina
- Department of Physics, King’s College London, London SE1 9NH, U.K
| | | | - Sylvia E. McLain
- Department of Biochemistry, University of Oxford, Oxford OX1 3QU, U.K
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