1
|
Abstract
Glycans, carbohydrate molecules in the realm of biology, are present as biomedically important glycoconjugates and a characteristic aspect is that their structures in many instances are branched. In determining the primary structure of a glycan, the sugar components including the absolute configuration and ring form, anomeric configuration, linkage(s), sequence, and substituents should be elucidated. Solution state NMR spectroscopy offers a unique opportunity to resolve all these aspects at atomic resolution. During the last two decades, advancement of both NMR experiments and spectrometer hardware have made it possible to unravel carbohydrate structure more efficiently. These developments applicable to glycans include, inter alia, NMR experiments that reduce spectral overlap, use selective excitations, record tilted projections of multidimensional spectra, acquire spectra by multiple receivers, utilize polarization by fast-pulsing techniques, concatenate pulse-sequence modules to acquire several spectra in a single measurement, acquire pure shift correlated spectra devoid of scalar couplings, employ stable isotope labeling to efficiently obtain homo- and/or heteronuclear correlations, as well as those that rely on dipolar cross-correlated interactions for sequential information. Refined computer programs for NMR spin simulation and chemical shift prediction aid the structural elucidation of glycans, which are notorious for their limited spectral dispersion. Hardware developments include cryogenically cold probes and dynamic nuclear polarization techniques, both resulting in enhanced sensitivity as well as ultrahigh field NMR spectrometers with a 1H NMR resonance frequency higher than 1 GHz, thus improving resolution of resonances. Taken together, the developments have made and will in the future make it possible to elucidate carbohydrate structure in great detail, thereby forming the basis for understanding of how glycans interact with other molecules.
Collapse
Affiliation(s)
- Carolina Fontana
- Departamento
de Química del Litoral, CENUR Litoral Norte, Universidad de la República, Paysandú 60000, Uruguay
| | - Göran Widmalm
- Department
of Organic Chemistry, Arrhenius Laboratory, Stockholm University, S-106 91 Stockholm, Sweden
| |
Collapse
|
2
|
Xue Y, Nestor G. Determination of Amide Cis/Trans Isomers in N-Acetyl-d-glucosamine: Tailored NMR Analysis of the N-Acetyl Group Conformation. Chembiochem 2022; 23:e202200338. [PMID: 35713405 PMCID: PMC9541821 DOI: 10.1002/cbic.202200338] [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: 06/14/2022] [Revised: 06/17/2022] [Indexed: 11/14/2022]
Abstract
N‐Acetyl‐d‐glucosamine (GlcNAc) is one of the most common amino sugars in nature, but the conformation of its N‐acetyl group has drawn little attention. We report herein the first identification of NH protons of the amide cis forms of α‐ and β‐GlcNAc by NMR spectroscopy. Relative quantification and thermodynamic analysis of both cis and trans forms was carried out in aqueous solution. The NH protons were further utilized by adapting protein NMR experiments to measure eight J‐couplings within the N‐acetyl group, of which six are sensitive to the H2‐NH conformation and two are sensitive to the amide conformation. For amide cis and trans forms, the orientation between H2 and NH was determined as anti conformation, while a small percentage of syn conformation was predicted for the amide trans form of β‐GlcNAc. This approach holds great promise for the detailed conformational analysis of GlcNAc in larger biomolecules, such as glycoproteins and polysaccharides.
Collapse
Affiliation(s)
- Yan Xue
- Swedish University of Agricultural Sciences: Sveriges lantbruksuniversitet, Department of Molecular Sciences, SWEDEN
| | - Gustav Nestor
- Swedish University of Agricultural Sciences, Department of Molecular Sciences, Almas allé 5, Box 7015, 750 07, Uppsala, SWEDEN
| |
Collapse
|
3
|
Methods for Measuring Exchangeable Protons in Glycosaminoglycans. Methods Mol Biol 2021. [PMID: 34626393 DOI: 10.1007/978-1-0716-1398-6_29] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register]
Abstract
Recent NMR studies of the exchangeable protons of GAGs in aqueous solution, including those of the amide, sulfamate, and hydroxyl moieties, have demonstrated potential for the detection of intramolecular hydrogen bonds providing insights into secondary structure preferences. GAG amide protons are observable by NMR over wide pH and temperature ranges; however, specific solution conditions are required to reduce the exchange rate of the sulfamate and hydroxyl protons and allow their detection by NMR. Building on the vast body of knowledge on detection of hydrogen bonds in peptides and proteins, a variety of methods can be used to identify hydrogen bonds in GAGs including temperature coefficient measurements, evaluation of chemical shift differences between oligo- and monosaccharides, and relative exchange rates measured through line shape analysis and EXSY spectra. Emerging strategies to allow direct detection of hydrogen bonds through heteronuclear couplings offer promise for the future. Molecular dynamic simulations are important in this effort both to predict and confirm hydrogen bond donors and acceptors.
Collapse
|
4
|
Nesměrák K, Pospíchal R. Spectrometric methods in pharmaceutical analysis of glycosaminoglycans: the state-of-the-art. MONATSHEFTE FUR CHEMIE 2020. [DOI: 10.1007/s00706-020-02632-3] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/24/2022]
|
5
|
Devlin A, Mycroft-West C, Procter P, Cooper L, Guimond S, Lima M, Yates E, Skidmore M. Tools for the Quality Control of Pharmaceutical Heparin. MEDICINA (KAUNAS, LITHUANIA) 2019; 55:E636. [PMID: 31557911 PMCID: PMC6843833 DOI: 10.3390/medicina55100636] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 06/30/2019] [Revised: 09/02/2019] [Accepted: 09/04/2019] [Indexed: 11/25/2022]
Abstract
Heparin is a vital pharmaceutical anticoagulant drug and remains one of the few naturally sourced pharmaceutical agents used clinically. Heparin possesses a structural order with up to four levels of complexity. These levels are subject to change based on the animal or even tissue sources that they are extracted from, while higher levels are believed to be entirely dynamic and a product of their surrounding environments, including bound proteins and associated cations. In 2008, heparin sources were subject to a major contamination with a deadly compound-an over-sulphated chondroitin sulphate polysaccharide-that resulted in excess of 100 deaths within North America alone. In consideration of this, an arsenal of methods to screen for heparin contamination have been applied, based primarily on the detection of over-sulphated chondroitin sulphate. The targeted nature of these screening methods, for this specific contaminant, may leave contamination by other entities poorly protected against, but novel approaches, including library-based chemometric analysis in concert with a variety of spectroscopic methods, could be of great importance in combating future, potential threats.
Collapse
Affiliation(s)
- Anthony Devlin
- Molecular & Structural Biosciences, School of Life Sciences, Keele University, Huxley Building, Keele, Staffordshire ST5 5BG, UK.
| | - Courtney Mycroft-West
- Molecular & Structural Biosciences, School of Life Sciences, Keele University, Huxley Building, Keele, Staffordshire ST5 5BG, UK.
| | - Patricia Procter
- Molecular & Structural Biosciences, School of Life Sciences, Keele University, Huxley Building, Keele, Staffordshire ST5 5BG, UK.
| | - Lynsay Cooper
- Molecular & Structural Biosciences, School of Life Sciences, Keele University, Huxley Building, Keele, Staffordshire ST5 5BG, UK.
| | - Scott Guimond
- Institute for Science and Technology in Medicine, Keele University, Keele, Staffordshire ST5 5BG, UK.
- School of Biological Sciences, University of Liverpool, Crown Street, Liverpool L69 7ZB, UK.
| | - Marcelo Lima
- Molecular & Structural Biosciences, School of Life Sciences, Keele University, Huxley Building, Keele, Staffordshire ST5 5BG, UK.
| | - Edwin Yates
- Molecular & Structural Biosciences, School of Life Sciences, Keele University, Huxley Building, Keele, Staffordshire ST5 5BG, UK.
- School of Biological Sciences, University of Liverpool, Crown Street, Liverpool L69 7ZB, UK.
| | - Mark Skidmore
- Molecular & Structural Biosciences, School of Life Sciences, Keele University, Huxley Building, Keele, Staffordshire ST5 5BG, UK.
- Institute for Science and Technology in Medicine, Keele University, Keele, Staffordshire ST5 5BG, UK.
- School of Biological Sciences, University of Liverpool, Crown Street, Liverpool L69 7ZB, UK.
| |
Collapse
|
6
|
Abstract
Heparin, the widely used anticoagulant drug, is unusual among major pharmaceutical agents being neither single chemical entity nor a defined mixture of compounds. Its composition, while conforming to approximate average disaccharide composition or sulfation levels, exhibits heterogeneity and variability depending on the source, as well as its geographical origin. Furthermore, individual polysaccharide chains, whose physico-chemical properties are extremely similar, cannot be separated with current state-of-the-art techniques, presenting a challenge to those interested in the quality control of heparin, in ensuring its provenance and safety, and those with an interest in investigating the relationships between its structure and biological activity. The review consists of two main sections: The first is the Introduction, comprising (i) The History, Occurrence and Use of Heparin and (ii) Approaches to Structure-Activity Relationships. The second section is Improved Techniques for Structural Analysis, comprising; (i) Separation and Identification, (ii) Spectroscopic Methods, (iii) Enzymatic Approaches and (iv) Other Physico-Chemical Approaches. The ~60 references cover recent technological advances in the study of heparin structural analysis, largely since 2010.
Collapse
Affiliation(s)
- Edwin A Yates
- Department of Biochemistry, Institute of Integrative Biology, University of Liverpool, Crown Street, Liverpool, L69 7ZBUK.
| | - Timothy R Rudd
- Department of Biochemistry, Institute of Integrative Biology, University of Liverpool, Crown Street, Liverpool, L69 7ZBUK; National Institute for Biological Standards and Controls (NIBSC), Blanche Lane, South Mimms, Hertfordshire, EN6 3QG, UK
| |
Collapse
|
7
|
Investigating the relationship between temperature, conformation and calcium binding in heparin model oligosaccharides. Carbohydr Res 2016; 438:58-64. [PMID: 27987423 DOI: 10.1016/j.carres.2016.12.002] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/10/2016] [Revised: 11/30/2016] [Accepted: 12/06/2016] [Indexed: 11/24/2022]
Abstract
Glycosaminoglycans such as heparan sulfate (HS) are major components of the cell surface and extracellular matrix (ECM) of all multicellular animals, connecting cells to each other as well as to their environment. The ECM must, therefore, both sense and accommodate changes to external conditions. Heparin, a model compound for HS, responds to increased temperatures, involving changes in the populations of conformational states with implications for the binding of HS to proteins, cations and, potentially, for its activity. A fully 13C and 15N labelled model octasasccharide; D-GlcNS6S α(1-4) L-IdoA2S [α(1-4) D-GlcNS6S α(1-4) L-IdoA2S]2 α(1-4) D-GlcNS6S α(1-4) L-IdoA1,6an, was studied by 1H, 13C and 15N NMR, revealing complex changes in chemical shifts and conformation, over temperatures (280-305 K), comfortably within the range relevant to terrestrial biology. These complex conformational changes indicated an interaction between the carboxylate group of L-iduronate and D-glucosamine residues that was susceptible to temperature changes in this range, while the well-documented hydrogen bond between the N-sulfamido group of glucosamine and the hydroxyl group at position-3 of iduronate remained intact. Unexpectedly, despite the presence of similar thermally-induced conformational changes in a heparin octasaccharide fraction in the sodium ion form, its subsequent binding to calcium ions and their resulting conformation was stringently maintained, as judged by comparisons of 1H NMR chemical shifts.
Collapse
|
8
|
Pomin VH. ¹H and (15)N NMR Analyses on Heparin, Heparan Sulfates and Related Monosaccharides Concerning the Chemical Exchange Regime of the N-Sulfo-Glucosamine Sulfamate Proton. Pharmaceuticals (Basel) 2016; 9:ph9030058. [PMID: 27618066 PMCID: PMC5039511 DOI: 10.3390/ph9030058] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/07/2016] [Revised: 08/31/2016] [Accepted: 09/03/2016] [Indexed: 12/20/2022] Open
Abstract
Heparin and heparan sulfate are structurally related glycosaminoglycans (GAGs). Both GAGs present, although in different concentrations, N-sulfo-glucosamine (GlcNS) as one of their various composing units. The conditional fast exchange property of the GlcNS sulfamate proton in these GAGs has been pointed as the main barrier to its signal detection via NMR experiments, especially 1H-15N HSQC. Here, a series of NMR spectra is collected on heparin, heparan sulfate and related monosaccharides. The N-acetyl glucosamine-linked uronic acid types of these GAGs were properly assigned in the 1H-15N HSQC spectra. Dynamic nuclear polarization (DNP) was employed in order to facilitate 1D spectral acquisition of the sulfamate 15N signal of free GlcNS. Analyses on the multiplet pattern of scalar couplings of GlcNS 15N has helped to understand the chemical properties of the sulfamate proton in solution. The singlet peak observed for GlcNS happens due to fast chemical exchange of the GlcNS sulfamate proton in solution. Analyses on kinetics of alpha-beta anomeric mutarotation via 1H NMR spectra have been performed in GlcNS as well as other glucose-based monosaccharides. 1D 1H and 2D 1H-15N HSQC spectra recorded at low temperature for free GlcNS dissolved in a proton-rich solution showed signals from all exchangeable protons, including those belonging to the sulfamate group. This work suits well to the current grand celebration of one-century-anniversary of the discovery of heparin.
Collapse
Affiliation(s)
- Vitor H Pomin
- Program of Glycobiology, Institute of Medical Biochemistry Leopoldo de Meis, Federal University of Rio de Janeiro, Rio de Janeiro 21941-590, Brazil.
- University Hospital Clementino Fraga Filho, Federal University of Rio de Janeiro, Rio de Janeiro 21941-913, Brazil.
| |
Collapse
|
9
|
Soares PA, Queiroz IN, Pomin VH. NMR structural biology of sulfated glycans. J Biomol Struct Dyn 2016; 35:1069-1084. [DOI: 10.1080/07391102.2016.1171165] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
Affiliation(s)
- Paulo A.G. Soares
- Program of Glycobiology, Institute of Medical Biochemistry Leopoldo de Meis, and University Hospital Clementino Fraga Filho, Federal University of Rio de Janeiro , Rio de Janeiro, RJ 21941-913, Brazil
| | - Ismael N.L. Queiroz
- Program of Glycobiology, Institute of Medical Biochemistry Leopoldo de Meis, and University Hospital Clementino Fraga Filho, Federal University of Rio de Janeiro , Rio de Janeiro, RJ 21941-913, Brazil
| | - Vitor H. Pomin
- Program of Glycobiology, Institute of Medical Biochemistry Leopoldo de Meis, and University Hospital Clementino Fraga Filho, Federal University of Rio de Janeiro , Rio de Janeiro, RJ 21941-913, Brazil
| |
Collapse
|
10
|
Beecher CN, Larive CK. 1H and 15N NMR Characterization of the Amine Groups of Heparan Sulfate Related Glucosamine Monosaccharides in Aqueous Solution. Anal Chem 2015; 87:6842-8. [DOI: 10.1021/acs.analchem.5b01181] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Consuelo N. Beecher
- Department of Chemistry, University of California − Riverside, Riverside, California 92521, United States
| | - Cynthia K. Larive
- Department of Chemistry, University of California − Riverside, Riverside, California 92521, United States
| |
Collapse
|
11
|
Abstract
Recent NMR studies of the exchangeable protons of GAGs in aqueous solution, including those of the amide, sulfamate, and hydroxyl moieties, have demonstrated potential for the detection of intramolecular hydrogen bonds, providing insights into secondary structure preferences. GAG amide protons are observable by NMR over wide pH and temperature ranges; however, specific solution conditions are required to reduce the exchange rate of the sulfamate and hydroxyl protons and allow their detection by NMR. Building on the vast body of knowledge on detection of hydrogen bonds in peptides and proteins, a variety of methods can be used to identify hydrogen bonds in GAGs including temperature coefficient measurements, evaluation of chemical shift differences between oligo- and monosaccharides, and relative exchange rates measured through line shape analysis and EXSY spectra. Emerging strategies to allow direct detection of hydrogen bonds through heteronuclear couplings offer promise for the future. Molecular dynamic simulations are important in this effort both to predict and confirm hydrogen bond donors and acceptors.
Collapse
Affiliation(s)
- Consuelo N Beecher
- Department of Chemistry, University of California, Riverside, Riverside, CA, 92521, USA,
| | | |
Collapse
|
12
|
Pegeot M, Sadir R, Eriksson I, Kjellen L, Simorre JP, Gans P, Lortat-Jacob H. Profiling sulfation/epimerization pattern of full-length heparan sulfate by NMR following cell culture 13C-glucose metabolic labeling. Glycobiology 2014; 25:151-6. [DOI: 10.1093/glycob/cwu114] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
|
13
|
Mazák K, Beecher CN, Kraszni M, Larive CK. The interaction of enoxaparin and fondaparinux with calcium. Carbohydr Res 2013; 384:13-9. [PMID: 24334236 DOI: 10.1016/j.carres.2013.11.007] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/31/2013] [Revised: 10/24/2013] [Accepted: 11/11/2013] [Indexed: 01/06/2023]
Abstract
The main sites of calcium binding were determined for the low molecular weight heparin drug enoxaparin and the synthetic pentasaccharide Arixtra (fondaparinux). [(1)H,(13)C] HSQC pH titrations were carried out to characterize the acid-base properties of these samples both in the presence and absence of calcium. The differences in the titration curves were used to determine the structural components of enoxaparin and fondaparinux responsible for Ca(2+) binding. In enoxaparin both unsubstituted and 2-O-sulfated iduronic acid residues are important in calcium binding and the presence of the 2-O-sulfo group does not seem to influence the Ca(2+) binding capability of the iduronate ring. In fondaparinux changes in chemical shifts upon Ca(2+) binding were smaller than observed for enoxaparin, and were observed for both the glucuronic acid and 2-O-sulfated iduronic acid residues. In enoxaparin significant perturbations of the chemical shift of the N-sulfoglucosamine anomeric carbon in residues connected to 2-O-sulfated iduronic acid were detected on Ca(2+) binding, however it was not possible to determine whether these changes reflect direct involvement in calcium complexation or result from through space interactions or conformational changes.
Collapse
Affiliation(s)
- Károly Mazák
- Department of Chemistry, University of California, Riverside, Riverside, CA 92521, USA; Department of Pharmaceutical Chemistry, Semmelweis University, Hőgyes E. u. 9, 1092 Budapest, Hungary
| | - Consuelo N Beecher
- Department of Chemistry, University of California, Riverside, Riverside, CA 92521, USA
| | - Márta Kraszni
- Department of Chemistry, University of California, Riverside, Riverside, CA 92521, USA; Department of Pharmaceutical Chemistry, Semmelweis University, Hőgyes E. u. 9, 1092 Budapest, Hungary
| | - Cynthia K Larive
- Department of Chemistry, University of California, Riverside, Riverside, CA 92521, USA.
| |
Collapse
|
14
|
Affiliation(s)
- Vitor H. Pomin
- Program of
Glycobiology, Institute of Medical Biochemistry,
and University Hospital Clementino Fraga Filho, Federal University of Rio de Janeiro, Rio de Janeiro, 21941-913,
Brazil
| |
Collapse
|
15
|
Abstract
Over the past 28 years there have been several thousand publications describing the use of 2D NMR to identify and characterize natural products. During this time period, the amount of sample needed for this purpose has decreased from the 20-50 mg range to under 1 mg. This has been due to both improvements in NMR hardware and methodology. This review will focus on mainly methodology improvements, particularly in pulse sequences, acquisition and processing methods which are particularly relevant to natural product research, with lesser discussion of hardware improvements.
Collapse
|
16
|
Ferreira RB, Tormena CF, Almeida WP. Synthesis and spectroscopic analysis of substituted 2-aminothiazolines. J Mol Struct 2013. [DOI: 10.1016/j.molstruc.2012.12.031] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
|
17
|
Advances in glycosaminoglycanomics by 15N-NMR spectroscopy. Anal Bioanal Chem 2013; 405:3035-48. [DOI: 10.1007/s00216-013-6803-7] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/19/2012] [Revised: 01/25/2013] [Accepted: 01/28/2013] [Indexed: 10/27/2022]
|
18
|
Langeslay DJ, Beecher CN, Naggi A, Guerrini M, Torri G, Larive CK. Characterizing the microstructure of heparin and heparan sulfate using N-sulfoglucosamine 1H and 15N NMR chemical shift analysis. Anal Chem 2013; 85:1247-55. [PMID: 23240897 PMCID: PMC3974173 DOI: 10.1021/ac3032788] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023]
Abstract
Heparin and heparan sulfate (HS) are members of a biologically important group of highly anionic linear polysaccharides called glycosaminoglycans (GAGs). Because of their structural complexity, the molecular-level characterization of heparin and HS continues to be a challenge. The work presented herein describes an emerging approach for the analysis of unfractionated and low molecular weight heparins, as well as porcine and human-derived HS. This approach utilizes the untapped potential of (15)N NMR to characterize these preparations through detection of the NH resonances of N-sulfo-glucosamine residues. The sulfamate group (1)H and (15)N chemical shifts of six GAG microenvironments were assigned based on the critical comparison of selectively modified heparin derivatives, NMR measurements for a library of heparin-derived oligosaccharide standards, and an in-depth NMR analysis of the low molecular weight heparin enoxaparin through systematic investigation of the chemical exchange properties of NH resonances and residue-specific assignments using the [(1)H,(15)N] HSQC-TOCSY experiment. The sulfamate microenvironments characterized in this study include GlcNS(6S)-UA(2S), ΔUA(2S)-GlcNS(6S), GlcNS(3S)(6S)-UA(2S), GlcNS-UA, GlcNS(6S)-red(α), and 1,6-anhydro GlcNS demonstrating the utility of [(1)H,(15)N] HSQC NMR spectra to provide a spectroscopic fingerprint reflecting the composition of intact GAGs and low molecular weight heparin preparations.
Collapse
Affiliation(s)
- Derek J Langeslay
- Department of Chemistry, University of California-Riverside, Riverside, CA, USA
| | | | | | | | | | | |
Collapse
|