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[[File:Bruker Amazon Speed ETD.jpg|thumb|An ion trap mass spectrometer with electron transfer dissociation capability|320x320px]]
'''Electron-transfer dissociation''' ('''ETD''') is a method of [[Fragmentation (mass spectrometry)|fragmenting]]
▲'''Electron-transfer dissociation''' (ETD) is a method of [[Fragmentation (mass spectrometry)|fragmenting]] large gaseous [[Molecular ion|molecular ions]] in a [[mass spectrometer]] between the stages of [[tandem mass spectrometry]] (MS/MS).<ref>{{Cite book|title=Fundamentals of Contemporary Mass Spectrometry|last=Dass|first=Chhabil|publisher=John Wiley & Sons.|year=2007|isbn=978-0-470-11848-1|location=Hoboken, New Jersey|pages=128}}</ref> Similar to [[electron-capture dissociation]], ETD induces fragmentation of large, multiply-charged [[cations]] by transferring [[electron]]s to them.<ref>{{Cite journal|last=Hart-Smith|first=Gene|date=2014-01-15|title=A review of electron-capture and electron-transfer dissociation tandem mass spectrometry in polymer chemistry|url=http://www.sciencedirect.com/science/article/pii/S000326701301235X|journal=Analytica Chimica Acta|series=Polymer Mass Spectrometry|volume=808|pages=44–55|doi=10.1016/j.aca.2013.09.033}}</ref> ETD is used extensively with polymers and biological molecules such as [[Protein|proteins]] and [[Peptide|peptides]] for [[sequence analysis]].<ref>{{Cite journal|last=Brodbelt|first=Jennifer S.|date=2015-12-11|title=Ion Activation Methods for Peptides and Proteins|url=http://pubs.acs.org/doi/abs/10.1021/acs.analchem.5b04563|journal=Analytical Chemistry|language=EN|volume=88|issue=1|pages=30–51|doi=10.1021/acs.analchem.5b04563}}</ref> Transferring an electron causes [[Structure|peptide backbone]] cleavage into [[Peptide sequence tag|c- and z-ions]] while leaving [[Lability|labile]] [[Post-translational modification|post translational modifications]] (PTM) intact.<ref>{{Cite journal|last=Coon|first=Joshua J.,|last2=Syka|first2=John E.P.|last3=Shabanowitz|first3=Jeffrey|last4=Hunt|first4=Donald F.|date=April 2005|title=Tandem Mass Spectrometry for Peptide and Protein Sequence Analysis|url=http://www.biotechniques.com/BiotechniquesJournal/2005/April/Tandem-Mass-Spectrometry-for-Peptide-and-Protein-Sequence-Analysis/biotechniques-45438.html|journal=BioTechniques|doi=|pmid=15884666|access-date=April 15, 2016}}</ref> The method was developed by [[Donald F. Hunt]], [[Joshua Coon]], John E. P. Syka and Jarrod Marto at the [[University of Virginia]].<ref>{{US patent reference | number = 7534622 | y = 2009 | m = 05 | d = 19 | inventor = Donald F. Hunt, Joshua J. Coon, John E.P. Syka, Jarrod A. Marto | title = Electron transfer dissociation for biopolymer sequence mass spectrometric analysis}}</ref>
== History ==
Electron-capture dissociation (ECD) was developed in 1998 to fragment large proteins for mass spectrometric analysis.<ref>{{Cite journal|last=Zubarev|first=Roman A.|last2=Kelleher|first2=Neil L.|last3=McLafferty|first3=Fred W.|date=1998-04-01|title=Electron Capture Dissociation of Multiply Charged Protein Cations. A Nonergodic Process|url=http://dx.doi.org/10.1021/ja973478k|journal=Journal of the American Chemical Society|volume=120|issue=13|pages=3265–3266|doi=10.1021/ja973478k|issn=0002-7863}}</ref> Because ECD requires a large amount of near-thermal electrons (<0.2eV), originally it was used exclusively with [[Fourier transform ion cyclotron resonance|Fourier transform ion cyclotron resonance mass spectrometry]] (FTICR), the most expensive form of MS instrumentation.<ref>{{Cite journal|last=McLafferty|first=Fred W.|last2=Horn|first2=David M.|last3=Breuker|first3=Kathrin|last4=Ge|first4=Ying|last5=Lewis|first5=Mark A.|last6=Cerda|first6=Blas|last7=Zubarev|first7=Roman A.|last8=Carpenter|first8=Barry K.|date=2001-03-01|title=Electron capture dissociation of gaseous multiply charged ions by Fourier-transform ion cyclotron resonance|url=http://link.springer.com/article/10.1016/S1044-0305%2800%2900223-3|journal=Journal of the American Society for Mass Spectrometry|language=en|volume=12|issue=3|pages=245–249|doi=10.1016/S1044-0305(00)00223-3|issn=1044-0305}}</ref> Less costly options such as [[Quadrupole time-of-flight mass spectrometer|quadrupole time-of-flight]] (Q-TOF), [[quadrupole ion trap]] (QIT) and [[linear quadrupole ion trap]] (QLT) instruments used the more energy-intensive [[collision-induced dissociation]] method (CID), resulting in random fragmentation of peptides and proteins.<ref>{{Cite book|url=http://www.sciencedirect.com/science/article/pii/S0076687905020057|title=Collision‐Induced Dissociation (CID) of Peptides and Proteins|last=Mitchell Wells|first=J.|last2=McLuckey|first2=Scott A.|date=2005-01-01|publisher=Academic Press|editor-last=Enzymology|editor-first=BT - Methods in|series=Biological Mass Spectrometry|volume=402|pages=148–185|doi=10.1016/s0076-6879(05)02005-7}}</ref> In 2004 Syka et al announced the creation of ETD, a dissociation method similar to ECD, but using a low-cost, widely available commercial spectrometer. The first ETD experiments were run on a QLT mass spectrometer with an [[electrospray ionization]] (ESI) source.
== Principle of operation ==
Several steps are involved in electron transfer dissociation.
=== Radical anion
In the original ETD experiments [[anthracene]] (C<sub>14</sub>H<sub>10</sub>) was was used to generate reactive radical anions through negative [[chemical ionization]].<ref name="pmid15210983" /> Several [[Aromatic hydrocarbon#Polycyclic aromatic hydrocarbons|polycyclic aromatic hydrocarbon]] molecules have been used in subsequent experiments, with [[fluoranthene]] currently the preferred reagent.<ref>{{Cite journal|last=Chi|first=An|last2=Huttenhower|first2=Curtis|last3=Geer|first3=Lewis Y.|last4=Coon|first4=Joshua J.|last5=Syka|first5=John E. P.|last6=Bai|first6=Dina L.|last7=Shabanowitz|first7=Jeffrey|last8=Burke|first8=Daniel J.|last9=Troyanskaya|first9=Olga G.|date=2007-02-13|title=Analysis of phosphorylation sites on proteins from Saccharomyces cerevisiae by electron transfer dissociation (ETD) mass spectrometry|url=http://www.pnas.org/content/104/7/2193|journal=Proceedings of the National Academy of Sciences|language=en|volume=104|issue=7|pages=2193–2198|doi=10.1073/pnas.0607084104|issn=0027-8424|pmc=1892997|pmid=17287358}}</ref> Fluoranthene has only about 40% efficiency in electron transfer, however, so other molecules with low electron affinity are being sought.<ref name=":0" />
=== Injection and fragmentation ===
[[File:ETD cartoon.tiff|thumb|400px|Multiply-charged precursor ion reacts with radical anion]]
When the precursor cations (proteins or peptides) and radical anions are combined in the ion trap an electron is transferred to the mulitply-charged cation. This forms an unstable positive radical cation with one less positive charge and an odd electron.<ref>{{Cite web|url=https://nationalmaglab.org/user-facilities/icr/techniques/electron-transfer-dissociation|title=Electron Transfer Dissociation|last=|first=|date=August 28, 2015|website=The National High Magnetic Field Laboratory|publisher=|access-date=March 1, 2016}}</ref> Fragmentation takes place along the peptide backbone at a N− Cα bond, resulting in c- and z-type fragment ions.<ref name=":1" />
[[File:ETD Fragmentation.tiff|thumb|400 px|Protein or peptide radical cation fragments into c-ion and z-ion]]
=== Mass analysis ===
Fragmentation caused by ETD allows more complete protein sequence information to be obtained from ETD spectra than from CID tandem mass spectrometry. Because many peptide backbone c- and z- type ions are detected, almost complete sequence coverage of many peptides can be discerned from ETD fragmentation spectra.<ref>{{Cite journal|last=Zhang|first=Qibin|last2=Frolov|first2=Andrej|last3=Tang|first3=Ning|last4=Hoffmann|first4=Ralf|last5=van de Goor|first5=Tom|last6=Metz|first6=Thomas O.|last7=Smith|first7=Richard D.|date=2007-03-15|title=Application of electron transfer dissociation mass spectrometry in analyses of non-enzymatically glycated peptides|url=http://onlinelibrary.wiley.com/doi/10.1002/rcm.2884/abstract|journal=Rapid Communications in Mass Spectrometry|language=en|volume=21|issue=5|pages=661–666|doi=10.1002/rcm.2884|issn=1097-0231|pmc=2731431|pmid=17279487}}</ref> Sequences of 15-40 amino acids at both the N-terminus and the C-terminus of the protein can be read using [[Mass-to-charge ratio|mass-to-charge]] values for the singly and doubly charged ions. These sequences, together with the measured mass of the intact protein, can be compared to database entries for known proteins and to reveal post-translational modifications.<ref>{{Cite journal|last=Chi|first=An|last2=Bai|first2=Dina L.|last3=Geer|first3=Lewis Y.|last4=Shabanowitz|first4=Jeffrey|last5=Hunt|first5=Donald F.|date=2007-01-01|title=Analysis of intact proteins on a chromatographic time scale by electron transfer dissociation tandem mass spectrometry|url=http://www.sciencedirect.com/science/article/pii/S1387380606004477|journal=International Journal of Mass Spectrometry|series=Donald F. Hunt Honour Issue|volume=259|issue=1–3|pages=197–203|doi=10.1016/j.ijms.2006.09.030|pmc=1826913|pmid=17364019}}</ref>
▲:[[File:Peptide fragmentation.gif|alt=|thumb|Peptide Fragmentation |320x320px]]
== Instrumentation ==
:
▲:lkgneworgnelkwgnlewa[[File:Bruker HCT-schematicJune2008.PNG|thumb|440x440px|Bruker high capacity ion trap with ETD (schematic diagram) ]]
== Proteomics ==▼
[[File:LTQ schematic.tiff|thumb|360x360px|Schematic diagram of LTQ with ETD]]
== Changes to the method == ▼
Electron transfer dissociation takes place in an [[ion trap]] mass spectrometer with an electrospray ionization source. The first ETD experiments at the University of Virginia utilized a radio frequency quadrupole linear ion trap (LQT) modified with a chemical ionization (CI) source at the back side of the instrument (see diagram at right).<ref name="pmid15210983" /> Because a spectrum can be obtained in about 300 milliseconds, liquid chromatography is often coupled with the ETD MS/MS.<ref name=":0" /> The disadvantage of using LQT is that the [[mass resolving power]] is less that that of other mass spectrometers.<ref name=":3" />
newer applications including characterization of PTMs, non-tryptic peptides and intact proteins. (Kim Review)▼
Subsequent studies have tried different instrumentation to improve mass resolution. In 2006 a group at Perdue University used a quadrupole/time-of-flight (QqTOF) tandem mass spectrometer with pulsed nano-ESI/atmospheric pressure chemical ionization (APCI) dual ionization source using radical anions of 1,3-dinitrobenzene as the electron donor.<ref>{{Cite journal|last=Xia|first=Yu|last2=Chrisman|first2=Paul A.|last3=Erickson|first3=David E.|last4=Liu|first4=Jian|last5=Liang|first5=Xiaorong|last6=Londry|first6=Frank A.|last7=Yang|first7=Min J.|last8=McLuckey|first8=Scott A.|date=2006-06-01|title=Implementation of Ion/Ion Reactions in a Quadrupole/Time-of-Flight Tandem Mass Spectrometer|url=http://dx.doi.org/10.1021/ac0606296|journal=Analytical Chemistry|volume=78|issue=12|pages=4146–4154|doi=10.1021/ac0606296|issn=0003-2700|pmc=2575740|pmid=16771545}}</ref>
▲== Proteomics ==
ETD is advantageous for the fragmentation of longer peptides or even entire proteins.
For biopharmaceutical characterization, ETD is a powerful fragmentation technique for determining modification sites of labile post-translational modifications (PTMs), which are often difficult to characterize using CID. (also waters page)
▲== Changes to the method ==
▲newer applications including characterization of PTMs, non-tryptic peptides and intact proteins. (Kim Review)
lectron-transfer and higher-energy collision dissociation (EThcD) is a combination ETD and HCD where the peptide precursor is initially subjected to an ion/ion reaction with [[fluoranthene]] anions in a [[linear ion trap]], which generates c- and z-ions.<ref>{{cite journal|last=Frese|first=Christian K.|author2=A. F. Maarten Altelaar |author3=Henk van den Toorn |author4=Dirk Nolting |author5=Jens Griep-Raming |author6=Albert J. R. Heck |author7=Shabaz Mohammed |title=Toward full peptide sequence coverage by dual fragmentation combining electron-transfer and higher-energy collision dissociation tandem mass spectrometry|journal=Anal. Chem.|date=November 20, 2012|pmid=23106539 |doi=10.1021/ac3025366 |volume=84 |issue=22 |pages=9668–73}}</ref> In the second step HCD all-ion fragmentation is applied to all ETD derived ions to generate b- and y- ions prior to final analysis in the orbitrap analyzer.<ref>{{cite journal|last=Olsen JV|author2=Macek B |author3=Lange O |author4=Makarov A |author5=Horning S |author6=Mann M |title=Higher-energy C-trap dissociation for peptide modification analysis.|journal=Nature Methods|date=September 2007|volume=4|issue=9|pages=709–712|url=http://www.ncbi.nlm.nih.gov/pubmed/17721543/ |doi=10.1038/nmeth1060 |pmid=17721543}}</ref> This method employs dual fragmentation to generate ion- and thus data-rich MS/MS spectra for peptide sequencing and [[Post-translational modification|PTM]] localization.<ref>{{cite journal|last=Frese|first=Christian K.|author2=Houjiang Zhou |author3=Thomas Taus |author4=A. F. Maarten Altelaar |author5=Karl Mechtler |author6=Albert J. R. Heck |author7=Shabaz Mohammed |title=Unambiguous Phosphosite Localization using Electron-Transfer/Higher-Energy Collision Dissociation (EThcD)|journal=J Proteome Res.|date=March 1, 2013|pmc=3588588 |pmid=23347405 |doi=10.1021/pr301130k |volume=12 |issue=3 |pages=1520–5}}</ref>
== See also ==
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