CN102043011B - Method for preprocessing and identifying electron transfer dissociation (ETD) mass spectrum - Google Patents
Method for preprocessing and identifying electron transfer dissociation (ETD) mass spectrum Download PDFInfo
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Abstract
The invention provides a method for preprocessing an electron transfer dissociation (ETD) mass spectrum, comprising the steps of: calculating a mass to charge ratio and a charge state of a parent ion; calculating the possible areas of a parent ion peak and isotopic peaks thereof in the ETD mass spectrum; calculating the possible areas of a series of derivative peaks of the parent ion in the ETD mass spectrum; calculating the possible areas of neutral lost peaks of the parent ion in the ETD mass spectrum; and removing the spectrum peaks in the calculated areas in the ETD mass spectrum so as to remove the non-fragmented parent ion peaks, the series of derivative peaks of the parent ion and the neutral lost peaks of the parent ion.
Description
Technical field
The present invention relates to the identification of proteins field, particularly mass spectral preprocess method of electron transport cracking and authentication method.
Background technology
In molecular biology, " central dogma " followed in the propagation of information, and promptly DNA generates mRNA through transcription, and mRNA generates protein through translation process.Generating the process of protein from RNA translation, 20 seed amino acids are called as peptide with the peptide bond order formed chain molecule that links to each other, and wherein molecular weight reaches certain other peptide of level and then is called as protein.The kind of protein is varied, and the process that identifies the particular type of a certain protein is called as identification of protein.The method of identification of protein mainly is with being compared through the resulting theoretical tandem mass spectrum of Theoretical Calculation by experiment tandem mass spectrum that protein example generated to be identified and protein sequence, obtaining protein to be identified according to comparative result in the prior art.Can find out from the process of identification of protein, utilize tandem mass spectrum on a large scale identification of protein be a underlying issue in current proteomics field.The quality of tandem mass spectrum data has directly determined the reliability of identification of proteins.
When generating the experiment tandem mass spectrum, the protease hydrolytic that the protein example of being made up of polypeptide at first is chosen forms peptide mixer; Then peptide mixer is separated; The peptide of different physicochemical property successively is ionized; Peptide ion cracked formation fragmention under energy with extra fine quality charge ratio; Fragmention is separated to form peptide fragment ionic spectrum with detecting, and it is the experiment tandem mass spectrum that this fragmention is composed.
The fragmentate method of ion of peptide ion fragmentation is called as the polypeptide fragmentation method; Polypeptide fragmentation method the most commonly used in the prior art is collision-induced cracking (Collision-induced dissociation; CID), this method is mainly used in the peptide section that trypsase (Trypsin) enzyme is cut.When adopting the cracked peptide ion of this method, it is master's fragment that fragmentation produces with b and y type usually.Corresponding proteins matter authentication method also mainly is to utilize this quasi-molecular ions of two types to participate in actual coupling, generally depends on coupling with the reliable matching result of database sequence and goes up the more higher continuous spectrum peak of intensity.CID has brought into play vital role in large-scale identification of proteins, the instance of a lot of successful Application has been arranged.
Along with going deep into gradually of proteomics research; It is found that and only utilize CID can not solve all problems, particularly for long, with a plurality of electric charges, or the stronger polypeptide of alkalescence; Mass spectrum through the CID fragmentation method produces is second-rate, and available effective information is less relatively.In addition; The polypeptide of posttranslational modification has taken place for common phosphorylation and glycosylation etc.; In the CID fragmentation, the neutral loss of parent ion (like phosphate group or polysaccharide group) often accounts for leading approach, and this also causes the fragmention information relevant with sequence to be weakened.Therefore, seek the important development direction that new more effective polypeptide fragmentation method has become the identification of proteins field recent years.
1998, (Electron capture dissociation, discovery ECD) impelled the polypeptide fragmentation method based on electronics in identification of proteins, to obtain gradually to use in the electron capture cracking.Different fully with CID based on the basic mechanism of collision energy reallocation; ECD makes protein or polypeptide ion moment chipping through low-energy free electron and protonated protein or the heat release of polypeptide ionic interaction; It is a non-ergodic process, and it is master's fragment that cracking mainly produces with c and z type.Because in ion trap mass spectrometer, will hold the difficulty that kation and free electron face technically simultaneously, ECD is mainly used on the Fourier Transform Ion cyclotron Resonance mass spectrometer.Because this instrument costs an arm and a leg, operation expense is high, the application of ECD in proteomics only is confined to minority and has in this high-end mass spectrometric laboratory, do not obtain to promote the use of widely.
To the limitation of ECD on instrument and the inspiration that receives the ECD technology, 2004 with the cracked technology of the similar another kind of electronics of ECD---(Electron transferdissociation ETD) arises at the historic moment in the electron transport cracking.It is to interact through the negative ion that carries electronics and polypeptide or protein kation to make protein or polypeptide ion produce cracked.Different with ECD is that it can be realized on the ion trap mass spectrometer of widespread usage, so just impels the polypeptide fragmentation method based on electronics in the peptide sequence analysis, to obtain widespread use.
Though ETD finds to have only the time in 6 years so far; But because it is exclusive in long sequence and posttranslational modification advantage analytically; Main mass spectrometer company has all released the equipment that has the ETD function at present, and applying of these equipment produced large-scale ETD mass spectrometric data.Yet what be not complementary with equipment research and development speed is that the analytical approach development of ETD mass spectrometric data is still slow, does not obtain enough attention.Compare with the CID mass spectrum, the ETD mass spectrum shows a lot of different features, like significant parent ion peak and derive peak and neutral loss peak etc.Caused the present poor efficiency of most authentication method on the ETD MASS SPECTRAL DATA ANALYSIS like this, developing and develop a kind of effective ETD mass spectrometric data authentication method becomes important demand.
Summary of the invention
The objective of the invention is to overcome that existing method is low to ETD MASS SPECTRAL DATA ANALYSIS efficient, the defective of poor accuracy, thus provide a kind of efficiently, ETD MASS SPECTRAL DATA ANALYSIS, authentication method accurately.
To achieve these goals, the invention provides a kind of electron transport cracking mass spectrum preprocess method, comprising:
The mass-to-charge ratio and the state of charge of step 1), calculating parent ion;
Step 2), according to the mass-to-charge ratio and the state of charge of parent ion, calculate the zone that parent ion peak and isotopic peak thereof possibly occur in electron transport cracking mass spectrum;
Step 3), according to the mass-to-charge ratio and the state of charge of parent ion, calculate the zone that the series derivatives peak of parent ion possibly occur in electron transport cracking mass spectrum;
Step 4), according to the mass-to-charge ratio and the state of charge of parent ion, calculate the zone that the neutral loss peak of parent ion possibly occur in electron transport cracking mass spectrum;
Step 5), with in the said electron transport cracking mass spectrum by step 2), spectrum peak in the zone that calculates of step 3) and step 4) removes, to remove not cracked parent ion peak, the series derivatives peak of parent ion and the neutral loss peak of parent ion;
Wherein, described step 2), the sequencing between step 3) and the step 4) can change.
In the technique scheme, described step 2) comprising:
Step 2-1), according to said parent ion mass-to-charge ratio and state of charge, calculate said parent ion quality;
Step 2-2), combine said parent ion quality and the mass spectral measuring accuracy of electron transport cracking; Calculate parent ion peak and its isotopic peak and the corresponding indeterminacy error range of said measuring accuracy, obtain the zone that said parent ion peak and isotopic peak thereof possibly occur in electron transport cracking mass spectrum.
In the technique scheme, described step 3) comprises:
Step 3-1), according to said parent ion mass-to-charge ratio and state of charge, calculate said parent ion quality;
Step 3-2), by the state of charge at said parent ion quality and the said peak of deriving, calculate the mass-to-charge ratio at the said peak of deriving;
Step 3-3), the mass-to-charge ratio and the mass spectral measuring accuracy of said electron transport cracking that combine the said peak of deriving; Calculate said peak and the corresponding indeterminacy error range of said measuring accuracy of deriving, obtain the zone that the series derivatives peak of said parent ion possibly occur in electron transport cracking mass spectrum.
In the technique scheme, described step 4) comprises:
Step 4-1), according to said parent ion mass-to-charge ratio and state of charge, calculate said parent ion quality;
Step 4-2), said parent ion quality is deducted the quality of neutral loss, obtain the quality at neutral loss peak;
Step 4-3), obtain the mass-to-charge ratio at neutral loss peak by the state of charge at the quality at said neutral loss peak and said neutral loss peak;
Step 4-4), the mass-to-charge ratio and the mass spectral measuring accuracy of said electron transport cracking that combine said neutral loss peak; Calculate the corresponding indeterminacy error range of said neutral loss peak and said measuring accuracy, obtain the zone that the neutral loss peak of said parent ion possibly occur in electron transport cracking mass spectrum.
The present invention also provides a kind of identification of proteins method, comprising:
Step 1), employing ETD method are carried out enzymolysis, cracked to protein example to be identified, obtain the ETD experiment tandem mass spectrum of this protein example, adopt described electron transport cracking mass spectrum preprocess method that this ETD experiment tandem mass spectrum is carried out pre-service;
Step 2), according to the state of charge of parent ion, when being chosen in the search theory tandem mass spectrum the ionic type that will mate;
Step 3), search theory tandem mass spectrum compare said theoretical tandem mass spectrum and the resulting ETD experiment tandem mass spectrum through filtration of step 1), realize the evaluation to protein according to comparative result.
In the technique scheme, described step 2) comprising:
Step 2-1) if parent ion has two electric charges, the ionic type of then selecting to mate comprises c, z, c-1 and z+1;
Step 2-2) if the charge number of parent ion greater than two, the ionic type of then selecting to mate comprises c, z and z+1.
The invention has the advantages that:
1, the present invention has considered the mass spectral characteristics of ETD, has avoided serial cutting edge of a knife or a sword the interference in actual fragment ion peak matching process relevant with parent ion through adopting pretreated method.
2, the present invention adopts the ETD mass spectrum authentication method of different fragmention types respectively according to the parent ion state of charge, has reached the purpose that improves identification result.
Description of drawings
Fig. 1 is the ETD spectrogram of polypeptide A VYAGENFHHGDKL;
Fig. 2 is the process flow diagram of electron transport cracking mass spectrum preprocess method of the present invention;
Fig. 3 is for carrying out the histogram that ionic type and mass deviation thereof are added up to a collection of from the mass spectrometric a large amount of ETD of LTQ-Orbitrap and CID mass spectrum; Wherein,
Fig. 3 (a) and Fig. 3 (b) are the polypeptide ETD mass spectrum of two electric charges of parent ion band (+2);
Fig. 3 (c) and Fig. 3 (d) are the peptide C ID mass spectrum of two electric charges of parent ion band (+2);
Fig. 3 (e) and Fig. 3 (f) are the polypeptide ETD mass spectrum of three electric charges of parent ion band (+3);
Fig. 4 is the comparison diagram of the qualification result of the qualification result of the pFind software that adopts the inventive method and Mascot software; Wherein,
Fig. 4 (a) for identify+the ETD spectrogram quantity of 2 peptides;
Fig. 4 (b) for identify+the ETD spectrogram quantity of 3 peptides;
Fig. 4 (c) for identify+the ETD spectrogram quantity of 4 peptides;
Fig. 4 (d) for identify+the ETD spectrogram quantity of 5 peptides;
Fig. 5 is the comparison diagram of pFind software ionic type qualification result when adopting the inventive method to do pre-service and do not do pre-service.
Embodiment
Below in conjunction with accompanying drawing and embodiment the present invention is explained.
Before the present invention is elaborated,, the implication of several technical terms involved among the present invention is explained respectively for the ease of understanding.
Parent ion: be meant from the one-level spectrum and select cracked peptide ion.
The peak of deriving: be meant protonated polypeptide ion and electron interaction, quality is constant basically and spectrum peak that electric charge reduces.
Neutral loss peak: be meant the side chain generation neutral loss at the peak of deriving and the spectrum peak that produces.
After some involved technical terms are done and explained in to the present invention,, the ETD experiment tandem mass spectrum that is produced by the ETD method is analyzed below in conjunction with instance.
Provided the ETD spectrogram of a polypeptide A VYAGENFHHGDKL among Fig. 1, this spectrogram produces from LTQ-Orbitrap XL mass spectrometer, and its pairing parent ion has three electric charges.This is the spectrogram that can represent ETD cracking characteristic feature that reliable qualification result is arranged.In this spectrogram, include the fragment ion peak outer (peak that is marked as the beginning letter with c or z among the figure) of the c that marks out according to peptide sequence and z type, also include a plurality of not spectrum peaks of mark.The spectrum peak of low-intensity (promptly highly lower spectrum peak) is mostly from the noise of electronic signal in these spectrum peaks; Relatively those higher spectrum peaks of fragment ion peak strength ratio then are the series of peaks relevant with parent ion, like the peak of deriving (Charge-reduced Peaks) of not cracked parent ion peak, parent ion, neutral loss peak etc.Specifically, in Fig. 1, be labeled as [M] +++the spectrum peak be the top in this spectrogram, it has represented not cracked parent ion peak, its relative intensity is 100%.Be labeled as [M] among Fig. 1 ++ with [M]+two spectrum peaks be to produce through anionic repeatedly chemical reaction with charged son by protonated polypeptide parent ion; Most parent ion in the polypeptide parent ion of these spectrum peak representatives does not have chipping; But owing to obtained electronics; Make the corresponding minimizing of its state of charge, electronics of every acquisition, charge number just subtracts 1.Be labeled as [M] among Fig. 1 ++ with [M]+the left field at spectrum peak in not those higher relatively spectrum peaks of intensity of mark correspond respectively to neutral loss peak from its ion of deriving, the neutral loss peak of parent ion is then not obvious in the ETD mass spectrum.From finding out to above-mentioned not cracked parent ion peak, the peak of deriving of parent ion, the description at neutral loss peak; The intensity at these spectrum peaks is all higher relatively; If therefore these spectrum peaks and fragmentation of ions peak are all mated with the theoretical tandem mass spectrum that obtains according to sequence prediction simultaneously; Will inevitably cause the mistake coupling so, and the mistake coupling greatly has influence on the reliability of qualification result possibly.Just for the above reasons; Need be to filtering by the ETD that protein generated experiment tandem mass spectrum to be identified; The high-intensity relatively spectrum peak that those and fragmention relation is very not big identifies; And from the experiment tandem mass spectrum, remove, influence to avoid or to significantly reduce the mistake coupling that causes owing to existing of these spectrum peaks.
With reference to figure 2, in the face of carrying out pretreated method, explains ETD experiment tandem mass spectrum down.
Step 1), at first, calculate parent ion mass-to-charge ratio MZ and state of charge N (be parent ion with charge number).The mass-to-charge ratio and the state of charge that calculate parent ion need rely on the mass spectral parent ion relevant information of polypeptide one-level, and the mass spectral parent ion information of polypeptide one-level can obtain through mass spectrometer.For high-resolution mass spectrometer,, generally can accurately obtain its state of charge through measuring the parent ion isotopic peak pattern that obtains like FTICR and Orbitrap.And for the ion trap mass spectrometer of low resolution, the state of charge of polypeptide parent ion in most cases is not sure of, can solve through two kinds of approach so usually, and the one, suppose several kinds of possible state of charge, search for evaluation respectively by these electric charges.Judge through the confidence level that compares qualification result which kind of state of charge this parent ion possibly be with at last; The 2nd, predict possible state of charge through computer software, as several kinds of Software tools have been arranged at present, such as Charger and CPM.
Step 2), then, calculate the possible appearance zone of parent ion peak and isotope thereof.Mass-to-charge ratio MZ and state of charge N according to parent ion can calculate parent ion mass M Z * N, in conjunction with spectrogram, are easy to identify the possible appearance zone of parent ion peak, comprise its isotopic peak and with the corresponding indeterminacy error range of measuring accuracy.
Step 3), follow again, calculate the zone that the series derivatives peak of parent ion possibly occur.The implication at the peak of deriving of parent ion is explained in preamble, if the charge number of parent ion is N, so the state of charge at its series derivatives peak be respectively N-1, N-2 ..., 1.That is to say, will have N-1 the peak of deriving to be present in (if their mass-to-charge ratio is all in measurement range of mass spectrometer) in the ETD mass spectrum in theory, and their relative intensity is compared higher or suitable with fragmention.Mass-to-charge ratio MZ and state of charge N according to parent ion; The quality that can calculate parent ion is MZ * N; If the state of charge at pairing certain peak of deriving of this parent ion is K (K is a certain integer); The mass-to-charge ratio that just can calculate this peak of deriving is MZ * N/K, K=N-1, N-2 ..., 1.After the mass-to-charge ratio at peak that obtains deriving, just can estimate the zone that these peaks of deriving possibly occur through calculating according to mass spectral measuring accuracy.
Step 4), is then calculated the zone that the neutral loss peak possibly occur.Through discovering, in the polypeptide fragmentation, the neutral loss that is taken place mainly comprises loses ammonia, dehydration, mistake CO etc.Suppose to represent with a the quality of neutral loss, the mass-to-charge ratio of parent ion is MZ, and the charge number of parent ion is N, the neutral loss peak mass-to-charge ratio of the ion of then deriving for (MZ * N-a)/K, K=N-1, N-2 ..., 1.After the mass-to-charge ratio that obtains the neutral loss peak, just can estimate the zone that the neutral loss peak possibly occur according to mass spectral measuring accuracy.
Step 5), last; After the zone that possibly belong at the neutral loss peak of series derivatives peak that calculates not cracked parent ion peak, parent ion and parent ion; Just can remove the spectrum peak in these zones; Thereby reach the purpose at neutral loss peak of series derivatives peak and the parent ion of the not cracked parent ion peak of removal, parent ion, the influence of avoiding these spectrum peaks to cause to the qualification result reliability with the mistake coupling of theoretical fragmention.
More than be that ETD experiment tandem mass spectrum is carried out the explanation of pretreated method; It is to be noted; Step 2 in this method), sequencing not in fact between step 3) and the step 4), so their order can change, and is not limited to above-mentioned explanation.
After obtaining the pretreated experiment tandem mass spectrum of process, can this experiment tandem mass spectrum and theoretical tandem mass spectrum be compared, to realize the evaluation of protein.But in process relatively, whether suitable the ionic type that need when theory of computation tandem mass spectrum, select institute to mate, ionic type are selected to such an extent that directly determined to mate the mark that obtains just.For the CID mass spectrum, usually multiselect is with the ion of b and y type, and for the ETD mass spectrum, and multiselect is with the ion of c and z type, but we discover that this also is nowhere near, the situation of reality is much complicated.Discover; For the ETD mass spectrum; The state of charge of parent ion has vital decisive action to its cracked behavior (or cracking rule), and particularly for the parent ion of two electric charges and parent ion with a plurality of electric charges (more than two electric charges), its ETD mass spectral characteristic has bigger difference.For example, Fig. 3 carries out the histogram of ionic type and mass deviation statistics thereof to a collection of from the mass spectrometric a large amount of ETD of LTQ-Orbitrap and CID mass spectrum, and horizontal ordinate is wherein represented the mass deviation of actual ions and theoretical ion, and unit is Da; The quantity of the ion of the corresponding mass deviation that ordinate is represented to occur.From figure, can find out; Polypeptide ETD mass spectrum for two electric charges of parent ion band (+2); With z, z+1 (Fig. 3 (a)), c-1 and four kinds of ions of c (Fig. 3 (b)) is main; Corresponding CID spectrum is main with the ion of b (Fig. 3 (c)) and y (Fig. 3 (d)) type then, does not find that the ion of resetting takes place similar ETD mass spectrum, like z+1 and c-1.Therefore; Mass spectral evaluation need consider to be different from the characteristics of CID spectrum for ETD; Participate in coupling if only consider the ion of two types of z and c, will ignore to fall a large amount of rearrangement ions, thereby significantly reduce the available effective information that is being contained in the ETD mass spectrum.Polypeptide ETD mass spectrum for two electric charges of polypeptide ETD mass spectrum and parent ion band of two above electric charges of parent ion band has significantly different again.Fig. 3 (e) and Fig. 3 (f) show the polypeptide ETD mass spectrum with the parent ion of three electric charges; We find with the ETD spectrogram of two electric charges different be not observe tangible c-1 ion appearance; In addition; Compare with the quantity of z ion, the relative scale of z+1 ion also reduces to some extent, and this is the mass spectral characteristic feature of multi-charge ETD.
For the above reasons, when the ionic type of selecting from theoretical tandem mass spectrum to be mated, need carry out relevant operation respectively according to the state of charge of parent ion.Concrete operations are following:
If 1 polypeptide parent ion has two electric charges, then when search database and theoretical tandem mass spectrum mated, the ionic type that selection will be mated was four kinds: c, z, c-1 and z+1 (only considering the fragmention of single electric charge);
If the charge number of 2 polypeptide parent ions is greater than two, then when search database and theoretical tandem mass spectrum mated, the ionic type that selection will be mated was three kinds: c, z and z+1 (comprising from the fragmention of 1 to N-1 electric charge).
Above-mentioned disposal route is through showing on the lot of data verification experimental verification: select ionic type can improve the quality and quantity of ETD mass spectrum qualification result greatly according to the parent ion charge number, proved and should handle the validity on the ionic type method.
Selected according to the parent ion state of charge after the ionic type that will mate; The ETD mass spectrum is set again identifies needed other parameters of search; Quality allowable error, posttranslational modification, enzyme like parent ion and fragmention are cut information etc.; Just can utilize these information searches ETD experiment tandem mass spectrum data then, this search procedure can realize through correlation search engine of the prior art, like pFind.After obtaining Search Results, can adopt method, filter out reliable qualification result, produce the qualification result report according to the false positive rate that requires in advance such as positive and negative sequence library (Target-DecoyStrategy).
Fig. 4 is for after being applied to pFind software with said method; With the qualification result of this software and the synoptic diagram that is compared by the qualification result of universally recognized Mascot software in the industry; Wherein, Fig. 4 (a) for identify+the ETD spectrogram quantity of 2 peptides, Fig. 4 (b) for identify+the ETD spectrogram quantity of 3 peptides; Fig. 4 (c) for identify+the ETD spectrogram quantity of 4 peptides, Fig. 4 (d) for identify+the ETD spectrogram quantity of 5 peptides.From each figure, can find out that pFind has comprised the result of Mascot basically, prove that method of the present invention has very high accuracy.
Provided the comparison diagram of pFind software ionic type qualification result when adopting the inventive method to do pre-service and do not do pre-service among Fig. 5, after the process pre-service, the spectrogram number that can identify has obvious increase.
It should be noted last that above embodiment is only unrestricted in order to technical scheme of the present invention to be described.Although the present invention is specified with reference to embodiment; Those of ordinary skill in the art is to be understood that; Technical scheme of the present invention is made amendment or is equal to replacement, do not break away from the spirit and the scope of technical scheme of the present invention, it all should be encompassed in the middle of the claim scope of the present invention.
Claims (7)
1. electron transport cracking mass spectrum preprocess method comprises:
The mass-to-charge ratio and the state of charge of step 1), calculating parent ion;
Step 2), according to the mass-to-charge ratio and the state of charge of parent ion, calculate the zone that parent ion peak and isotopic peak thereof possibly occur in electron transport cracking mass spectrum;
Step 3), according to the mass-to-charge ratio and the state of charge of parent ion, calculate the zone that the series derivatives peak of parent ion possibly occur in electron transport cracking mass spectrum;
Step 4), according to the mass-to-charge ratio and the state of charge of parent ion, calculate the zone that the neutral loss peak of parent ion possibly occur in electron transport cracking mass spectrum;
Step 5), with in the said electron transport cracking mass spectrum by step 2), spectrum peak in the zone that calculates of step 3) and step 4) removes, to remove not cracked parent ion peak, the series derivatives peak of parent ion and the neutral loss peak of parent ion;
Wherein, described step 2), the execution of step 3) and step 4) does not have sequencing.
2. electron transport cracking mass spectrum preprocess method according to claim 1 is characterized in that described step 2) comprising:
Step 2-1), according to said parent ion mass-to-charge ratio and state of charge, calculate said parent ion quality;
Step 2-2), combine said parent ion quality and the mass spectral measuring accuracy of electron transport cracking; Calculate parent ion peak and its isotopic peak and obtain corresponding indeterminacy error range, obtain the zone that said parent ion peak and isotopic peak thereof possibly occur in electron transport cracking mass spectrum according to said measuring accuracy.
3. electron transport cracking mass spectrum preprocess method according to claim 1 is characterized in that described step 3) comprises:
Step 3-1), according to said parent ion mass-to-charge ratio and state of charge, calculate said parent ion quality;
Step 3-2), by the state of charge at said parent ion quality and the said peak of deriving, calculate the mass-to-charge ratio at the said peak of deriving;
Step 3-3), the mass-to-charge ratio and the mass spectral measuring accuracy of said electron transport cracking that combine the said peak of deriving; Calculate said peak and the corresponding indeterminacy error range of said measuring accuracy of deriving, obtain the zone that the series derivatives peak of said parent ion possibly occur in electron transport cracking mass spectrum.
4. electron transport cracking mass spectrum preprocess method according to claim 1 is characterized in that described step 4) comprises:
Step 4-1), according to said parent ion mass-to-charge ratio and state of charge, calculate said parent ion quality;
Step 4-2), said parent ion quality is deducted the quality of neutral loss, obtain the quality at neutral loss peak;
Step 4-3), obtain the mass-to-charge ratio at neutral loss peak by the state of charge at the quality at said neutral loss peak and said neutral loss peak;
Step 4-4), the mass-to-charge ratio and the mass spectral measuring accuracy of said electron transport cracking that combine said neutral loss peak; Calculate the corresponding indeterminacy error range of said neutral loss peak and said measuring accuracy, obtain the zone that the neutral loss peak of said parent ion possibly occur in electron transport cracking mass spectrum.
5. identification of proteins method comprises:
Step 1), employing ETD method are carried out enzymolysis, cracked to protein example to be identified; Obtain the ETD experiment tandem mass spectrum of this protein example, adopt the electron transport cracking mass spectrum preprocess method of one of claim 1-4 that this ETD experiment tandem mass spectrum is carried out pre-service;
Step 2), according to the state of charge of parent ion, when being chosen in the search theory tandem mass spectrum the ionic type that will mate;
Step 3), search theory tandem mass spectrum compare said theoretical tandem mass spectrum and the pretreated ETD experiment of the resulting process of step 1) tandem mass spectrum, realize the evaluation to protein according to comparative result.
6. identification of proteins method according to claim 5 is characterized in that, described step 2) comprise that when parent ion has two electric charges the ionic type that selection will be mated comprises c type ion, z type ion, c-1 type ion and z+1 type ion.
7. identification of proteins method according to claim 5 is characterized in that, described step 2) when comprising that also charge number when parent ion is greater than two, the ionic type that selection will be mated comprises c type ion, z type ion and z+1 type ion.
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Non-Patent Citations (3)
| Title |
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| Paulo C.Carvalho et al.Charge Prediction Machine:Tool for Inferring Precursor Charge States of Electron Transfer Dissociation Tandem Mass Spectra.《Analytical Chemistry》.2009, * |
| Rovshan G.Sadygov et al.Charger:Combination of Signal Processing and Statistical Learning Algorithms for Precursor Charge-State Determination from Electron-Transfer Dissociation Spectra.《Analytical Chemistry》.2008, * |
| 孙瑞祥等.基于质谱技术的计算蛋白质组学研究.《中国科学 E辑 信息科学》.2006, * |
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