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OpenMS
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Extracts and normalizes isobaric labeling information from an LC-MS/MS experiment.
| pot. predecessor tools | → IsobaricAnalyzer → | pot. successor tools |
|---|---|---|
| PeakPickerHiRes | IDMapper | |
| FileFilter |
The input MSn spectra have to be in centroid mode for the tool to work properly. Use e.g. PeakPickerHiRes to perform centroiding of profile data, if necessary.
This tool currently supports iTRAQ 4-plex and 8-plex, and TMT 6-plex, 10-plex, 11-plex, 16-plex, and 18-plex and higher labeling methods. It extracts the isobaric reporter ion intensities from centroided MS2 or MS3 data (MSn), then performs isotope correction and stores the resulting quantitation in a consensus map, in which each consensus feature represents one relevant MSn scan (e.g. HCD; see parameters select_activation and min_precursor_intensity). The MS level for quantification is chosen automatically, i.e. if MS3 is present, MS2 will be ignored. For intensity, the closest non-zero m/z signal to the theoretical position is taken as reporter ion abundance. The position (RT, m/z) of the consensus centroid is the precursor position in MS1 (from the MS2 spectrum); the consensus sub-elements correspond to the theoretical channel m/z (with m/z values of 113-121 Th for iTRAQ and 126-131 Th for TMT, respectively).
For all labeling techniques, the search radius (reporter_mass_shift) should be set as small as possible, to avoid picking up false-positive ions as reporters. Usually, Orbitraps deliver precision of about 0.0001 Th at this low mass range. Low intensity reporters might have a slightly higher deviation. By default, the mass range is set to ~0.002 Th, which should be sufficient for all instruments (~15 ppm). The tool will throw an Exception if you set it below 0.0001 Th (~0.7ppm). The tool will also throw an Exception if you set reporter_mass_shift > 0.003 Th for TMT-10plex and TMT-11plex, since this could lead to ambiguities with neighbouring channels (which are ~0.006 Th apart in most cases).
For quality control purposes, the tool reports the median distance between the theoretical vs. observed reporter ion peaks in each channel. The search radius is fixed to 0.5 Th (regardless of the user defined search radius). This allows to track calibration issues. For TMT-10plex, these results are automatically omitted if they could be confused with a neighbouring channel, i.e. exceed the tolerance to a neighbouring channel with the same nominal mass (C/N channels). If the distance is too large, you might have a m/z calibration problem (see InternalCalibration).
Isotope correction is done using non-negative least squares (NNLS), i.e.:
Minimize ||Ax - b||, subject to x >= 0, where b is the vector of observed reporter intensities (with "contaminating" isotope species), A is a correction matrix (as supplied by the manufacturer of the labeling kit) and x is the desired vector of corrected (real) reporter intensities. Other software tools solve this problem by using an inverse matrix multiplication, but this can yield entries in x which are negative. In a real sample, this solution cannot possibly be true, so usually negative values (= negative reporter intensities) are set to zero. However, a negative result usually means that noise was not properly accounted for in the calculation. We thus use NNLS to get a non-negative solution, without the need to truncate negative values. In the (usual) case that inverse matrix multiplication yields only positive values, our NNLS will give the exact same optimal solution.
The correction matrices can be found (and changed) in the INI file (parameter correction_matrix of the corresponding labeling method). However, these matrices for both 4-plex and 8-plex iTRAQ are now stable, and every kit delivered should have the same isotope correction values. Thus, there should be no need to change them, but feel free to compare the values in the INI file with your kit's certificate. For TMT (6-plex and 10-plex) the values have to be adapted for each kit: Modify the correction matrix according to the data in the product data sheet of your charge:
Data sheet: Mass Tag Repoter Ion -2 -1 Monoisotopic +1 +2 126 126.12776 0.0% 0.0% 100% 5.0% 0.0% 127N 127.124761 0.0% 0.2% 100% 4.6% 0.0% ...
Corresponding correction matrix:
[0.0/0.0/5.0/0.0, 0.0/0.2/4.6/0.0, ...
The command line parameters of this tool are:
IsobaricWorkflow -- Calculates isobaric quantitative values for peptides
Full documentation: http://www.openms.de/doxygen/nightly/html/TOPP_IsobaricWorkflow.html
Version: 3.5.0-pre-nightly-2025-11-12 Nov 13 2025, 02:53:18, Revision: 9b55e34
To cite OpenMS:
+ Pfeuffer, J., Bielow, C., Wein, S. et al.. OpenMS 3 enables reproducible analysis of large-scale mass spec
trometry data. Nat Methods (2024). doi:10.1038/s41592-024-02197-7.
Usage:
IsobaricWorkflow <options>
This tool has algorithm parameters that are not shown here! Please check the ini file for a detailed descript
ion or use the --helphelp option
Options (mandatory options marked with '*'):
-type <mode> Isobaric Quantitation method used
in the experiment. (default: 'itraq
4plex') (valid: 'itraq4plex', 'itra
q8plex', 'tmt10plex', 'tmt11plex',
'tmt16plex', 'tmt18plex', 'tmt6plex
')
-in <file>* Input centroided spectrum files
(valid formats: 'mzML')
-in_id <file>* Corresponding input PSMs (valid
formats: 'idXML')
-exp_design <file> Experimental design file (optional)
. If not given, the design is assum
ed to be unfractionated. (valid
formats: 'tsv')
-out <file>* Output consensusXML file (valid
formats: 'consensusXML')
-out_mzTab <file>* Output mzTab file with quantitative
information (valid formats: 'mzTab
')
-calculate_id_purity Calculate the purity of the precurs
or ion based on the MS1 spectrum.
Only used for MS3, otherwise it is
the same as the quant. precursor
purity.
-psm_score <score> The score which should be reached
by a peptide hit to be kept. (use
'NAN' to disable this filter) (defa
ult: 'NaN')
-protein_score <score> The score which should be reached
by a protein hit to be kept. All
proteins are filtered based on thei
r singleton scores irrespective of
grouping. Use in combination with
'delete_unreferenced_peptide_hits'
to remove affected peptides. (use
'NAN' to disable this filter) (defa
ult: 'NaN')
-delete_unreferenced_peptide_hits Peptides not referenced by any prot
ein are deleted in the IDs.
-inference_method <option> Methods used for protein inference
(default: 'aggregation') (valid:
'aggregation', 'bayesian')
-proteinFDR <threshold> Protein FDR threshold (0.05=5%).
(default: '1.0') (min: '0.0' max:
'1.0')
-psmFDR <threshold> FDR threshold for sub-protein level
(e.g. 0.05=5%). (default: '1.0')
(min: '0.0' max: '1.0')
ProteinQuantification:
-ProteinQuantification:method <choice> - top - quantify based on three
most abundant peptides (number can
be changed in 'top').
- iBAQ (intensity based absolute
quantification), calculate the sum
of all peptide peak intensities
divided by the number of theoretica
lly observable tryptic peptides
...
input is allowed! (default: 'top')
(valid: 'top', 'iBAQ')
-ProteinQuantification:best_charge_and_fraction Distinguish between fraction and
charge states of a peptide. For
peptides, abundances will be report
ed separately for each fraction
and charge;
for proteins, abundances will be
computed based only on the most
prevalent charge observed of each
...
over all charge states.
Additional options for custom quantification using top N peptides.:
-ProteinQuantification:top:N <number> Calculate protein abundance from
this number of proteotypic peptides
(most abundant first; '0' for all)
(default: '3') (min: '0')
-ProteinQuantification:top:aggregate <choice> Aggregation method used to compute
protein abundances from peptide
abundances (default: 'median') (val
id: 'median', 'mean', 'weighted_mea
n', 'sum')
Additional options for consensus maps (and identification results comprising multiple runs):
-ProteinQuantification:consensus:normalize Scale peptide abundances so that
medians of all samples are equal
-ProteinQuantification:consensus:fix_peptides Use the same peptides for protein
quantification across all samples.
With 'N 0',all peptides that occur
in every sample are considered.
Otherwise ('N'), the N peptides
that occur in the most samples (ind
ependently of each other) are selec
ted,
...
n!).
BasicProteinInference:
-BasicProteinInference:min_peptides_per_protein <number> Minimal number of peptides needed
for a protein identification. If
set to zero, unmatched proteins
get a score of -Infinity. If bigger
than zero, proteins with less pept
ides are filtered and evidences
removed from the PSMs. PSMs that
do not reference any proteins anymo
re are removed but the spectrum
info is kept. (default: '1') (min:
'0')
-BasicProteinInference:score_aggregation_method <choice> How to aggregate scores of peptides
matching to the same protein? (def
ault: 'best') (valid: 'best', 'prod
uct', 'sum', 'maximum')
-BasicProteinInference:treat_charge_variants_separately <choice> If this is true, different charge
variants of the same peptide sequen
ce count as individual evidences.
(default: 'true') (valid: 'true',
'false')
-BasicProteinInference:treat_modification_variants_separately <choice> If this is true, different modifica
tion variants of the same peptide
sequence count as individual eviden
ces. (default: 'true') (valid: 'tru
e', 'false')
-BasicProteinInference:use_shared_peptides <choice> If this is true, shared peptides
are used as evidences. Note: shared
_peptides are not deleted and poten
tially resolved in postprocessing
as well. (default: 'true') (valid:
'true', 'false')
-BasicProteinInference:skip_count_annotation If this is set, peptide counts won'
t be annotated at the proteins.
-BasicProteinInference:score_type <choice> PSM score type to use for inference
. (default: empty = main score)
(valid: '', 'PEP', 'q-value', 'RAW'
)
BayesianProteinInference:
-BayesianProteinInference:psm_probability_cutoff <value> Remove PSMs with probabilities less
than this cutoff (default: '1.0e-0
3') (min: '0.0' max: '1.0')
-BayesianProteinInference:top_PSMs <number> Consider only top X PSMs per spectr
um. 0 considers all. (default: '1')
(min: '0')
Common TOPP options:
-ini <file> Use the given TOPP INI file
-threads <n> Sets the number of threads allowed
to be used by the TOPP tool (defaul
t: '1')
-write_ini <file> Writes the default configuration
file
--help Shows options
--helphelp Shows all options (including advanc
ed)
The following configuration subsections are valid:
- extraction Parameters for the channel extraction.
- itraq4plex Algorithm parameters for iTRAQ 4-plex
- itraq8plex Algorithm parameters for iTRAQ 8-plex
- quantification Parameters for the peptide quantification.
- tmt10plex Algorithm parameters for TMT 10-plex
- tmt11plex Algorithm parameters for TMT 11-plex
- tmt16plex Algorithm parameters for TMT 16-plex
- tmt18plex Algorithm parameters for TMT 18-plex
- tmt6plex Algorithm parameters for TMT 6-plex
You can write an example INI file using the '-write_ini' option.
Documentation of subsection parameters can be found in the doxygen documentation or the INIFileEditor.
For more information, please consult the online documentation for this tool:
- http://www.openms.de/doxygen/nightly/html/TOPP_IsobaricWorkflow.html
INI file documentation of this tool: