4. Conclusion
The library of tandem mass spectra originated from many
publications and our own experiments and consisted of 263 MSn
spectra (mainly MS2 spectra) of 59 cyclic peptides and a few
related compounds, was build for identification of toxins of this
group. The library was tested by means of cross-validation. Tests
demonstrated that the percentage of correct identifications based
on the best-match product ion mass spectra of ’unknowns’ and
references was 70% in a general case and 88% without defective/
‘one-dimension’ spectra, i.e. simple lists of m/z values. However,
incorporation of such spectra in the reference set of mass spectra
in the course of the library validation somewhat increased TPR
(up to 91%). So, the percentage of 88–91% is the principal estimate
for the overall performance of this library.
ESI-MS2 spectra appeared to be rather close to MALDI-ToF/ToF
fragment spectra. Therefore reference spectra of these two groups
may be to a large extent substitutable for one another. So, fragment-
ion variants of MALDI such as the LIFT technique used in this
research have a promise as general techniques of building mass
spectral libraries.
The consideration of the nature of false positive results shows
that this library provides not only a method of choice for identification
of individual cyclopeptides and also one for the group
recognition of individual classes of these toxins. The approach to
identification of cyclopeptides based on mass spectral librarymatching should be the most effective for abundant ‘known
unknown’ compounds. Here de novo identification methods and
related ones taken from genomics/proteomics (see Introduction)
are not required. Also, this database should be enlarged to reliably
determine relatively rare peptides. If this is not the case, the use of
the library in qualitative analysis of real-world samples leads to
group/ambiguous identification results or even no results.
Conflict of interest
There are no conflicts of interest.
Acknowledgement
Nadezhda Medvedeva is thanked for providing the extracts of
cyanobacterial strains.
4. Conclusion
The library of tandem mass spectra originated from many
publications and our own experiments and consisted of 263 MSn
spectra (mainly MS2 spectra) of 59 cyclic peptides and a few
related compounds, was build for identification of toxins of this
group. The library was tested by means of cross-validation. Tests
demonstrated that the percentage of correct identifications based
on the best-match product ion mass spectra of ’unknowns’ and
references was 70% in a general case and 88% without defective/
‘one-dimension’ spectra, i.e. simple lists of m/z values. However,
incorporation of such spectra in the reference set of mass spectra
in the course of the library validation somewhat increased TPR
(up to 91%). So, the percentage of 88–91% is the principal estimate
for the overall performance of this library.
ESI-MS2 spectra appeared to be rather close to MALDI-ToF/ToF
fragment spectra. Therefore reference spectra of these two groups
may be to a large extent substitutable for one another. So, fragment-
ion variants of MALDI such as the LIFT technique used in this
research have a promise as general techniques of building mass
spectral libraries.
The consideration of the nature of false positive results shows
that this library provides not only a method of choice for identification
of individual cyclopeptides and also one for the group
recognition of individual classes of these toxins. The approach to
identification of cyclopeptides based on mass spectral librarymatching should be the most effective for abundant ‘known
unknown’ compounds. Here de novo identification methods and
related ones taken from genomics/proteomics (see Introduction)
are not required. Also, this database should be enlarged to reliably
determine relatively rare peptides. If this is not the case, the use of
the library in qualitative analysis of real-world samples leads to
group/ambiguous identification results or even no results.
Conflict of interest
There are no conflicts of interest.
Acknowledgement
Nadezhda Medvedeva is thanked for providing the extracts of
cyanobacterial strains.
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