The hypertrehalosemic neuropeptides of cicadas are structural isomers—evidence by ion mobility mass spectrometry
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It has been known for more than 20 years that the neurosecretory glands of the cicadas, the corpora cardiaca, synthesize two isobaric peptides with hypertrehalosemic activity. Both decapeptides have exactly the same amino acid sequence (pGlu-Val-Asn-Phe-Ser-Pro-Ser-Trp-Gly-Asn-NH2) and mass but differ in their retention time in reversed-phase liquid chromatography. A synthetic peptide with the same sequence elutes together with the second more hydrophobic peptide peak of the natural cicada extract. It is not clear what modification is causing the described observations. Therefore, in the current study, ion mobility separation in conjunction with high-resolution mass spectrometry was used to investigate this phenomenon as it was sensitive to changes in conformation. It detected different drift times in buffer gas for both the intact peptides and some of their fragment ions. Based on the ion mobility and fragment ion intensity of the corresponding ions, it is concluded that the region Pro6-Ser7-Trp8 contains a structural feature differing from the L-amino acids present in the known peptide. Whether the conformer is the result of racemization or other biochemical processes needs to be further investigated.
KeywordsIon mobility mass spectrometry AKH Conformation Isomer
Ion mobility separation
Matrix-assisted laser desorption
Reversed-phase liquid chromatography
Compliance with ethical standards
Conflict of interest
The authors declare that they have no conflict of interest.
All applicable international, national and/or institutional guidelines for the care and use of animals were followed. This article does not contain any studies with human participants performed by any of the authors.
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