Effect of charge on the conformation of highly basic peptides including the tail regions of histone proteins by ion mobility mass spectrometry
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The first systematic and comprehensive study of the charging behaviour and effect of charge on the conformation of specifically constructed arginine-rich peptides and its significance to the N- and C-terminal basic tail regions of histone proteins was conducted using ion mobility mass spectrometry (IM-MS). Among the basic amino acids, arginine has the greatest impact on the charging behaviour and structures of gas phase ions by virtue of its high proton affinity. A close linear correlation was found between either the maximum charge, or most abundant charge state, that the peptides support and their average collision cross section (CCS) values measured by ion mobility mass spectrometry. The calculated collision cross sections for the lowest energy solution state models predicted by the PEP-FOLD algorithm using a modified MOBCAL trajectory method were found to best correlate with the values measured by IM-MS. In the case of the histone peptides, more compact folded structures, supporting less than the maximum number of charges, were observed. These results are consistent with those previously reported for histone dimers where neutralization of the charge at the basic residues of the tail regions did not affect their CCS values.
KeywordsPeptide Charge Conformation Structure Ion mobility Mass spectrometry
The Waters Synapt G2 ion mobility mass spectrometer used in these investigations was purchased with funds provided by a Grant-in-Aid for Scientific Research in Innovative Areas (21113003) (to S. Akashi) from the Ministry of Education, Culture, Sports, Science and Technology, Japan. The authors are grateful to Prof. Hajime Tanuma (Tokyo Metropolitan University) who provided an algorithm that allowed for the calculation of peptide theoretical collision cross sections (CCS) in nitrogen gas. The authors thank Asst. Prof. Kazumi Saikusa (Hiroshima University) who implemented the algorithm and helped with their calculation.
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Conflict of interest
The authors declare that they have no conflict of interest.
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