Journal
PROTEOMICS
Volume 9, Issue 16, Pages 4063-4070Publisher
WILEY-V C H VERLAG GMBH
DOI: 10.1002/pmic.200900267
Keywords
Mass spectrometry; Post-translational modification; Protein sequencing; Technology
Funding
- Grants-in-Aid for Scientific Research [21510225] Funding Source: KAKEN
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We describe a mass spectrometric method for distinguishing between free and modified forms of the C-terminal carboxyl group of peptides and proteins, in combination with chemical approaches for the isolation of C-terminal peptides and site-specific derivatization of the C-terminal carboxyl group. This method could most advantageously be exploited to discriminate between peptides having C-terminal carboxyl groups in the free (COOH) and amide (CONH(2)) forms by increasing their mass difference from 1 to 14 Da by selectively converting the free carboxyl group into methylamide (CONHCH(3)). This method has been proven to be applicable to peptides containing aspartic and glutamic acids, because all the carboxyl groups except the C-terminal one are inert to derivatization, according to oxazolone chemistry. The efficiency of the method is illustrated by a comparison of the peaks of processed peptides obtained from a mixture of adrenomedullin, calcitonin, and BSA. Among these components of the mixture, only the C-terminal peptide of BSA exhibited the mass shift of 13 Da upon treatment, eventually unambiguously validating the C-terminal amide structures of adrenomedullin and calcitonin. The possibility of extending this method for the analysis of C-terminal PTMs is also discussed.
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