FT-ICR-MS approach to monitor asparagine deamidation and its isomers products in collagen from ancient bones

Abstract

This project investigates the use of ultrahigh resolution mass spectrometry along with fragmentation techniques such as electron capture dissociation (ECD) and collisionally activated dissociation (CAD) to study deamidation of ancient bone, by using potential deamidation markers present in bovine collagen standards. With the application of these techniques, several marker peptides present in the digested protein standard of bovine collagen were successfully assigned. The sequences of these peptides correlated well with the reported sequences for bovine collagen in the literature. FT-ICR-MS was used to monitor deamidation of collagen by following a shift of +0.948 Da in the spectrum, resulting in a mass difference of 19 mDa from the 13C of the non-deamidated form and the 12C of the deamidated form, which can be difficult to assign due to overlap with the 13C isotopic distribution in peptides. The rate constants for the deamidation reaction were calculated, and the extent of deamidation before sample handling was determined. The methodology developed was then applied to collagen extracted from real bone samples, both modern and ancient, proving to be a useful method for monitoring asparagine deamidation before sample preparation. Differentiation of the isomers products of deamidation (aspartic and isoaspartic acid) were successfully assigned (where possible) using the diagnostic ions originated from their ECD spectra