Mass Spectrometric Analysis of Histone Proteoforms

Histones play important roles in chromatin, in the forms of various posttranslational modifications (PTMs) and sequence variants, which are called histone proteoforms. Investigating modifications and variants is an ongoing challenge. Previous methods are based on antibodies, and because they usually detect only one modification at a time, they are not suitable for studying the various combinations of modifications on histones. Fortunately, mass spectrometry (MS) has emerged as a high-throughput technology for histone analysis and does not require prior knowledge about any modifications. From the data generated by mass spectrometers, both identification and quantification of modifications, as well as variants, can be obtained easily. On the basis of this information, the functions of histones in various cellular contexts can be revealed. Therefore, MS continues to play an important role in the study of histone proteoforms. In this review, we discuss the analysis strategies of MS, their applications on histones, and some key remaining challenges.