Beyond linker histones and high mobility group proteins: Global profiling of perchloric acid soluble proteins

Extraction with HClO4 provides an easy method for efficient enrichment of both histone H1 and HMG proteins from a variety of tissues. Usually, the histone and the HMG proteins are the most abundant components of the extracts, however, other proteins have frequently been observed but only seldom studied in more detail. Here we describe a study aimed at global characterization of HClO4 extractable proteins from breast cancer cell lines. We report identification of 150 unique proteins by liquid chromatography tandem mass spectrometry including almost all major histone H1 variants and canonical members of the HMG protein families. In the extracts, diverse proteins with HMG-like amino acid composition were identified and their post-translational modifications were mapped. Importantly, those include multiple proteins known or supposed to be related to cell proliferation and cancer. Since purification of these proteins as well as low abundant variants of histone and HMG proteins is difficult due to their metabolic instability, characterization of these proteins from crude extracts can facilitate studies aimed at better understanding of their function.