Identification of Phosphorylation Sites on Heterochromatin Protein 1 by Electron Transfer Dissociation

摘要

Phosphorylation of HP1alpha is upregulated during mitosis, and all detected phosphorylation sites are located in the less structured hinge region. What is the biological relevance of these phosphorylation sites? The hige region has been demonstrated to interact with INCENP, which is part of the Chromosomal Passenger Complex (CPC). Aurora B kinase is responsible for phosphorylating histone H3 on S10, which abolishes the HP1-H3 interaction; it is also part of the CPC. Could phosphorylation of HP1 be involved with regulating CPC function and localization? Does phosphorylation of HP1 occur before or after the start of mitosis? Also, immunoprecipitation of HP1a-FLAG fusion protein also pulls down HP1 beta and gama isoforms with it, thus agreeing with evidence for HP1 heterodimerization through the chromo shadow domain. Lastly, fragmentation by ETD greatly enhances peptide sequence coverage and improves phosphosite identification.