A. HEK293 cells were co-transfected with CDKL5NLS (wild type "WT" or kinase-dead "KD" K42R mutant) and either FLAG-EP400 (left), FLAG-ELOA (middle) or FLAG-TTDN1 (right). 24 h later cells were incubated with H2O2 (500 µM) for 15 min before being harvested and lysed. Protein extracts were subjected to immunoprecipitation with anti-FLAG-agarose beads. Precipitates were subjected to SDS-PAGE and blotting with antibodies shown (bottom panels) or staining with Coomassie Brilliant Blue (top panels). The bands corresponding to the FLAG-tagged proteins were excised from the gels in A. and processed for mass spectrometric detection of relevant phospho-peptides. Three independent co-transfection experiments were done for every condition. 