Screen of seventeen HDAC1 mutants for LSD1 trapping. Wild type (WT) HDAC, along with mutants with single point mutation of residues in the 11 Å active site channel (A), 14 Å channel (B), or selected mutants from both (C), were expressed as Flag-tagged proteins (HDAC1-F) in HEK293 cells. Cells were also incubated with SAHA (10 μM) for 24 hr to increase robust acetylation. After lysis, proteins in the lysates were immunoprecipitated with anti-FLAG agarose beads, separated by SDS-PAGE, and western blot analyzed with Flag (top) or LSD1 (bottom) antibodies. As an expression control, proteins in lysates were also separated by SDS-PAGE and visualized with a LSD1 antibody. Repetitive trials are provided in supplementary Figures S1-S3.