The conserved PCET motifs of E2A and HEB bind the KIX domain of CBP/p300. (A) Sequence alignment of the PCET motifs from E2A, HEB, and E2-2. The ζ-φ-x-x-φ-φ consensus sequence is indicated, and numbering is in accordance to the native protein sequence. ζ indicates an acidic amino acid; φ, a bulky hydrophobic amino acid; and x, any amino acid. Conserved hydrophobic amino acid residues are colored yellow, acid residues red, and basic residues blue. (B) Representative binding curves showing the change in fluorescence anisotropy of 5-carboxyfluorescein tagged E2A-PCET (12-25) and HEB-PCET (11-24) peptides with increasing total concentration of KIX. (C) Overlay of ¹H-¹⁵N HSQC spectra of 0.4mM ¹⁵N-labeled HEB-PCET in the absence (black) and presence (red) of 0.75mM KIX in 20mM MES, pH 6.0. Resonances are labeled by position in full-length HEB. Lines connect the resonances of free PCET (black) and the corresponding resonance when bound to KIX (red). Asterisks identify resonances that arise from impurities in the sample. Inset: Plot of {¹H}-¹⁵N NOE values as a function of HEB-PCET residue number at 18.8 T.