Identification and structural characterization of a CBP/p300-binding domain from the ETS family transcription factor GABP alpha.

Using NMR spectroscopy, we identified and characterized a previously unrecognized structured domain near the N-terminus (residues 35-121) of the ETS family transcription factor GABP alpha. The monomeric domain folds as a five-stranded beta-sheet crossed by a distorted helix. Although globally resembling ubiquitin, the GABP alpha fragment differs in its secondary structure topology and thus appears to represent a new protein fold that we term the OST (On-SighT) domain. The surface of the GABP alpha OST domain contains two predominant clusters of negatively-charged residues suggestive of electrostatically driven interactions with positively-charged partner proteins. Following a best-candidate approach to identify such a partner, we demonstrated through NMR-monitored titrations and glutathione S-transferase pulldown assays that the OST domain binds to the CH1 and CH3 domains of the co-activator histone acetyltransferase CBP/p300. This provides a direct structural link between GABP and a central component of the transcriptional machinery.