NMR studies of the POU-specific DNA-binding domain of Oct-1: Sequential 1H and 15N assignments and secondary structure

The 1H and 15N resonances of the POU-specific DNA-binding domain of transcription factor Oct-1 have been assigned sequentially using two- dimensional homo- and heteronuclear NMR techniques, as well as three- dimensional heteronuclear NMR techniques, including TOCSY, 2D NOE, and NOESY- HMQC experiments. A number of typical short- and medium-range NOE contacts, as well as amide proton exchange data, gave evidence for the presence of four α-helices, in the peptide segments 1-19, 23-34, 40-49, and 54-71, which are connected by short loops of irregular structure. Interestingly, the second helix contains three glycine residues and the fourth helix a proline in the middle of the helix. Although the regular pattern of hydrogen bonds in the fourth helix is interrupted, due to the absence of an amide proton in proline, the helix is remarkably stable. All four helices are amphipathic, which suggests a packing of the apolar sides of the helices in the folded structure of the protein.