Diversity in structure and function of the Ets family PNT domains.

The PNT (or Pointed) domain, present within a subset of the Ets family of transcription factors, is structurally related to the larger group of SAM domains through a common tertiary arrangement of four alpha-helices. Previous studies have shown that, in contrast to the PNT domain from Tel, this domain from Ets-1 contains an additional N-terminal helix integral to its folded structure. To further investigate the structural plasticity of the PNT domain, we have used NMR spectroscopy to characterize this domain from two additional Ets proteins, Erg and GABPalpha. These studies both define the conserved and variable features of the PNT domain, and demonstrate that the additional N-terminal helix is also present in GABPalpha, but not Erg. In contrast to Tel and Yan, which self-associate to form insoluble polymers, we also show that the isolated PNT domains from Ets-1, Ets-2, Erg, Fli-1, GABPalpha, and Pnt-P2 are monomeric in solution. Furthermore, these soluble PNT domains do not associate in any pair-wise combination. Thus these latter Ets family PNT domains likely mediate interactions with additional components of the cellular signaling or transcriptional machinery.