Solution structure of the PHD domain from the KAP‐1 corepressor: structural determinants for PHD, RING and LIM zinc‐binding domains

Plant homeodomain (PHD) domains are found in >400 eukaryotic proteins, many of which are transcriptional regulators. Naturally occurring point mutations or deletions of this domain contribute to a variety of human diseases, including ATRX syndrome, myeloid leukemias and autoimmune dysfunction. Here we report the first structural characterization of a PHD domain. Our studies reveal that the PHD domain from KAP‐1 corepressor binds zinc in a cross‐brace topology between anti‐parallel β‐strands reminiscent of RING (really interesting new gene) domains. Using a mutational analysis, we define the structural features required for transcriptional repression by KAP‐1 and explain naturally occurring, disease‐causing mutations in PHD domains of other proteins. From a comparison of this PHD structure with previously reported RING and LIM (Lin11/Isl‐1/Mec‐3) structures, we infer sequence determinants that allow discrimination among PHD, RING and LIM motifs.