Solution structure of a multifunctional DNA- and protein-binding motif of human Werner syndrome protein

Werner syndrome (WS) is an autosomal recessive disease that results in premature aging. Mutations in the WS gene (WRN) result in a loss of expression of the WRN protein and predispose WS patients to accelerated aging. As a helicase and a nuclease, WRN is unique among the five human RecQ helicase family members and is capable of multiple functions involved in DNA replication, repair, recombination, and telomere maintenance. A 144-residue fragment of WRN was previously determined to be a multifunctional DNA- and protein-binding domain (DPBD) that interacts with structure-specific DNA and a variety of DNA-processing proteins. In addition, DPBD functions as a nucleolar targeting sequence of WRN. The solution structure of the DPBD, the first of a WRN fragment, has been solved by NMR. DPBD consists of a winged helix-like motif and an unstructured C-terminal region of approximately 20 aa. The putative DNA-binding surface of DPBD has been identified by using known structural and biochemical data. Based on the structural data and on the biochemical data, we suggest a surface on the DPBD for interacting with other proteins. In this structural model, a single winged helix domain binds to both DNA and other proteins. Furthermore, we propose that DPBD functions as a regulatory domain to regulate the enzymatic activity of WRN and to direct cellular localization of WRN through protein-protein interaction.