Structure-based identification of a novel NTPase from Methanococcus jannaschii

Almost half of the entire set of predicted genomic products from Methanococ cus jannaschii are classified as functionally unknown hypothetical proteins . We present a structure-based identification of the biochemical function o f a protein with an as yet unknown function from a M. jannaschii gene, Mj02 26. The crystal structure of Mj0226 protein determined at 2.2 Angstrom, res olution reveals that the protein is a homodimer and each monomer folds into an elongated alpha/beta structure of a new ford family. Comparisons of Mj0 226 protein with protein structures in the database, however, indicate that one part of the protein is homologous to some of the nucleotide-binding pr oteins. Biochemical analysis shows that Mj0226 protein is a novel nucleotid e triphosphatase that can efficiently hydrolyze nonstandard nucleotides suc h as XTP to XMP or ITP to IMP, but not the standard nucleotides, in the pre sence of Mg2+ or Mn2+ ions.