title: Crystal structure of conserved domains 1 and 2 of the human DEAD-box helicase DDX3X in complex with the mononucleotide AMP.
abstract: DExD-box helicases are involved in all aspects of cellular RNA metabolism. Conserved domains 1 and 2 contain nine signature motifs that are responsible for nucleotide binding, RNA binding and ATP hydrolysis. The human DEAD-box helicase DDX3X has been associated with several different cellular processes, such as cell-growth control, mRNA transport and translation, and is suggested to be essential for the export of unspliced/partially spliced HIV mRNAs from the nucleus to the cytoplasm. Here, the crystal structure of conserved domains 1 and 2 of DDX3X, including a DDX3-specific insertion that is not generally found in human DExD-box helicases, is presented. The N-terminal domain 1 and the C-terminal domain 2 both display RecA-like folds comprising a central beta-sheet flanked by alpha-helices. Interestingly, the DDX3X-specific insertion forms a helical element that extends a highly positively charged sequence in a loop, thus increasing the RNA-binding surface of the protein. Surprisingly, although DDX3X was crystallized in the presence of a large excess of ADP or the slowly hydrolyzable ATP analogue ATPgammaS the contaminant AMP was seen in the structure. A fluorescent-based stability assay showed that the thermal stability of DDX3X was increased by the mononucleotide AMP but not by ADP or ATPgammaS, suggesting that DDX3X is stabilized by AMP and elucidating why AMP was found in the nucleotide-binding pocket.
authors.affiliation: Structural Genomics Consortium, Department of Medical Biochemistry and Biophysics, Karolinska Institute, SE-171 77 Stockholm, Sweden.
authors.forename: Martin
authors.initials: M
authors.lastname: Högbom
authors.forename: Ruairi
authors.initials: R
authors.lastname: Collins
authors.forename: Susanne
authors.initials: S
authors.lastname: van den Berg
authors.forename: Rose-Marie
authors.initials: RM
authors.lastname: Jenvert
authors.forename: Tobias
authors.initials: T
authors.lastname: Karlberg
authors.forename: Tetyana
authors.initials: T
authors.lastname: Kotenyova
authors.forename: Alex
authors.initials: A
authors.lastname: Flores
authors.forename: Gunilla B
authors.initials: GB
authors.lastname: Karlsson Hedestam
authors.forename: Lovisa Holmberg
authors.initials: LH
authors.lastname: Schiavone
mesh_terms: D000249:Adenosine Monophosphate / Q000737:chemistry* / Q000378:metabolism*; D000255:Adenosine Triphosphate / Q000378:metabolism; D000595:Amino Acid Sequence; D001665:Binding Sites; D017124:Conserved Sequence; D018360:Crystallography, X-Ray; D053487:DEAD-box RNA Helicases / Q000737:chemistry* / Q000378:metabolism*; D004795:Enzyme Stability; D006801:Humans; D006868:Hydrolysis; D008958:Models, Molecular; D008969:Molecular Sequence Data; D017434:Protein Structure, Tertiary; D016601:RNA-Binding Proteins / Q000737:chemistry / Q000378:metabolism; D017386:Sequence Homology, Amino Acid
chemical_list: D016601:RNA-Binding Proteins; D000249:Adenosine Monophosphate; D000255:Adenosine Triphosphate; C119332:DDX3X protein, human; D053487:DEAD-box RNA Helicases