Comparative structural analysis of human DEAD-box RNA helicases.

DEAD-box RNA helicases play various, often critical, roles in all processes where RNAs are involved. Members of this family of proteins are linked to human disease, including cancer and viral infections. DEAD-box proteins contain two conserved domains that both contribute to RNA and ATP binding. Despite recent advances the molecular details of how these enzymes convert chemical energy into RNA remodeling is unknown. We present crystal structures of the isolated DEAD-domains of human DDX2A/eIF4A1, DDX2B/eIF4A2, DDX5, DDX10/DBP4, DDX18/myc-regulated DEAD-box protein, DDX20, DDX47, DDX52/ROK1, and DDX53/CAGE, and of the helicase domains of DDX25 and DDX41. Together with prior knowledge this enables a family-wide comparative structural analysis. We propose a general mechanism for opening of the RNA binding site. This analysis also provides insights into the diversity of DExD/H- proteins, with implications for understanding the functions of individual family members.

Structural basis for the interaction between tankyrase-2 and a potent Wnt-signaling inhibitor.

We report two crystal structures of the PARP domain of human tankyrase-2 (TNKS2). Tankyrases are involved in fundamental cellular processes such as telomere homeostasis and Wnt signaling. The complex of TNKS2 with the potent inhibitor XAV939 provides insights into the molecular basis of the strong interaction and suggests routes for further development of tankyrase inhibitors.

Crystal structure of human RNA helicase A (DHX9): structural basis for unselective nucleotide base binding in a DEAD-box variant protein.

RNA helicases of the DExD/H-box superfamily are critically involved in all RNA-related processes. No crystal structures of human DExH-box domains had been determined previously, and their structures were difficult to predict owing to the low level of homology among DExH-motif-containing proteins from diverse species. Here we present the crystal structures of the conserved domain 1 of the DEIH-motif-containing helicase DHX9 and of the DEAD-box helicase DDX20. Both contain a RecA-like core, but DHX9 differs from DEAD-box proteins in the arrangement of secondary structural elements and is more similar to viral helicases such as NS3. The N-terminus of the DHX9 core contains two long alpha-helices that reside on the surface of the core without contributing to nucleotide binding. The RNA-polymerase-II-interacting minimal transactivation domain sequence forms an extended loop structure that resides in a hydrophobic groove on the surface of the DEIH domain. DHX9 lacks base-selective contacts and forms an unspecific but important stacking interaction with the base of the bound nucleotide, and our biochemical analysis confirms that the protein can hydrolyze ATP, guanosine 5'-triphosphate, cytidine 5'-triphosphate, and uridine 5'-triphosphate. Together, these findings allow the localization of functional motifs within the three-dimensional structure of a human DEIH helicase and show how these enzymes can bind nucleotide with high affinity in the absence of a Q-motif.

Crystal structure of the catalytic domain of human PARP2 in complex with PARP inhibitor ABT-888.

Poly-ADP-ribose polymerases (PARPs) catalyze transfer of ADP-ribose from NAD(+) to specific residues in their substrate proteins or to growing ADP-ribose chains. PARP activity is involved in processes such as chromatin remodeling, transcription control, and DNA repair. Inhibitors of PARP activity may be useful in cancer therapy. PARP2 is the family member that is most similar to PARP1, and the two can act together as heterodimers. We used X-ray crystallography to determine two structures of the catalytic domain of human PARP2: the complexes with PARP inhibitors 3-aminobenzamide and ABT-888. These results contribute to our understanding of structural features and compound properties that can be employed to develop selective inhibitors of human ADP-ribosyltransferases.

The DEXD/H-box RNA helicase DDX19 is regulated by an {alpha}-helical switch.

DEXD/H-box RNA helicases couple ATP hydrolysis to RNA remodeling by an unknown mechanism. We used x-ray crystallography and biochemical analysis of the human DEXD/H-box protein DDX19 to investigate its regulatory mechanism. The crystal structures of DDX19, in its RNA-bound prehydrolysis and free posthydrolysis state, reveal an alpha-helix that inserts between the conserved domains of the free protein to negatively regulate ATPase activity. This finding was corroborated by biochemical data that confirm an autoregulatory function of the N-terminal region of the protein. This is the first study describing crystal structures of a DEXD/H-box protein in its open and closed cleft conformations.

Crystal structure of the yeast eIF4A-eIF4G complex: an RNA-helicase controlled by protein-protein interactions.

Translation initiation factors eIF4A and eIF4G form, together with the cap-binding factor eIF4E, the eIF4F complex, which is crucial for recruiting the small ribosomal subunit to the mRNA 5' end and for subsequent scanning and searching for the start codon. eIF4A is an ATP-dependent RNA helicase whose activity is stimulated by binding to eIF4G. We report here the structure of the complex formed by yeast eIF4G's middle domain and full-length eIF4A at 2.6-A resolution. eIF4A shows an extended conformation where eIF4G holds its crucial DEAD-box sequence motifs in a productive conformation, thus explaining the stimulation of eIF4A's activity. A hitherto undescribed interaction involves the amino acid Trp-579 of eIF4G. Mutation to alanine results in decreased binding to eIF4A and a temperature-sensitive phenotype of yeast cells that carry a Trp579Ala mutation as its sole source for eIF4G. Conformational changes between eIF4A's closed and open state provide a model for its RNA-helicase activity.

The crystal structure of the carboxy-terminal domain of human translation initiation factor eIF5.

The carboxy-terminal domain (CTD) of eukaryotic initiation factor 5 (eIF5) plays a central role in the formation of the multifactor complex (MFC), an important intermediate for the 43 S pre-initiation complex assembly. The IF5-CTD interacts directly with the translation initiation factors eIF1, eIF2-beta, and eIF3c, thus forming together with eIF2 bound Met-tRNA(i)(Met) the MFC. In this work we present the high resolution crystal structure of eIF5-CTD. This domain of the protein is exclusively composed out of alpha-helices and is homologous to the carboxy-terminal domain of eIF2B-epsilon (eIF2Bepsilon-CTD). The most striking difference in the two structures is an additional carboxy-terminal helix in eIF5. The binding sites of eIF2-beta, eIF3 and eIF1 were mapped onto the structure. eIF2-beta and eIF3 bind to non-overlapping patches of negative and positive electrostatic potential, respectively.