Now showing 1 - 5 of 15
- ItemHuman DDX17 unwinds Rift Valley fever virus non-coding RNAs(MDPI, 2020) Nelson, Corey R.; Mrozowich, Tyler; Park, Sean M.; D'Souza, Simmone; Henrickson, Amy; Vigar, Justin R. J.; Wieden, Hans-Joachim; Owens, Raymond J.; Demeler, Borries; Patel, Trushar R.Rift Valley fever virus (RVFV) is a mosquito-transmitted virus from the Bunyaviridae family that causes high rates of mortality and morbidity in humans and ruminant animals. Previous studies indicated that DEAD-box helicase 17 (DDX17) restricts RVFV replication by recognizing two primary non-coding RNAs in the S-segment of the genome: the intergenic region (IGR) and 5′ non-coding region (NCR). However, we lack molecular insights into the direct binding of DDX17 with RVFV non-coding RNAs and information on the unwinding of both non-coding RNAs by DDX17. Therefore, we performed an extensive biophysical analysis of the DDX17 helicase domain (DDX17135–555) and RVFV non-coding RNAs, IGR and 5’ NCR. The homogeneity studies using analytical ultracentrifugation indicated that DDX17135–555, IGR, and 5’ NCR are pure. Next, we performed small-angle X-ray scattering (SAXS) experiments, which suggested that DDX17 and both RNAs are homogenous as well. SAXS analysis also demonstrated that DDX17 is globular to an extent, whereas the RNAs adopt an extended conformation in solution. Subsequently, microscale thermophoresis (MST) experiments were performed to investigate the direct binding of DDX17 to the non-coding RNAs. The MST experiments demonstrated that DDX17 binds with the IGR and 5’ NCR with a dissociation constant of 5.77 ± 0.15 µM and 9.85 ± 0.11 µM, respectively. As DDX17135–555 is an RNA helicase, we next determined if it could unwind IGR and NCR. We developed a helicase assay using MST and fluorescently-labeled oligos, which suggested DDX17135–555 can unwind both RNAs. Overall, our study provides direct evidence of DDX17135–555 interacting with and unwinding RVFV non-coding regions
- ItemCellular roles of the human Obg-like ATPase 1 (hOLA1) and its YchF homologs(Canadian Science Publishing, 2020) Balasingam, Nirujah; Brandon, Harland E.; Ross, Joseph A.; Wieden, Hans-Joachim; Thakor, NehalP-loop NTPases comprise one of the major superfamilies of nucleotide binding proteins, which mediate a variety of cellular processes, such as mRNA translation, signal transduction, cell motility, and growth regulation. In this review, we discuss the structure and function of two members of the ancient Obg-related family of P-loop GTPases: human Obg-like ATPase 1 (hOLA1), and its bacterial/plant homolog, YchF. After a brief discussion of nucleotide binding proteins in general and the classification of the Obg-related family in particular, we discuss the sequence and structural features of YchF and hOLA1. We then explore the various functional roles of hOLA1 in mammalian cells during stress response and cancer progression, and of YchF in bacterial cells. Finally, we directly compare and contrast the structure and function of hOLA1 with YchF before summarizing the future perspectives of hOLA1 research. This review is timely, given the variety of recent studies aimed at understanding the roles of hOLA1 and YchF in such critical processes as cellular-stress response, oncogenesis, and protein synthesis.
- ItemCharacterization of fluorescein arsenical hairpin (FIAsH) as a probe for single-molecule fluorescence spectroscopy(Nature Research, 2017) Fernandes, Dennis D.; Bamrah, Jasbir; Kailasam, Senthilkumar; Gomes, Gregory-Neal W.; Li, Yuchong; Wieden, Hans-Joachim; Gradinaru, Claudiu C.In recent years, new labelling strategies have been developed that involve the genetic insertion of small amino-acid sequences for specific attachment of small organic fluorophores. Here, we focus on the tetracysteine FCM motif (FLNCCPGCCMEP), which binds to fluorescein arsenical hairpin (FlAsH), and the ybbR motif (TVLDSLEFIASKLA) which binds fluorophores conjugated to Coenzyme A (CoA) via a phosphoryl transfer reaction. We designed a peptide containing both motifs for orthogonal labelling with FlAsH and Alexa647 (AF647). Molecular dynamics simulations showed that both motifs remain solvent-accessible for labelling reactions. Fluorescence spectra, correlation spectroscopy and anisotropy decay were used to characterize labelling and to obtain photophysical parameters of free and peptide-bound FlAsH. The data demonstrates that FlAsH is a viable probe for single-molecule studies. Single-molecule imaging confirmed dual labeling of the peptide with FlAsH and AF647. Multiparameter single-molecule Förster Resonance Energy Transfer (smFRET) measurements were performed on freely diffusing peptides in solution. The smFRET histogram showed different peaks corresponding to different backbone and dye orientations, in agreement with the molecular dynamics simulations. The tandem of fluorophores and the labelling strategy described here are a promising alternative to bulky fusion fluorescent proteins for smFRET and single-molecule tracking studies of membrane proteins.
- ItemA conserved P-loop anchor limits the structural dynamics that mediate nucleotide dissociation in EF-Tu(Nature Research, 2015) Mercier, Evan; Girodat, Dylan; Wieden, Hans-JoachimThe phosphate-binding loop (P-loop) is a conserved sequence motif found in mononucleotide-binding proteins. Little is known about the structural dynamics of this region and its contribution to the observed nucleotide binding properties. Understanding the underlying design principles is of great interest for biomolecular engineering applications. We have used rapid-kinetics measurements in vitro and molecular dynamics (MD) simulations in silico to investigate the relationship between GTP-binding properties and P-loop structural dynamics in the universally conserved Elongation Factor (EF) Tu. Analysis of wild type EF-Tu and variants with substitutions at positions in or adjacent to the P-loop revealed a correlation between P-loop flexibility and the entropy of activation for GTP dissociation. The same variants demonstrate more backbone flexibility in two N-terminal amino acids of the P-loop during force-induced EF-Tu-GTP dissociation in Steered Molecular Dynamics simulations. Amino acids Gly18 and His19 are involved in stabilizing the P-loop backbone via interactions with the adjacent helix C.We propose that these P-loop/helix C interactions function as a conserved P-loop anchoring module and identify the presence of P-loop anchors within several GTPases and ATPases suggesting their evolutionary conservation.
- ItemIdentification of two structural elements important for ribosome-dependent GTPase activity of elongation factor 4 (EF4/LepA)(Nature Research, 2015) De Laurentiis, Evelina I.; Wieden, Hans-JoachimThe bacterial translational GTPase EF4/LepA is structurally similar to the canonical elongation factor EF-G. While sharing core structural features with other translational GTPases, the function of EF4 remains unknown. Recent structural data locates the unique C-terminal domain (CTD) of EF4 in proximity to the ribosomal peptidyl transferase center (PTC). To investigate the functional role of EF4’s CTD we have constructed three C-terminal truncation variants.These variants are fully functional with respect to binding mant-GTP and mant-GDP as determined by rapid kinetics, as well as their intrinsic multiple turnover GTPase activity. Furthermore, they are able to form stable complexes with the 70S ribosome and 50S/30S ribosomal sub units.However,successive removal of the C-terminus impairs ribosome-dependent multiple turnover GTPase activity of EF4, which for the full-length protein is very similar to EF-G. Our findings suggest that the last 44 C-terminal amino acids of EF4 form a sub-domain within the C-terminal domain that is important for GTP-dependent function on the ribosome. Additionally, we show that efficient nucleotide hydrolysis by EF4 on the ribosome depends on a conserved histidine (His 81), similar to EF-G and EF-Tu.