The intrinsically disordered amino-terminal region of human RecQL4: multiple DNA-binding domains confer annealing, strand exchange and G4 DNA binding.

Human RecQL4 belongs to the ubiquitous RecQ helicase family. Its N-terminal region represents the only homologue of the essential DNA replication initiation factor Sld2 of Saccharomyces cerevisiae, and also participates in the vertebrate initiation of DNA replication. Here, we utilized a random screen to identify N-terminal fragments of human RecQL4 that could be stably expressed in and purified from Escherichia coli. Biophysical characterization of these fragments revealed that the Sld2 homologous RecQL4 N-terminal domain carries large intrinsically disordered regions. The N-terminal fragments were sufficient for the strong annealing activity of RecQL4. Moreover, this activity appeared to be the basis for an ATP-independent strand exchange activity. Both activities relied on multiple DNA-binding sites with affinities to single-stranded, double-stranded and Y-structured DNA. Finally, we found a remarkable affinity of the N-terminus for guanine quadruplex (G4) DNA, exceeding the affinities for other DNA structures by at least 60-fold. Together, these findings suggest that the DNA interactions mediated by the N-terminal region of human RecQL4 represent a central function at the replication fork. The presented data may also provide a mechanistic explanation for the role of elements with a G4-forming propensity identified in the vicinity of vertebrate origins of DNA replication.

Two Pseudopolymorphic Star-Shaped Tetranuclear Co(3+) Compounds with Disulfide Anions Exhibiting Two Different Connection Modes and Promising Photocatalytic Properties.

The compound [Co4(C6H14N2)4(µ4-S2)2(µ2-S2)4] (I) and the pseudo-polymorph [Co4(C6H14N2)4(µ4-S2)2(µ2-S2)4]⋅4 H2O (II) were obtained under solvothermal conditions (C6H14N2=trans-1,2-diaminocyclohexane). The structures feature S2(2-) ions exhibiting two different coordination modes. Terminal S2(2-) entities join two Co(3+) centres in a µ2 fashion, whereas the central S2(2-) groups connect four Co(3+) cations in a µ4-coordination mode. Compound II can be transformed into compound I by heat and storage over P2O5 and storing compound I in humid air yields in the formation of compound II. The intermolecular interactions investigated through Hirshfeld surface analysis reveal that besides S⋅⋅⋅H bonding close contacts are associated with relatively weak H⋅⋅⋅H interactions. A detailed DFT analysis of the bonding situation explains the long S-S bonds in the µ4-bridging S2(2-) units and the short bonds for the S2(2-) moieties in the µ2-connecting mode. Photocatalytic hydrogen evolution experiments demonstrate the potential of compound II as catalyst.

The N-terminus of the human RecQL4 helicase is a homeodomain-like DNA interaction motif.

The RecQL4 helicase is involved in the maintenance of genome integrity and DNA replication. Mutations in the human RecQL4 gene cause the Rothmund-Thomson, RAPADILINO and Baller-Gerold syndromes. Mouse models and experiments in human and Xenopus have proven the N-terminal part of RecQL4 to be vital for cell growth. We have identified the first 54 amino acids of RecQL4 (RecQL4_N54) as the minimum interaction region with human TopBP1. The solution structure of RecQL4_N54 was determined by heteronuclear liquid-state nuclear magnetic resonance (NMR) spectroscopy (PDB 2KMU; backbone root-mean-square deviation 0.73 Å). Despite low-sequence homology, the well-defined structure carries an overall helical fold similar to homeodomain DNA-binding proteins but lacks their archetypical, minor groove-binding N-terminal extension. Sequence comparison indicates that this N-terminal homeodomain-like fold is a common hallmark of metazoan RecQL4 and yeast Sld2 DNA replication initiation factors. RecQL4_N54 binds DNA without noticeable sequence specificity yet with apparent preference for branched over double-stranded (ds) or single-stranded (ss) DNA. NMR chemical shift perturbation observed upon titration with Y-shaped, ssDNA and dsDNA shows a major contribution of helix α3 to DNA binding, and additional arginine side chain interactions for the ss and Y-shaped DNA.

Extravascular lung water index and Halperin score to predict outcome in critically ill patients.

OBJECTIVE: The aim of this study was to describe real world extravascular lung water index (EVLWI) measurements obtained by pulse index continuous cardiac output (PiCCO) on the day of admission. These were then related to a radiologic score for lung edema, Halperin score and both the Halperin score and EVLWI were assessed for prediction of in-hospital mortality in critically ill patients. METHODS AND RESULTS: A total of 311 patients admitted to a tertiary medical university hospital between February 2004 and December 2010 were included in this retrospective analysis and of these 177 patients were intubated. In-hospital mortality was assessed by logistic regression. In the overall cohort, EVLWI and the Halperin score correlated poorly (r = 0.17; p = 0.02). In intubated patients, EVLWI and Halperin score did not correlate (r = 0.09; p = 0.39), whereas in patients who were not intubated there was a moderate association (r = 0.30; p = 0.007). In the overall cohort, (a) EVLWI (hazard ratio [HR] 1.10, 95% confidence interval [CI] 1.02-1.19; p = 0.01; area under the curve [AUC] 0.63, 95% CI 0.54-0.71) but not (b) Halperin score (HR 1.00, 95% CI 0.996-1.004; p = 0.94; AUC 0.52, 95% CI 0.45-0.58) was associated with in-hospital mortality There was a robust association of EVLWI (HR 1.12, 95% CI 1.01-1.25; p = 0.03) but not Halperin score (HR 1.003, 95% CI 0.997-1.009; p = 0.30) with mortality in non-intubated patients. In intubated patients, neither EVLWI (HR 0.997 95% CI 0.990-1.003; p = 0.33) nor Halperin score (HR 1.08; 95% CI 0.88-1.32; p = 0.47) was associated with mortality. CONCLUSION: The EVLWI correlated moderately with a radiologic score for lung edema, the Halperin score, in non-intubated but not in intubated patients. The EVLWI at admission was associated with in-hospital mortality in our patient collective of critically ill patients and might constitute not only a tool for risk stratification but most importantly a valuable treatment goal.

Tuneable anisotropy and magnetism in Sn2Co3S2-xSex - probed by (119)Sn Mößbauer spectroscopy and DFT studies.

The half metal (HFM) Sn2Co3S2 shows a fascinating S = 1/2 magnetism. Anisotropic coupling of spins in and between Co Kagomé layers by Sn sites is now studied from the substitution effects of S by Se by systematic and local experimental and first principles data. Trends in crystal structure changes (c/a ratio) as retrieved from XRD data on the solid solution Sn2Co3S2-xSex are complemented by DFT modelling on Sn2Co3SeS and hitherto unknown Sn2Co3Se2. The relationship of crystal structure effects with changes in Curie temperatures and magnetic hysteresis is shown from susceptibility measurements. An insight into the role of the Sn sites in magnetism and bonding is gained from (119)Sn Mössbauer spectroscopic measurements. Isomer shifts, quadrupole splitting, and magnetic hyperfine fields are interpreted by DFT calculations on chemical bonding, electric field gradients (EFG), Fermi contact, and spin polarization.

Conformational signatures of 13C chemical shifts in RNA ribose.

The conformational dependence of (13)C chemical shift values of RNA riboses determined by liquid-state NMR spectroscopy was evaluated using data deposited for RNA structures in the RCSD and BMRB data bases. Results derived support the applicability of the canonical coordinates approach of Rossi and Harbison (J Magn Reson 151:1-8, 2001) in liquid-state NMR to assess the sugar pucker of ribose units in RNA.