FAST LiH DESTRUCTION IN REACTION WITH H: QUANTUM CALCULATIONS AND ASTROPHYSICAL CONSEQUENCES

We present a quantum-mechanical study of the exothermic (7)LiH reaction with H. Accurate reactive probabilities and rate coefficients are obtained by solving the Schrodinger equation for the motion of the three nuclei on a single Born-Oppenheimer potential energy surface and using a coupled-channel hyperspherical coordinate method. Our new rates indeed confirm earlier, qualitative predictions and some previous theoretical calculations, as discussed in the main text. In the astrophysical domain, we find that the depletion process largely dominates for redshift (z) between 400 and 100, a range significant for early universe models. This new result from first-principle calculations leads us to definitively surmise that LiH should be already destroyed when the survival processes become important. Because of this very rapid depletion reaction, the fractional abundance of LiH is found to be drastically reduced, so that it should be very difficult to manage to observe it as an imprinted species in the cosmic background radiation. The present findings appear to settle the question of LiH observability in the early universe. We further report several state-to-state computed reaction rates in the same range of temperatures of interest for the present problem

Structure of the helicase core of Werner helicase, a key target in microsatellite instability cancers

Loss of WRN, a DNA repair helicase, was identified as a strong vulnerability of microsatellite instable (MSI) cancers, making WRN a promising drug target. We show that ATP binding and hydrolysis are required for genome integrity and viability of MSI cancer cells. We report a 2.2-Å crystal structure of the WRN helicase core (517–1,093), comprising the two helicase subdomains and winged helix domain but not the HRDC domain or nuclease domains. The structure highlights unusual features. First, an atypical mode of nucleotide binding that results in unusual relative positioning of the two helicase subdomains. Second, an additional β-hairpin in the second helicase subdomain and an unusual helical hairpin in the Zn2+ binding domain. Modelling of the WRN helicase in complex with DNA suggests roles for these features in the binding of alternative DNA structures. NMR analysis shows a weak interaction between the HRDC domain and the helicase core, indicating a possible biological role for this association. Together, this study will facilitate the structure-based development of inhibitors against WRN helicase