Recognition and coacervation of G-quadruplexes by a multifunctional disordered region in RECQ4 helicase

Biomolecular polyelectrolyte complexes can be formed between oppositely charged intrinsically disordered regions (IDRs) of proteins or between IDRs and nucleic acids. Highly charged IDRs are abundant in the nucleus, yet few have been functionally characterized. Here, we show that a positively charged IDR within the human ATP-dependent DNA helicase Q4 (RECQ4) forms coacervates with G-quadruplexes (G4s). We describe a three-step model of charge-driven coacervation by integrating equilibrium and kinetic binding data in a global numerical model. The oppositely charged IDR and G4 molecules form a complex in the solution that follows a rapid nucleation-growth mechanism leading to a dynamic equilibrium between dilute and condensed phases. We also discover a physical interaction with Replication Protein A (RPA) and demonstrate that the IDR can switch between the two extremes of the structural continuum of complexes. The structural, kinetic, and thermodynamic profile of its interactions revealed a dynamic disordered complex with nucleic acids and a static ordered complex with RPA protein. The two mutually exclusive binding modes suggest a regulatory role for the IDR in RECQ4 function by enabling molecular handoffs. Our study extends the functional repertoire of IDRs and demonstrates a role of polyelectrolyte complexes involved in G4 binding

BEER - The Beamline for European Materials Engineering Research at the ESS

The Beamline for European Materials Engineering Research (BEER) will be built at the European Spallation Source (ESS). The diffractometer utilizes the high brilliance of the long-pulse neutron source and offers high instrument flexibility. It includes a novel chopper technique that extracts several short pulses out of the long pulse, leading to substantial intensity gain of up to an order of magnitude compared to pulse shaping methods for materials with high crystal symmetry. This intensity gain is achieved without compromising resolution. Materials of lower crystal symmetry or multi-phase materials will be investigated by additional pulse shaping methods. The different chopper set-ups and advanced beam extracting techniques offer an extremely broad intensity/resolution range. Furthermore, BEER offers an option of simultaneous SANS or imaging measurements without compromising diffraction investigations. This flexibility opens up new possibilities for in-situ experiments studying materials processing and performance under operation conditions. To fulfil this task, advanced sample environments, dedicated to thermo-mechanical processing, are foreseen

Tensile deformation of NiTi shape memory alloy thermally loaded under applied stress

Constitutive behavior of engineering materials is typically characterized by stress–strain curves from isothermal tensile and/or compression tests until fracture. Strain reversible behavior of martensitically transforming shape memory alloys (SMA) is additionally characterized by cyclic stress–strain and strain-temperature curves limited to temperatures and stresses, at which the recorded strain responses are reversible in closed loop cycles. In this work focussing coupled martensitic transformation and plastic deformation of NiTi, we deformed nanocrystalline NiTi SMA wire in isothermal and isostress tensile tests beyond the temperature and stress limits stemming from the requirement on the strain reversibility in closed loop cyclic tests. Stress–strain-temperature responses of NiTi wire in such tests were recorded and analysed. To detect and characterize deformation mechanisms activated in performed thermomechanical loads, electric resistance and dynamic elastic modulus of the wire were evaluated in-situ during tensile tests. Martensite variant microstructures and lattice defects in austenite evolving upon heating deformed NiTi wire under 750 MPa stress were analyzed by post mortem transmission electron microscopy. Stress-temperature diagram showing critical stress–temperature conditions for activation of 5 different deformation/transformation processes in thermomechanically loaded NiTi was constructed from the results of isothermal and isostress tests and the recorded stress–strain-temperature responses were discussed based on this diagra