Conformational characterization of full-length X-chromosome-linked inhibitor of apoptosis protein (XIAP) through an integrated approach

The X-chromosome-linked inhibitor of apoptosis protein (XIAP) is a multidomain protein whose main function is to block apoptosis by caspase inhibition. XIAP is also involved in other signalling pathways, including NF-κB activation and copper homeostasis. XIAP is overexpressed in tumours, potentiating cell survival and resistance to chemotherapeutics, and has therefore become an important target for the treatment of malignancy. Despite the fact that the structure of each single domain is known, the conformation of the full-length protein has never been determined. Here, the first structural model of the full-length XIAP dimer, determined by an integrated approach using nuclear magnetic resonance, small-angle X-ray scattering and electron paramagnetic resonance data, is presented. It is shown that XIAP adopts a compact and relatively rigid conformation, implying that the spatial arrangement of its domains must be taken into account when studying the interactions with its physiological partners and in developing effective inhibitors.

Compensating H+ and Li+ ions in quartz structural channels of the gold fields of Darasun ore field (Eastern Transbaikal, Russia): electron paramagnetic resonance data

The composition and diffusion mobility of the compensating ions in the quartz structural channels of the gold fields in the Darasun, Teremkinskoye, and Talatuy gold fields of the Darasun ore field were examined using the electron paramagnetic resonance method. The assessment of the properties and peculiarities of the ion distribution in quartz was based on their ability to participate in the neutralization of the electric charges of the structural defects occurring in the minerals. In this regard, the ion composition was evaluated by the ratio of the concentrations of the Ti-centers using various compensators. Their mobility was determined by the center formation rate during the quartz radiation exposure. The research demonstrated the availability of two major compensating ions, H+ and Li+, in the quartz structural channels of the gold fields in the Darasun ore field. The diffusion mobility of the H+ ions in the channels was observed to be 1–2 orders of magnitude higher than that of Li+. The correlation link between the compensating ions in the mineral and fluid compositions was not obtained based on the data analysis. A difference was identified between the ratio of the H+ and Li+ concentrations in the quartz structural channels of different fields. Further, the highest concentration of H+ ions and the lowest concentration of Li+ ions were recorded for the quartz in the Darasun field; the inverse correlation was observed for the quartz in the Talatuy field, which can be attributed to the mixing of the fluid gas component during the ore formation process. The electron paramagnetic resonance method can be used for the quantitative assessment of the degree of quartz dynamic recrystallization.

Magnetic behaviour of bimetallic layered phases M′0.2Mn0.8PS3·0.25 H2O (M′ = ZnII, CuII, NiII, CoII)

Electron paramagnetic resonance data permit to estimate the critical temperatures of the bimetallic phases that could not be clearly inferred from the magnetic susceptibility data.