Aronsson, Anna | Guler, Fatma | Petoukhov, Maxim V. | Crennell, Susan J. | Svergun, Dmitri I. | Linares-Pasten, Javier A. | Karlsson, Eva Nordberg

Article | 2018 | BIOCHIMICA ET BIOPHYSICA ACTA-PROTEINS AND PROTEOMICS1866 ( 2 ) , pp.292 - 306

Hydrolysis of arabinoxylan (AX) by glycoside hydrolase family 10 (GH10) xylanases produces xylo-and arabinoxylo-oligosaccharides ((A)XOS) which have shown prebiotic effects. The thermostable GH10 xylanase RmXyn10A has shown great potential to produce (A)XOS. In this study, the structure of RmXynlOA was investigated, the catalytic module by homology modelling and site-directed mutagenesis and the arrangement of its five domains by small-angle X-ray scattering (SAXS). Substrate specificity was explored in silico by manual docking and molecular dynamic simulations. It has been shown in the literature that the glycone subsites of GH10 x . . .ylanases are well conserved and our results suggest that RmXyn10A is no exception. The aglycone subsites are less investigated, and the modelled structure of RmXyn10A suggests that loop alpha(6)beta(6) in the aglycone part of the active site contains a non-conserved alpha-helix, which blocks the otherwise conserved space of subsite + 2. This structural feature has only been observed for one other GH10 xylanase. In RmXyn10A, docking revealed two alternative binding regions, one on either side of the alpha-helix. However, only one was able to accommodate arabinose-substitutions and the mutation study suggests that the same region is responsible for binding XOS. Several non-conserved structural features are most likely to be responsible for providing affinity for arabinose-substitutions in subsites +1 and + 2. The SAXS rigid model of the modular arrangement of RmXyn10A displays the catalytic module close to the cell-anchoring domain while the carbohydrate binding modules are further away, likely explaining the observed lack of contribution of the CBMs to activity Daha fazlası Daha az

Kapsiotis, Argyrios | Rassios, Anne Ewing | Uysal, Ibrahim | Grieco, Giovanni | Akmaz, Recep Melih | Saka, Samet | Bussolesi, Micol

Article | 2018 | JOURNAL OF GEOCHEMICAL EXPLORATION185 , pp.14 - 32

The chrome ores of the retired Metalleion mine of the Othris ophiolite are hosted in a small volume of a pervasively serpentinized, tabular harzburgite body. These ores have been studied to determine their geological mode of occurrence, mineralogy and chromian spinel (Cr-spinel) chemistry. The ores consist of massive chromitite (85-95% modal Cr-spinel) with mylonitic fabric in imbricate-shaped pods. Chromian spinel displays a limited range in Cr# [Cr/(Cr + Al) x 100 = 53-63] and Mg# [Mg/(Mg + Fe2+) x 100 = 59-73] and low TiO2 content (