Physiologically relevant reconstitution of iron-sulfur cluster biosynthesis uncovers persulfide-processing functions of ferredoxin-2 and frataxin.

Iron-sulfur (Fe-S) clusters are essential protein cofactors whose biosynthetic defects lead to severe diseases among which is Friedreich's ataxia caused by impaired expression of frataxin (FXN). Fe-S clusters are biosynthesized on the scaffold protein ISCU, with cysteine desulfurase NFS1 providing sulfur as persulfide and ferredoxin FDX2 supplying electrons, in a process stimulated by FXN but not clearly understood. Here, we report the breakdown of this process, made possible by removing a zinc ion in ISCU that hinders iron insertion and promotes non-physiological Fe-S cluster synthesis from free sulfide in vitro. By binding zinc-free ISCU, iron drives persulfide uptake from NFS1 and allows persulfide reduction into sulfide by FDX2, thereby coordinating sulfide production with its availability to generate Fe-S clusters. FXN stimulates the whole process by accelerating persulfide transfer. We propose that this reconstitution recapitulates physiological conditions which provides a model for Fe-S cluster biosynthesis, clarifies the roles of FDX2 and FXN and may help develop Friedreich's ataxia therapies.

Comparative Study of Oil Quality and Aroma Profiles from Tunisian Olive Cultivars Growing in Saharian Oasis Using Chemometric Analysis.

Aroma profile, oxidative stability and quality parameters of virgin olive oil from four cultivars (Chemlali, Chetoui, Koroneiki and Rjim), grown in Rjim Maatoug oasis in southern of Tunisia, were studied for the first time. The olive oil samples were obtained during maturation from a crop season (2012-2013). The results showed the quality parameters, i.e., free fatty acid, UV absorbance at 232 and 270 nm, increases during maturation exceeding the upper limit established by the IOOC norm. Chlorophyll and carotenoid pigments tended to decrease during ripening stages. The trend of oxidative stability, total phenols and Odiphenols exhibited a reduction of antioxidant activity at more advanced stages of maturity. The marks achieved showed that oil quality degradation is due to the great drought of climate: high temperature, high light intensity and low rainfall. Studied aroma profiles of cultivars were also influenced by severe climatic conditions. Twenty-four compounds were characterized, representing 94.8-99.8% of the total volatiles. In all samples, a strong decrease was observed in aldehydes compounds.

Effect of agricultural sites on differentiation between Chemlali and Neb Jmel olive oils.

The chemical composition, oxidative stability, aroma and sensory profiles of virgin olive oils from two Tunisian cultivars, Chemlali and Neb Jmel, grown in two different locations, the center and south of Tunisia, have been evaluated. There were significant differences between the oils from both cultivars when grown in the two different environments. At higher altitude, the oils showed a greater amount of oleic acid, phenols and a higher oxidative stability, while at lower altitude, the oils had higher saturated and linoleic acid contents. The aroma profiles in Chemlali and Neb Jmel cultivars were also influenced by the pedoclimatic conditions, as shown by the difference in volatiles as a function of the geographical area. The volatile compounds of the monovarietal virgin olive oils were identified and compared using headspace solid-phase microextraction (HS-SPME) technique coupled with GC-MS and GC-FID. The proportions of different classes of volatiles of the oils have shown significant differences throughout the obtained oils. These results suggest that besides the genetic factor, the agronomic conditions affect the volatile formation and, therefore, the organoleptic properties of VOO, and can be used to discriminate and characterize the Chemlali and Neb Jmel olive oils from each region.