In Silico Identification of a Key Residue for Substrate Recognition of the Riboflavin Membrane Transporter RFVT3.

Because of its specific physicochemical properties (fluorescence, photosensitizing, and redox reactions), vitamin B2, also called riboflavin (RF), has been generating a lot of interest in the fields of nanotechnology and bioengineering in the last decade. RF, by targeting its riboflavin transporters (RFVTs) overexpressed in some cancers, is particularly used to functionalize nanovectors for anticancer drug delivery. From a physiopathological point of view, an RF deficiency has been implicated in various pathologies, including mendelian diseases. RF deficiency is mainly due to natural variants of its RFVTs that make them inactive and therefore prevent RF transport. The lack of structural data about RFVT is a major drawback for a better understanding of the role of the mutations in the molecular mechanism of these transporters. In this context, this work was aimed at investigating the 3D structure of RFVT3 and its interactions with RF. For this purpose, we used an in silico procedure including protein threading, docking, and molecular dynamics. Our results propose that the natural variant W17R, known to be responsible for the Brown-Vialetto-Van Laere syndrome, prevents the recognition of RF by RFVT3 and thus blocks its transport. This in silico procedure could be used for elucidating the impact of pathogenic mutations of other proteins. Moreover, the identification of RF binding sites will be useful for the design of RF-functionalized nanovectors.

Modelling central metabolic fluxes by constraint-based optimization reveals metabolic reprogramming of developing Solanum lycopersicum (tomato) fruit.

Modelling of metabolic networks is a powerful tool to analyse the behaviour of developing plant organs, including fruits. Guided by our current understanding of heterotrophic metabolism of plant cells, a medium-scale stoichiometric model, including the balance of co-factors and energy, was constructed in order to describe metabolic shifts that occur through the nine sequential stages of Solanum lycopersicum (tomato) fruit development. The measured concentrations of the main biomass components and the accumulated metabolites in the pericarp, determined at each stage, were fitted in order to calculate, by derivation, the corresponding external fluxes. They were used as constraints to solve the model by minimizing the internal fluxes. The distribution of the calculated fluxes of central metabolism were then analysed and compared with known metabolic behaviours. For instance, the partition of the main metabolic pathways (glycolysis, pentose phosphate pathway, etc.) was relevant throughout fruit development. We also predicted a valid import of carbon and nitrogen by the fruit, as well as a consistent CO2 release. Interestingly, the energetic balance indicates that excess ATP is dissipated just before the onset of ripening, supporting the concept of the climacteric crisis. Finally, the apparent contradiction between calculated fluxes with low values compared with measured enzyme capacities suggest a complex reprogramming of the metabolic machinery during fruit development. With a powerful set of experimental data and an accurate definition of the metabolic system, this work provides important insight into the metabolic and physiological requirements of the developing tomato fruits.

Comparative study of strong cation exchangers: Structure-related chromatographic performances.

Chromatographic performances are highly influenced by operational parameters. New ion exchangers have tailored matrices providing low backpressure, thereby allowing high flow velocity. By systematic frontal analysis and selectivity determination at different flow rates, we independently evaluated cation exchangers to facilitate media selection and investigated the relationship between surface modification and chromatographic performances. Structure-extended resins showed higher binding capacities compared to resins with conventional ligands directly attached to the matrix. Moreover, they maintained high capacities even with high flow velocities. Ligand accessibility was therefore largely enhanced, allowing proteins to interact and bind under harsh conditions with minimal residence/contact time. High throughput resins can be used for purification of high volume and high concentration feedstock in limited time. This results in higher productivity, and could contribute to cost reduction. In this work, we evaluated the dynamic binding capacities of various new ion exchange resins at different binding conductivities for different residence times, and observed that.