Structural and Biochemical Characterization of Mycobacterium tuberculosis Zinc SufU-SufS Complex.

Iron-sulfur (Fe-S) clusters are inorganic prosthetic groups in proteins composed exclusively of iron and inorganic sulfide. These cofactors are required in a wide range of critical cellular pathways. Iron-sulfur clusters do not form spontaneously in vivo; several proteins are required to mobilize sulfur and iron, assemble and traffic-nascent clusters. Bacteria have developed several Fe-S assembly systems, such as the ISC, NIF, and SUF systems. Interestingly, in Mycobacterium tuberculosis (Mtb), the causative agent of tuberculosis (TB), the SUF machinery is the primary Fe-S biogenesis system. This operon is essential for the viability of Mtb under normal growth conditions, and the genes it contains are known to be vulnerable, revealing the Mtb SUF system as an interesting target in the fight against tuberculosis. In the present study, two proteins of the Mtb SUF system were characterized for the first time: Rv1464(sufS) and Rv1465(sufU). The results presented reveal how these two proteins work together and thus provide insights into Fe-S biogenesis/metabolism by this pathogen. Combining biochemistry and structural approaches, we showed that Rv1464 is a type II cysteine-desulfurase enzyme and that Rv1465 is a zinc-dependent protein interacting with Rv1464. Endowed with a sulfurtransferase activity, Rv1465 significantly enhances the cysteine-desulfurase activity of Rv1464 by transferring the sulfur atom from persulfide on Rv1464 to its conserved Cys40 residue. The zinc ion is important for the sulfur transfer reaction between SufS and SufU, and His354 in SufS plays an essential role in this reaction. Finally, we showed that Mtb SufS-SufU is more resistant to oxidative stress than E. coli SufS-SufE and that the presence of zinc in SufU is likely responsible for this improved resistance. This study on Rv1464 and Rv1465 will help guide the design of future anti-tuberculosis agents.

Membrane-Bound Flavocytochrome MsrQ Is a Substrate of the Flavin Reductase Fre in Escherichia coli.

MsrPQ is a new type of methionine sulfoxide reductase (Msr) system found in bacteria. It is specifically involved in the repair of periplasmic methionine residues that are oxidized by hypochlorous acid. MsrP is a periplasmic molybdoenzyme that carries out the Msr activity, whereas MsrQ, an integral membrane-bound hemoprotein, acts as the physiological partner of MsrP to provide electrons for catalysis. Although MsrQ (YedZ) was associated since long with a protein superfamily named FRD (ferric reductase domain), including the eukaryotic NADPH oxidases and STEAP proteins, its biochemical properties are still sparsely documented. Here, we have investigated the cofactor content of the E. coli MsrQ and its mechanism of reduction by the flavin reductase Fre. We showed by electron paramagnetic resonance (EPR) spectroscopy that MsrQ contains a single highly anisotropic low-spin (HALS) b-type heme located on the periplasmic side of the membrane. We further demonstrated that MsrQ holds a flavin mononucleotide (FMN) cofactor that occupies the site where a second heme binds in other members of the FDR superfamily on the cytosolic side of the membrane. EPR spectroscopy indicates that the FMN cofactor can accommodate a radical semiquinone species. The cytosolic flavin reductase Fre was previously shown to reduce the MsrQ heme. Here, we demonstrated that Fre uses the FMN MsrQ cofactor as a substrate to catalyze the electron transfer from cytosolic NADH to the heme. Formation of a specific complex between MsrQ and Fre could favor this unprecedented mechanism, which most likely involves transfer of the reduced FMN cofactor from the Fre active site to MsrQ.

[A multidisciplinary approach to cardiac rehabilitation]. / La réadaptation cardiaque, un accompagnement pluriprofessionnel.

The rehabilitation of a coronary patient involves numerous professionals in a global care approach. The objective is to reintroduce physical activity and put in place lifestyle changes, in order to reduce the risk factors. Therapeutic education is an essential part of this support.

Minor biflavonoids from Lophira alata leaves.

The leaves of the Cameroonian medicinal plant Lophira alata afforded two new biflavonoids, lophirone L (1) and lophirone M (2), and the known luteolin and lithospermoside. Both biflavonoids were obtained in small quantities, and their structures show some new and unusual biflavonoid diversity.