The Role of CyaY in Iron Sulfur Cluster Assembly on the E. coli IscU Scaffold Protein

Progress in understanding the mechanism underlying the enzymatic formation of iron-sulfur clusters is difficult since it involves a complex reaction and a multi-component system. By exploiting different spectroscopies, we characterize the effect on the enzymatic kinetics of cluster formation of CyaY, the bacterial ortholog of frataxin, on cluster formation on the scaffold protein IscU. Frataxin/CyaY is a highly conserved protein implicated in an incurable ataxia in humans. Previous studies had suggested a role of CyaY as an inhibitor of iron sulfur cluster formation. Similar studies on the eukaryotic proteins have however suggested for frataxin a role as an activator. Our studies independently confirm that CyaY slows down the reaction and shed new light onto the mechanism by which CyaY works. We observe that the presence of CyaY does not alter the relative ratio between [2Fe2S]2+ and [4Fe4S]2+ but directly affects enzymatic activity

Canagliflozin and Cardiovascular and Renal Outcomes in Type 2 Diabetes Mellitus and Chronic Kidney Disease in Primary and Secondary Cardiovascular Prevention Groups

Background: Canagliflozin reduces the risk of kidney failure in patients with type 2 diabetes mellitus and chronic kidney disease, but effects on specific cardiovascular outcomes are uncertain, as are effects in people without previous cardiovascular disease (primary prevention). Methods: In CREDENCE (Canagliflozin and Renal Events in Diabetes With Established Nephropathy Clinical Evaluation), 4401 participants with type 2 diabetes mellitus and chronic kidney disease were randomly assigned to canagliflozin or placebo on a background of optimized standard of care. Results: Primary prevention participants (n=2181, 49.6%) were younger (61 versus 65 years), were more often female (37% versus 31%), and had shorter duration of diabetes mellitus (15 years versus 16 years) compared with secondary prevention participants (n=2220, 50.4%). Canagliflozin reduced the risk of major cardiovascular events overall (hazard ratio [HR], 0.80 [95% CI, 0.67-0.95]; P=0.01), with consistent reductions in both the primary (HR, 0.68 [95% CI, 0.49-0.94]) and secondary (HR, 0.85 [95% CI, 0.69-1.06]) prevention groups (P for interaction=0.25). Effects were also similar for the components of the composite including cardiovascular death (HR, 0.78 [95% CI, 0.61-1.00]), nonfatal myocardial infarction (HR, 0.81 [95% CI, 0.59-1.10]), and nonfatal stroke (HR, 0.80 [95% CI, 0.56-1.15]). The risk of the primary composite renal outcome and the composite of cardiovascular death or hospitalization for heart failure were also consistently reduced in both the primary and secondary prevention groups (P for interaction >0.5 for each outcome). Conclusions: Canagliflozin significantly reduced major cardiovascular events and kidney failure in patients with type 2 diabetes mellitus and chronic kidney disease, including in participants who did not have previous cardiovascular disease

Canagliflozin and renal outcomes in type 2 diabetes and nephropathy

BACKGROUND Type 2 diabetes mellitus is the leading cause of kidney failure worldwide, but few effective long-term treatments are available. In cardiovascular trials of inhibitors of sodium–glucose cotransporter 2 (SGLT2), exploratory results have suggested that such drugs may improve renal outcomes in patients with type 2 diabetes. METHODS In this double-blind, randomized trial, we assigned patients with type 2 diabetes and albuminuric chronic kidney disease to receive canagliflozin, an oral SGLT2 inhibitor, at a dose of 100 mg daily or placebo. All the patients had an estimated glomerular filtration rate (GFR) of 30 to <90 ml per minute per 1.73 m2 of body-surface area and albuminuria (ratio of albumin [mg] to creatinine [g], >300 to 5000) and were treated with renin–angiotensin system blockade. The primary outcome was a composite of end-stage kidney disease (dialysis, transplantation, or a sustained estimated GFR of <15 ml per minute per 1.73 m2), a doubling of the serum creatinine level, or death from renal or cardiovascular causes. Prespecified secondary outcomes were tested hierarchically. RESULTS The trial was stopped early after a planned interim analysis on the recommendation of the data and safety monitoring committee. At that time, 4401 patients had undergone randomization, with a median follow-up of 2.62 years. The relative risk of the primary outcome was 30% lower in the canagliflozin group than in the placebo group, with event rates of 43.2 and 61.2 per 1000 patient-years, respectively (hazard ratio, 0.70; 95% confidence interval [CI], 0.59 to 0.82; P=0.00001). The relative risk of the renal-specific composite of end-stage kidney disease, a doubling of the creatinine level, or death from renal causes was lower by 34% (hazard ratio, 0.66; 95% CI, 0.53 to 0.81; P<0.001), and the relative risk of end-stage kidney disease was lower by 32% (hazard ratio, 0.68; 95% CI, 0.54 to 0.86; P=0.002). The canagliflozin group also had a lower risk of cardiovascular death, myocardial infarction, or stroke (hazard ratio, 0.80; 95% CI, 0.67 to 0.95; P=0.01) and hospitalization for heart failure (hazard ratio, 0.61; 95% CI, 0.47 to 0.80; P<0.001). There were no significant differences in rates of amputation or fracture. CONCLUSIONS In patients with type 2 diabetes and kidney disease, the risk of kidney failure and cardiovascular events was lower in the canagliflozin group than in the placebo group at a median follow-up of 2.62 years

Mössbauer spectroscopy.

International audienceGiven its ability to detect all iron centers, to identify their electronic structures, and to quantify the ratios of the different iron forms present in a sample, many researchers turn to Mössbauer spectroscopy when wanting to address structural and mechanistic questions involving iron proteins. Yet, this technique applied to biochemistry is provided by only a few dedicated teams in the world. Technical difficulties ranging from sample preparation to data analysis and interpretation make necessary the collaboration between biochemists and Mössbauer spectroscopists. This chapter will be confined to iron Mössbauer. It will focus on giving biologists and biochemists the keys to understand what essential information Mössbauer spectroscopy can yield, and how to engage in successful collaborations with spectroscopists. After introducing the basic principles of a Mössbauer experiment, we will describe first how to prepare a suitable Mössbauer sample, then how this technique is applied to the identification of different iron species inside proteins

Contribution of Mössbauer spectroscopy to the investigation of Fe/S biogenesis.

International audienceFe/S cluster biogenesis involves a complex machinery comprising several mitochondrial and cytosolic proteins. Fe/S cluster biosynthesis is closely intertwined with iron trafficking in the cell. Defects in Fe/S cluster elaboration result in severe diseases such as Friedreich ataxia. Deciphering this machinery is a challenge for the scientific community. Because iron is a key player, $^{57}$Fe-Mössbauer spectroscopy is especially appropriate for the characterization of Fe species and monitoring the iron distribution. This minireview intends to illustrate how Mössbauer spectroscopy contributes to unravel steps in Fe/S cluster biogenesis. Studies were performed on isolated proteins that may be present in multiple protein complexes. Since a few decades, Mössbauer spectroscopy was also performed on whole cells or on isolated compartments such as mitochondria and vacuoles, affording an overview of the iron trafficking

A three-coordinate Fe(ii) center within a [3Fe-(μ3-S)] cluster that provides an accessible coordination site.

International audienceA μ3-sulfide bridged triiron cluster(ii,ii,iii) supported by a cyclophane ligand undergoes metal-based reduction to yield an all-ferrous species. The latter complex incorporates a three-coordinate iron center that provides an accessible coordination site to a solvent molecule