Conformational tuning improves the stability of spirocyclic nitroxides with long paramagnetic relaxation times.

Nitroxides are widely used as probes and polarization transfer agents in spectroscopy and imaging. These applications require high stability towards reducing biological environments, as well as beneficial relaxation properties. While the latter is provided by spirocyclic groups on the nitroxide scaffold, such systems are not in themselves robust under reducing conditions. In this work, we introduce a strategy for stability enhancement through conformational tuning, where incorporating additional substituents on the nitroxide ring effects a shift towards highly stable closed spirocyclic conformations, as indicated by X-ray crystallography and density functional theory (DFT) calculations. Closed spirocyclohexyl nitroxides exhibit dramatically improved stability towards reduction by ascorbate, while maintaining long relaxation times in electron paramagnetic resonance (EPR) spectroscopy. These findings have important implications for the future design of new nitroxide-based spin labels and imaging agents.

The Myxobacterial Antibiotic Myxovalargin: Biosynthesis, Structural Revision, Total Synthesis, and Molecular Characterization of Ribosomal Inhibition.

Resistance of bacterial pathogens against antibiotics is declared by WHO as a major global health threat. As novel antibacterial agents are urgently needed, we re-assessed the broad-spectrum myxobacterial antibiotic myxovalargin and found it to be extremely potent against Mycobacterium tuberculosis. To ensure compound supply for further development, we studied myxovalargin biosynthesis in detail enabling production via fermentation of a native producer. Feeding experiments as well as functional genomics analysis suggested a structural revision, which was eventually corroborated by the development of a concise total synthesis. The ribosome was identified as the molecular target based on resistant mutant sequencing, and a cryo-EM structure revealed that myxovalargin binds within and completely occludes the exit tunnel, consistent with a mode of action to arrest translation during a late stage of translation initiation. These studies open avenues for structure-based scaffold improvement toward development as an antibacterial agent.

Vps37a regulates hepatic glucose production by controlling glucagon receptor localization to endosomes.

During mammalian energy homeostasis, the glucagon receptor (Gcgr) plays a key role in regulating both glucose and lipid metabolisms. However, the mechanisms by which these distinct signaling arms are differentially regulated remain poorly understood. Using a Cy5-glucagon agonist, we show that the endosomal protein Vps37a uncouples glucose production from lipid usage downstream of Gcgr signaling by altering intracellular receptor localization. Hepatocyte-specific knockdown of Vps37a causes an accumulation of Gcgr in endosomes, resulting in overactivation of the cAMP/PKA/p-Creb signaling pathway to gluconeogenesis without affecting ß-oxidation. Shifting the receptor back to the plasma membrane rescues the differential signaling and highlights the importance of the spatiotemporal localization of Gcgr for its metabolic effects. Importantly, since Vps37a knockdown in animals fed with a high-fat diet leads to hyperglycemia, although its overexpression reduces blood glucose levels, these data reveal a contribution of endosomal signaling to metabolic diseases that could be exploited for treatments of type 2 diabetes.

Prolongation of the QTc interval in HIV-infected individuals compared to the general population.

OBJECTIVES: Prolonged QT interval is associated with arrhythmias and sudden death. An increased prevalence of QT interval prolongation in human immunodeficiency virus-infected (HIV) subjects was previously described. The impact of different medications and HIV infection itself on the QT interval is rarely investigated in large HIV+ cohorts. METHODS: We compared QT interval measurement in 496 HIV(+) patients of the HIV-HEART study (HIVH) and 992 sex- and age-matched controls of the population-based German Heinz Nixdorf Recall study (HNR). QT corrected for heart rate (QTc) >440 ms in male and >460 ms in female was considered pathological. We analysed the impact of HIV status and HIV medication on QTc prolongation in the HIVH subjects. RESULTS: We observed longer QTc in HIVH subjects compared with HNR controls: 424.1 ms ± 23.3 vs. 411.3 ± 15.3 ms for male and 435.5 ms ± 19.6 vs. 416.4 ms ± 17.3 for female subjects (p < 0.0001 for both sexes). Adjusting for QT prolonging medication the mean differences in QTc between the two studies remained significant with 12.6 ms (95% CI 10.5-14.8; p value <0.0001) for male and 19.3 ms (95% CI 14.5-24.2; p value <0.0001) for female subjects. Prolongation of QTc was pathologic in 22.8 vs. 3.9% of HIV(+) and non-infected males and in 12.1 vs. 1.8% of the females [OR of 7.9 (5.0-12.6) and OR of 6.7 (1.8-24.2), respectively]. Smoking behaviour was an independent factor to lengthen QTc in HIV(+) patients. Diabetes mellitus was not a risk factor itself, but might be associated with medication which was associated with LQT. We could not observe any influence of the HIV status, ART, or any co-medication on the QTc. CONCLUSIONS: Our study showed that HIV(+) patients had significantly longer QTc intervals compared to the general population. The number of patients with pathologic QTc prolongation was significantly increased in HIV(+) population.

Characterisation of the Broadly-Specific O-Methyl-transferase JerF from the Late Stages of Jerangolid Biosynthesis.

We describe the characterisation of the O-methyltransferase JerF from the late stages of jerangolid biosynthesis. JerF is the first known example of an enzyme that catalyses the formation of a non-aromatic, cyclic methylenolether. The enzyme was overexpressed in E. coli and the cell-free extracts were used in bioconversion experiments. Chemical synthesis gave access to a series of substrate surrogates that covered a broad structural space. Enzymatic assays revealed a broad substrate tolerance and high regioselectivity of JerF, which makes it an attractive candidate for an application in chemoenzymatic synthesis with particular usefulness for late stage application on 4-methoxy-5,6-dihydro-2H-pyran-2-one-containing natural products.