Edited by Ruma BanerjeeGlutathione degradation plays an important role in glutathione and redox homeostasis, and thus it is imperative to understand the enzymes and the mechanisms involved in glutathione degradation in detail. We describe here ChaC2, a member of the ChaC family of ␥-glutamylcyclotransferases, as an enzyme that degrades glutathione in the cytosol of mammalian cells. ChaC2 is distinct from the previously described ChaC1, to which ChaC2 shows ϳ50% sequence identity. and ChaC2 proteins also shared the same specificity for reduced glutathione, with no activity against either ␥-glutamyl amino acids or oxidized glutathione. The ChaC2 proteins were found to be expressed constitutively in cells, unlike the tightly regulated ChaC1. Moreover, lower eukaryotes have a single member of the ChaC family that appears to be orthologous to ChaC2. In addition, we determined the crystal structure of yeast ChaC2 homologue, GCG1, at 1.34 Å resolution, which represents the first structure of the ChaC family of proteins. The catalytic site is defined by a fortuitous benzoic acid molecule bound to the crystal structure. The mechanism for binding and catalytic activity of this new enzyme of glutathione degradation, which is involved in continuous but basal turnover of cytosolic glutathione, is proposed.

Glutathione depletion leads to calcium influx in yeast cells via plasma membrane Cch1p and the vacuolar Yvc1p channels. Yvc1p, a yeast vacuolar transient receptor potential channel, is activated by glutathionylation carried out by the glutathione S-transferase Gtt1p, and this mechanism is reversible with deglutathionylation being mediated by the thioredoxin Trx2p.

Receptors for bitter, sugar, and other tastes have been identified in the fruit fly Drosophila melanogaster, while a broadly tuned receptor for the taste of acid has been elusive. Previous work showed that such a receptor was unlikely to be encoded by a gene within one of the two major families of taste receptors in Drosophila, the “gustatory receptors” and “ionotropic receptors.” Here, to identify the acid taste receptor, we tested the contributions of genes encoding proteins distantly related to the mammalian Otopertrin1 (OTOP1) proton channel that functions as a sour receptor in mice. RNA interference (RNAi) knockdown or mutation by CRISPR/Cas9 of one of the genes, Otopetrin-Like A (OtopLA), but not of the others (OtopLB or OtopLC) severely impaired the behavioral rejection to a sweet solution laced with high levels of HCl or carboxylic acids and greatly reduced acid-induced action potentials measured from taste hairs. An isoform of OtopLA that we isolated from the proboscis was sufficient to restore behavioral sensitivity and acid-induced action potential firing in OtopLA mutant flies. At lower concentrations, HCl was attractive to the flies, and this attraction was abolished in the OtopLA mutant. Cell type–specific rescue experiments showed that OtopLA functions in distinct subsets of gustatory receptor neurons for repulsion and attraction to high and low levels of protons, respectively. This work highlights a functional conservation of a sensory receptor in flies and mammals and shows that the same receptor can function in both appetitive and repulsive behaviors.

Many of the Drosophila receptors required for bitter, sugar and other tastes have been identified. However, the receptor required for the taste of acid has been elusive. In Drosophila, the major families of taste receptors, such as Gustatory Receptors and Ionotropic Receptors are unrelated to taste receptors in mammals. Previous work indicated that members of these major families do not appear to be broadly required acid sensors. Here, to identify the enigmatic acid taste receptor, we interrogated three genes encoding proteins distantly related the mammalian Otopertrin1 proton channel. We found that RNAi knockdown or mutation of Otopetrin-Like A (OtopLA) by CRISPR/Cas9, severely impairs the behavioral rejection of sugary foods laced with HCl or carboxylic acids. Mutation of OtopLA also greatly reduces acid-induced action potentials. We identified an isoform of OtopLA that was expressed in the proboscis and was sufficient to restore acid sensitivity to OtopLA mutant flies. OtopLA functioned in acid taste in a subset of bitter-activated gustatory receptor neurons that senses protons. This work highlights an unusual functional conservation of a receptor required for a taste modality in flies and mammals.

Promoter hypermethylation plays an important role in the inactivation of tumor suppressor/metabolic genes during tumorigenesis. The screening of high-risk population (smokers) for hypermethylation pattern in tumor suppressor/metabolic genes can be a good noninvasive biomarker tool, which should be included in prognosis so that therapeutic measures can be initiated at an early stage. The purpose of this study was to determine the prevalence of aberrant promoter methylation of GSTP1, p16, p14, and RASSF1A genes in smokers and nonsmokers of North India. Our study showed that compared with nonsmokers, smokers have an increased risk of hypermethylation in these genes. We found that 57.3% of the smokers samples showed methylation for GSTP1, 38% for p16, 18% for p14, and 32% for RASSF1A. Our population study allowed us to reveal the relationship between smoking and the subsequent appearance of an epigenetic change. Smoking speeds up the hypermethylation of these genes, which are thus unable to express, making the person more susceptible to the risk of lung and other solid carcinomas. Hypermethylation studies on DNA from two lung cancer cell lines (A549 and H460) were also done to compare the results, and the results are similar to samples of smokers.