Substrate specificity of a peptidyl-aminoacyl-l/d-isomerase from frog skin

In the skin of fire-bellied toads (Bombina species), an aminoacyl-l/d-isomerase activity is present which catalyses the post-translational isomerization of the l- to the d-form of the second residue of its substrate peptides. Previously, this new type of enzyme was studied in some detail and genes potentially coding for similar polypeptides were found to exist in several vertebrate species including man. Here, we present our studies to the substrate specificity of this isomerase using fluorescence-labeled variants of the natural substrate bombinin H with different amino acids at positions 1, 2 or 3. Surprisingly, this enzyme has a rather low selectivity for residues at position 2 where the change of chirality at the alpha-carbon takes place. In contrast, a hydrophobic amino acid at position 1 and a small one at position 3 of the substrate are essential. Interestingly, some peptides containing a Phe at position 3 also were substrates. Furthermore, we investigated the role of the amino-terminus for substrate recognition. In view of the rather broad specificity of the frog isomerase, we made a databank search for potential substrates of such an enzyme. Indeed, numerous peptides of amphibia and mammals were found which fulfill the requirements determined in this study. Expression of isomerases with similar characteristics in other species can therefore be expected to catalyze the formation of peptides containing d-amino acids

Proteolysis-Dependent Remodeling of the Tubulin Homolog FtsZ at the Division Septum in \u3ci\u3eEscherichia coli\u3c/i\u3e

During bacterial cell division a dynamic protein structure called the Z-ring assembles at the septum. The major protein in the Z-ring in Escherichia coli is FtsZ, a tubulin homolog that polymerizes with GTP. FtsZ is degraded by the two-component ATP-dependent protease ClpXP. Two regions of FtsZ, located outside of the polymerization domain in the unstructured linker and at the C-terminus, are important for specific recognition and degradation by ClpXP. We engineered a synthetic substrate containing green fluorescent protein (Gfp) fused to an extended FtsZ C-terminal tail (residues 317–383), including the unstructured linker and the C-terminal conserved region, but not the polymerization domain, and showed that it is sufficient to target a non-native substrate for degradation in vitro. To determine if FtsZ degradation regulates Z-ring assembly during division, we expressed a full length Gfp-FtsZ fusion protein in wild type and clp deficient strains and monitored fluorescent Z-rings. In cells deleted for clpX or clpP, or cells expressing protease-defective mutant protein ClpP(S97A), Z-rings appear normal; however, after photobleaching a region of the Z-ring, fluorescence recovers ~70% more slowly in cells without functional ClpXP than in wild type cells. Gfp-FtsZ(R379E), which is defective for degradation by ClpXP, also assembles into Z-rings that recover fluorescence ~2-fold more slowly than Z-rings containing Gfp-FtsZ. In vitro, ClpXP cooperatively degrades and disassembles FtsZ polymers. These results demonstrate that ClpXP is a regulator of Z-ring dynamics and that the regulation is proteolysis-dependent. Our results further show that FtsZ-interacting proteins in E. coli fine-tune Z-ring dynamics

Lawson criterion for ignition exceeded in an inertial fusion experiment

For more than half a century, researchers around the world have been engaged in attempts to achieve fusion ignition as a proof of principle of various fusion concepts. Following the Lawson criterion, an ignited plasma is one where the fusion heating power is high enough to overcome all the physical processes that cool the fusion plasma, creating a positive thermodynamic feedback loop with rapidly increasing temperature. In inertially confined fusion, ignition is a state where the fusion plasma can begin "burn propagation" into surrounding cold fuel, enabling the possibility of high energy gain. While "scientific breakeven" (i.e., unity target gain) has not yet been achieved (here target gain is 0.72, 1.37 MJ of fusion for 1.92 MJ of laser energy), this Letter reports the first controlled fusion experiment, using laser indirect drive, on the National Ignition Facility to produce capsule gain (here 5.8) and reach ignition by nine different formulations of the Lawson criterion

Electronic Cigarette Awareness, Use, and Perceptions among Cancer Patients

Objective Electronic cigarettes (e-cigs) are an emerging trend, yet little is known about their use in the cancer population. The objectives of this study were (1) to describe characteristics of e-cig use among cancer patients, (2) to define e-cig advertising exposure, and (3) to characterize perceptions of traditional cigarettes versus e-cigs. Study Design Cross-sectional study. Setting Comprehensive cancer center. Subjects and Methods Inpatient, current smokers with a cancer diagnosis. E-cig exposure and use were defined using descriptive statistics. Wilcoxon rank test was used to compare perceptions between e-cigs and traditional cigarettes. Results A total of 979 patients were enrolled in the study; 39 cancer patients were identified. Most cancer patients were women (59%), with an average age of 53.3 years. Of the patients, 46.2% reported e-cig use, most of which (88.9%) was “experimental or occasional.” The primary reason for e-cig use was to aid smoking cessation (66.7%), alternative use in nonsmoking areas (22.2%), and “less risky” cigarette replacement (5.6%). The most common sources for e-cig information were TV (76.9%), stores (48.7%), friends (35.9%), family (30.8%), and newspapers or magazines (12.8%). Compared with cigarettes, e-cigs were viewed as posing a reduced health risk ( P < .001) and conferring a less negative social impression ( P < .001). They were also viewed as less likely to satisfy nicotine cravings ( P = .002), to relieve boredom ( P = .0005), to have a calming effect ( P < .001), and as tasting pleasant ( P = .006) Conclusions E-cig use and advertising exposure are common among cancer patients. E-cig use is perceived as healthier and more socially acceptable but less likely to produce a number of desired consequences of cigarette use