RqcH and RqcP catalyze processive poly-alanine synthesis in a reconstituted ribosome-associated quality control system

In the cell, stalled ribosomes are rescued through ribosome-associated protein quality-control (RQC) pathways. After splitting of the stalled ribosome, a C-terminal polyalanine ‘tail’ is added to the unfinished polypeptide attached to the tRNA on the 50S ribosomal subunit. In Bacillus subtilis, polyalanine tailing is catalyzed by the NEMF family protein RqcH, in cooperation with RqcP. However, the mechanistic details of this process remain unclear. Here we demonstrate that RqcH is responsible for tRNA^Ala selection during RQC elongation, whereas RqcP lacks any tRNA specificity. The ribosomal protein uL11 is crucial for RqcH, but not RqcP, recruitment to the 50S subunit, and B. subtilis lacking uL11 are RQC-deficient. Through mutational mapping, we identify critical residues within RqcH and RqcP that are important for interaction with the P-site tRNA and/or the 50S subunit. Additionally, we have reconstituted polyalanine-tailing in vitro and can demonstrate that RqcH and RqcP are necessary and sufficient for processivity in a minimal system. Moreover, the in vitro reconstituted system recapitulates our in vivo findings by reproducing the importance of conserved residues of RqcH and RqcP for functionality. Collectively, our findings provide mechanistic insight into the role of RqcH and RqcP in the bacterial RQC pathway.     

The Comparative Analysis of Carboxylic Acid Composition of Four Iris Species from Ukraine

The present article reports results of analysis of carboxylic acids in leaves of Iris species from Ukraine using a gas chromatography (GC) method with mass spectrometric (MS) detection (GC/MS). Carboxylic acids play significant roles in contemporary society as evidenced by multiple applications in fields of medicine, agriculture, pharmacy, food, and other industries. Study of natural plant products as a source of organic acids is of particular interest. Carboxylic acid composition of leaves of Iris hungarica Waldst. & Kit., Iris germanica L., Iris pallida Lam., and Iris variegate L. was studied for the first time applying GC/MS method. The mass spectrums of compounds were matched with NIST and WILEY Libraries. The GC/MS analysis revealed the presence of 26 common acids in the plant raw materials studied. The short-chain carboxylic acids, such as citric (1337.5–12364.4 mg/kg), malic (50.8–4558.0 mg/kg) and oxalic (1199.0–3435.2 mg/kg) acids were contained in significantly high quantity in all samples. Ferulic, p-coumaric and vanillic acids were the most abundant among phenolic acids. α-Linolenic acid was dominant in the leaves of I. germanica (869.5 mg/kg), I. pallida (753.3 mg/kg), and I. variegate (250.3 mg/kg) among polyunsaturated fatty acids, however, linoleic acid prevailed in the plant raw material of I. hungarica (1150.7 mg/kg). Since the leaves of Iris species studied contain carboxylic acids with diverse pharmacological activity, extracts of these raw materials are perspective for development food supplements and medicines.     

Phytochemical Analysis and Antioxidant Activity of <i>Crocus speciosus</i> Leaves

The numerous studies indicate leaves of plants are a rich source of bioactive compounds that can be a valuable source of compounds used in the pharmaceutical and cosmetic industries. Aim of this study was to investigate the chemical composition and the antioxidant property of Crocus speciosus leaves. Primary phytochemical screening of C. speciosus leaves revealed the presence of some following compound categories such as phenolic compounds, aminoacids, saponins, proteins, tannins, triterpenoids, glycosides, polysaccharides. The total flavonoids and phenolic compounds content were determined spectrophotometrically and by HPLC-DAD and HPLC-MS. Antiradical activity was determined by ABTS radical-cation scavenging method, spectrophotometrically. The total amount of flavonoids in C. speciosus leaves was 1.07 ± 0.02 mg RE/g (p < 0.05), the total amount of phenolic compounds was 0.41 ± 0.01 mg GAE/g (p < 0.05). By HPLC-DAD-MS analysis the presence of the mangiferin, chlorogenic acid, isoorientin, kaempferol, hyperoside, and isoquercitin was established for the first time in Crocus leaves. The antiradical activity of C. speciosus leaves extracts was 150.08 ± 4.5 μmol/g (p < 0.05) and its was mainly attributed to phenolic compounds content. The high amounts of flavonoids and antiradical activity in C. speciosus leaves suggests promising phytochemical and pharmacological study of this Crocus species.