Cotranslational folding of proteins on the ribosome.

Many proteins in the cell fold cotranslationally within the restricted space of the polypeptide exit tunnel or at the surface of the ribosome. A growing body of evidence suggests that the ribosome can alter the folding trajectory in many different ways. In this review, we summarize the recent examples of how translation affects folding of single-domain, multiple-domain and oligomeric proteins. The vectorial nature of translation, the spatial constraints of the exit tunnel, and the electrostatic properties of the ribosome-nascent peptide complex define the onset of early folding events. The ribosome can facilitate protein compaction, induce the formation of intermediates that are not observed in solution, or delay the onset of folding. Examples of single-domain proteins suggest that early compaction events can define the folding pathway for some types of domain structures. Folding of multi-domain proteins proceeds in a domain-wise fashion, with each domain having its role in stabilizing or destabilizing neighboring domains. Finally, the assembly of protein complexes can also begin cotranslationally. In all these cases, the ribosome helps the nascent protein to attain a native fold and avoid the kinetic traps of misfolding

Translational control by ribosome pausing in bacteria: How a non-uniform pace of translation affects protein production and folding

Protein homeostasis of bacterial cells is maintained by coordinated processes of protein production, folding, and degradation. Translational efficiency of a given mRNA depends on how often the ribosomes initiate synthesis of a new polypeptide and how quickly they read the coding sequence to produce a full-length protein. The pace of ribosomes along the mRNA is not uniform: periods of rapid synthesis are separated by pauses. Here, we summarize recent evidence on how ribosome pausing affects translational efficiency and protein folding. We discuss the factors that slow down translation elongation and affect the quality of the newly synthesized protein. Ribosome pausing emerges as important factor contributing to the regulatory programs that ensure the quality of the proteome and integrate the cellular and environmental cues into regulatory circuits of the cell

Translation error clusters induced by aminoglycoside antibiotics

Aminoglycoside antibiotics target the ribosome and induce mistranslation, yet which translation errors induce bacterial cell death is unclear. The analysis of cellular proteins by quantitative mass spectrometry shows that bactericidal aminoglycosides induce not only single translation errors, but also clusters of errors in full-length proteins in vivo with as many as four amino acid substitutions in a row. The downstream errors in a cluster are up to 10,000-fold more frequent than the first error and independent of the intracellular aminoglycoside concentration. The prevalence, length, and composition of error clusters depends not only on the misreading propensity of a given aminoglycoside, but also on its ability to inhibit ribosome translocation along the mRNA. Error clusters constitute a distinct class of misreading events in vivo that may provide the predominant source of proteotoxic stress at low aminoglycoside concentration, which is particularly important for the autocatalytic uptake of the drugs

EF-G-induced ribosome sliding along the noncoding mRNA.

Translational bypassing is a recoding event during which ribosomes slide over a noncoding region of the messenger RNA (mRNA) to synthesize one protein from two discontinuous reading frames. Structures in the mRNA orchestrate forward movement of the ribosome, but what causes ribosomes to start sliding remains unclear. Here, we show that elongation factor G (EF-G) triggers ribosome take-off by a pseudotranslocation event using a small mRNA stem-loop as an A-site transfer RNA mimic and requires hydrolysis of about two molecules of guanosine 5'-triphosphate per nucleotide of the noncoding gap. Bypassing ribosomes adopt a hyper-rotated conformation, also observed with ribosomes stalled by the SecM sequence, suggesting common ribosome dynamics during translation stalling. Our results demonstrate a new function of EF-G in promoting ribosome sliding along the mRNA, in contrast to codon-wise ribosome movement during canonical translation, and suggest a mechanism by which ribosomes could traverse untranslated parts of mRNAs

Ribosome rearrangements at the onset of translational bypassing.

Bypassing is a recoding event that leads to the translation of two distal open reading frames into a single polypeptide chain. We present the structure of a translating ribosome stalled at the bypassing take-off site of gene 60 of bacteriophage T4. The nascent peptide in the exit tunnel anchors the P-site peptidyl-tRNAGly to the ribosome and locks an inactive conformation of the peptidyl transferase center (PTC). The mRNA forms a short dynamic hairpin in the decoding site. The ribosomal subunits adopt a rolling conformation in which the rotation of the small subunit around its long axis causes the opening of the A-site region. Together, PTC conformation and mRNA structure safeguard against premature termination and read-through of the stop codon and reconfigure the ribosome to a state poised for take-off and sliding along the noncoding mRNA gap

A switch from α‐helical to β‐strand conformation during co‐translational protein folding

Cellular proteins begin to fold as they emerge from the ribosome.The folding landscape of nascent chains is not only shaped by theiramino acid sequence but also by the interactions with the ribo-some. Here, we combine biophysical methods with cryo-EM struc-ture determination to show that folding of aβ-barrel proteinbegins with formation of a dynamicα-helix inside the ribosome. Asthe growing peptide reaches the end of the tunnel, the N-terminalpart of the nascent chain refolds to aβ-hairpin structure thatremains dynamic until its release from the ribosome. Contactswith the ribosome and structure of the peptidyl transferase centerdepend on nascent chain conformation. These results indicate thatproteins may start out asα-helices inside the tunnel and switchinto their native folds only as they emerge from the ribosome.Moreover, the correlation of nascent chain conformations withreorientation of key residues of the ribosomal peptidyl-transferasecenter suggest that protein folding could modulate ribosome activity

ИЗУЧЕНИЕ ФЛОТАЦИОННЫХ СВОЙСТВ НОВЫХ СОБИРАТЕЛЕЙ ПРИ ОБОГАЩЕНИИ ШЕЕЛИТ-СУЛЬФИДНЫХ РУД

The article studies flotation properties of BTF-1552, IMA-206, and IMA-I413 alkali metal dialkyldithiophosphate samples. The article estimates beneficiation indices when using the reagent M-TF and its mixture with IMA-I413 and xanthogenate. On the basis of undertaken studies it was found that application of the mixture of IMA-I413 collectors with butyl xanthate at the ratio of 5 : 1 and the feed ratio of 20 + 5 g/t made it possible to increase the extraction into the copper concentrate: Cu by 0,79 %, Au by 4,1 % and Ag by 2,4, while the sulfide concentrate yield decreased by a factor of 2. The disadvantage of this reagent composition is the increase in As content in the copper concentrate by 0,67 %. Of all tested dialkyldithiophosphate samples, the best incremental indices of copper and noble metals recovery were obtained when using the BTF-1552collector. The extraction into the copper concentrate increased: Cu by 1,9 %, Au by 3,2 %, and Ag by 1,8 %, while the sulfide concentrate yield decreased by 1,4 times. The increase in As content in the copper concentrate was 0,34 %.Изучены флотационные свойства образцов диалкилдитиофасфатов щелочных металлов БТФ-1552, ИМА-206, ИМА-И413. Оценены показатели обогащения с использованием реагента М-ТФ и его смеси с ИМА-И413 и ксантогенатом. На основе выполненных исследований установлено, что применение смеси собирателей ИМА-И413 и бутилового ксантогената в соотношении 5 : 1 при расходе 20 + 5 г/т позволяет повысить извлечение в медный концентрат: Cu на 0,79 %, Au на 4,1 % и Ag на 2,4 %, при снижении выхода сульфидного концентрата в 2 раза. Недостатком данной композиции реагентов является рост содержания As в медном концентрате на 0,67 %. Из испытанных образцов диалкилдитиофосфатов лучшие показатели по приросту извлечения меди и благородных металлов получены на собирателе БТФ-1552. Извлечение в медный концентрат увеличилось: Cu на 1,9 %, Au на 3,2 % и Ag на 1,8 %, при снижении выхода сульфидного концентрата в 1,4 раза. Рост содержания As в медном концентрате составил 0,34 %

Intestinal microbiotes in children: conditionally healthy and who underwent intestinal resection

The article is devoted to the cultural research of the intestinal microbiota in children of the first year of life. In children who underwent intestinal resection (n=47), in comparison with conditionally healthy (n=121), higher levels of facultative-anaerobic conditionally pathogenic flora, in particular the Enterobacteriaceae group (E. coli lactose-negative) and hemolytic, Klebsiella spp., Enterobacter spp., Citrobacter spp.) and group Morganellaceae (Proteus spp.), as well as Staphylococcus aureus, with a lower content of anaerobes.Статья посвящена культуральному исследованию кишечной микробиоты у детей первого года жизни. У детей, перенесших резекцию кишечника(n=47), по сравнению с условно здоровыми (n=121), более высокие уровни факультативно-анаэробной условно патогенной флоры, в частности группы Enterobacteriaceae (E. coli лактозонегативная и гемолитическая; Klebsiella spp., Enterobacter spp., Citrobacter spp.) и группы Morganellaceae (Proteus spp.), а также Staphylococcus aureus, при меньшем содержании анаэробов

Translational recoding: Canonical translation mechanisms reinterpreted.

During canonical translation, the ribosome moves along an mRNA from the start to the stop codon in exact steps of one codon at a time. The collinearity of the mRNA and the protein sequence is essential for the quality of the cellular proteome. Spontaneous errors in decoding or translocation are rare and result in a deficient protein. However, dedicated recoding signals in the mRNA can reprogram the ribosome to read the message in alternative ways. This review summarizes the recent advances in understanding the mechanisms of three types of recoding events: stop-codon readthrough, -1 ribosome frameshifting and translational bypassing. Recoding events provide insights into alternative modes of ribosome dynamics that are potentially applicable to other non-canonical modes of prokaryotic and eukaryotic translation

Characteristic of the metabolic activity of the intestinal microbiota among the children of early age

In the article are presented data concerning study of the metabolic activity of the intestinal microbiota among the children aged from the neonatal period to three years old, who are conditionally healthy and belong to groups I and II of health classification. The dynamics of the content of short-chain fatty acids (FFA) in the feces have been analyzed, they are reflecting the activity of aerobic microbiota — acetic acid (C2); anaerobic microbiota — propionic (C3), butyric (C4) acid; the amount of acids (E); anaerobic index (AI) in newborn children, during the first year of life, in children of the second and third years of life. It is shown the differences in content of short-chain fatty acids in feces and their dynamics during the first three years of the child's life. It was found, that newborn children have higher activity indicators of obligate aerobic microflora, lower activity indicators of anaerobic processes and a higher level of total acid in feces. By the end of the third year of life, the metabolic activity of aerobic obligate flora decreases with a tendency to increase anaerobic processes, as evidenced by a decrease in the level of C2, an increase in C3, C4 and AI in the feces. The revealed features of the dynamics of the content of short-chain fatty acids in feces in young children reflect the process of formation of intestinal microbiota.В статье представлены данные об исследовании метаболической активности микробиоты кишечника у детей в возрасте от периода новорожденности до трех лет жизни, являющихся условно здоровыми и относящимися к I, II группам здоровья. Проанализирована динамика содержания короткоцепочечных жирных кислот (КЖК) в кале, отражающих активность аэробной микробиоты — уксусная кислота (С2); анаэробной микробиоты — пропионовая (С3), масляная (С4) кислоты; сумма кислот (Е); анаэробный индекс (АИ) у новорожденных детей, на протяжении первого года жизни, у детей второго и третьего года жизни. Показаны различия в содержании КЖК в кале и их динамика на протяжении первых трех лет жизни ребенка. Установлено, что новорожденные дети имеют более высокие показатели активности облигатной аэробной микрофлоры, более низкие показатели активности анаэробных процессов и более высокий уровень суммы кислот в кале. К концу третьего года жизни метаболическая активность аэробной облигатной флоры снижается при тенденции к увеличению анаэробных процессов, отражением чего является уменьшениеe уровня С2, нарастание С3, С4 и АИ в кале. Выявленные особенности динамики содержания КЖК в кале у детей раннего возраста являются отражением процесса становления микробиоты кишечник