Lattice defects induced by microtubule-stabilizing agents exert a long-range effect on microtubule growth by promoting catastrophes

Microtubules are dynamic cytoskeletal polymers that spontaneously switch between phases of growth and shrinkage. The probability of transitioning from growth to shrinkage, termed catastrophe, increases with microtubule age, but the underlying mechanisms are poorly understood. Here, we set out to test whether microtubule lattice defects formed during polymerization can affect growth at the plus end. To generate microtubules with lattice defects, we used microtubule-stabilizing agents that promote formation of polymers with different protofilament numbers. By employing different agents during nucleation of stable microtubule seeds and the subsequent polymerization phase, we could reproducibly induce switches in protofilament number and induce stable lattice defects. Such drug-induced defects led to frequent catastrophes, which were not observed when microtubules were grown in the same conditions but without a protofilament number mismatch. Microtubule severing at the site of the defect was sufficient to suppress catastrophes. We conclude that structural defects within the microtubule lattice can exert effects that can propagate over long distances and affect the dynamic state of the microtubule end.

The use of Near-Infrared Spectroscopy to evaluate the effect of exercise on peripheral muscle oxygenation in patients with lower-extremity artery disease: a systematic review

Funding Acknowledgements Type of funding sources: None. Background Near-Infrared Spectroscopy (NIRS) has been suggested as a new diagnostic tool in patients with lower-extremity artery disease (LEAD). The aim of this systematic review was i) to summarize the impact of exercise therapy on lower-limb muscle oxygenation, evaluated by means of NIRS, in patients with LEAD and ii) to give an overview on NIRS instruments and methodology. Methods A systematic search was conducted in MEDLINE and Embase, from the earliest date available until 16th of March 2020, to identify peer-reviewed studies involving the use of NIRS in the evaluation of exercise training on muscle oxygenation in patients with LEAD. Primary outcomes were NIRS-derived variables. Effect sizes were calculated as standardized mean differences. Assessment of methodological quality was done using a combined checklist from the Cochrane bias and the quality assessment tool for before-after studies without control group. Results Eleven original trials were included involving 16 exercise groups and 4 control groups. Tissue saturation index (TSI) at rest remained unchanged following the exercise interventions. Yet, exercise training increased time-to-minimum TSI during exercise (range effect sizes: +0.172 to +0.927). In addition, exercise training led to a faster recovery to half and full TSI rest values in most intervention groups (range effect sizes: -0.046 to -0.558 and -0.269 to -0.665 respectively). Finally, NIRS data reproducibility and analytic methods were underreported in the included studies. To illustrate, only four studies reported appropriate measures to ensure repeated reproducible probe positioning. The use of raw or filtered data for analysis was reported in none of the included articles. Conclusion The available NIRS data suggest that exercise training improves deoxygenation and reoxygenation patterns in patients with LEAD. Whereas NIRS is a promising tool in the evaluation of LEAD, the low number of RCT’s as well as large heterogeneity in NIRS assessment methods, outcome measures and instrumentation, warrants more research to better understand the role of muscle oxygenation associated with exercise-induced improvements in walking capacity. In particular the role of NIRS to study underlying mechanisms and determinants related to exercise progression in LEAD patients is appealing. Abstract Figure. NIRS during treadmill test

Response of Benthic Diatom Assemblages to Contamination by Metals in a Marine Environment

Studies on marine benthic diatoms in environments contaminated by metals are scarce. The typical structure of benthic diatom assemblages (species richness, diversity, dominance, dominant taxa) from undisturbed environments may be used as reference for contrasting with contaminated environments in order to observe how said assemblages respond to such disturbance. Thus, the Ho that the structure of benthic diatom associations and morphology of their frustules under contamination by metals would be normal, as in unpolluted environments was tested. To do this, concentrations of 24 metals were surveyed in a coastal zone impacted by mining residues, and the structure of benthic local diatom assemblages was described. Metal concentrations measurements for 15 metals surpassed the normal values of the upper earth cortex, seven were under the low range effect, and three (Cd, Cu, Zn) surpassed the medium range effect values. At a control site no element concentration was above the reference values for low range effect (LRE) or medium range effect (MRE) standards. There, diatom species richness (S) was high, particularly on seaweeds; where, 397 diatom taxa were recorded. In contrast, at the contaminated area 217 diatom taxa were recorded, but diversity (H’) ranged from 2.4 to 4.3. Relative high frequencies of deformed diatom valves mainly of Achnanthes spp. were recorded in contaminated sediments. In general, diatom taxocenoses presented a typical structure for non-contaminated environments. However, scarceness of specimens, lower S, and frequency of deformed valves suggest responses to metal contamination. For marine environments, the latter values corresponding to A. longipes may be considered a reliable reference to the response of benthic diatoms to metal contamination.

Population dynamics and structural effects at short and long range support the hypothesis of the selective advantage of the G614 SARS-Cov2 spike variant

SARS-CoV-2 epidemics quickly propagated worldwide, sorting virus genomic variants in newly established propagules of infections. Stochasticity in transmission within and between countries or an actual selective advantage could explain the global high frequency reached by some genomic variants. Using statistical analyses, demographic reconstructions, and molecular dynamics simulations, we show that the globally invasive G614 spike variant i) underwent a significant demographic expansion in most countries not explained by stochastic effects nor by overrepresentation in clinical samples; ii) increases the spike S1/S2 furin-like site conformational plasticity (short-range effect), and iii) modifies the internal motion of the receptor-binding domain affecting its cross-connection with other functional domains (long-range effect). Our results support the hypothesis of a selective advantage at the basis of the spread of the G614 variant, which we suggest may be due to structural modification of the spike protein at the S1/S2 proteolytic site, and provides structural information to guide the design of variant-specific drugs.

Fulleropyrrolidines with orthogonally flexible substituents - synthesis and electrochemical properties

A large series of disubstituted fulleropyrrolidines was synthesized and analyzed by the cyclic voltammetry. The three main groups of target compounds differ by a flexible N-chain, while their further diversity was achieved by the introduction of various rigid, aryl substituents at pyrrolidine carbon. Some dialkyl analogues were designed for comparison, as well. A standard [3+2]-cycloaddition of in situ generated azomethine ylides to C60 afforded a variety of disubstituted fulleropyrrolidines. Furthermore, a set of dumbbell-shaped di(fulleropyrrolidine) derivatives containing rigid fumaryl or isophthaloyl diamide platform was prepared in aim to investigate a long-range effect of the second fulleropyrrolidine moiety on electrochemical properties. All compounds were fully characterized by comparative analysis of spectral data, while examination of electrochemical properties was performed on representative samples, distinguished by main structural subunits. All compounds expressed quite similar electron-accepting ability, lower than C60, but higher in comparison to structurally similar N-methylfulleropyrrolidine.