The sarcomere-based structure of muscles is conserved among vertebrates; however, vertebrate muscle physiology is extremely diverse. A molecular explanation for this diversity and its evolution has not been proposed. We use phylogenetic analyses and single-molecule force spectroscopy (smFS) to investigate the mechanochemical evolution of titin, a giant protein responsible for the elasticity of muscle filaments. We resurrect eight-domain fragments of titin corresponding to the common ancestors to mammals, sauropsids, and tetrapods, which lived 105-356 Myr ago, and compare them with titin fragments from some of their modern descendants. We demonstrate that the resurrected titin molecules are rich in disulfide bonds and display high mechanical stability. These mechanochemical elements have changed over time, creating a paleomechanical trend that seems to correlate with animal body size, allowing us to estimate the sizes of extinct species. We hypothesize that mechanical adjustments in titin contributed to physiological changes that allowed the muscular development and diversity of modern tetrapods.

The barley HvAACT1 gene codes for a citrate transporter associated with tolerance to acidic soil. In this report, we describe a single nucleotide polymorphism (SNP) in the HvAACT1 coding region that was detected as T-1,198 (in genotypes with lower root growth on acidic soil) or G-1,198 (greater root growth) and resulted in a single amino acid change (L/V-172). Molecular dynamic analysis predicted that HvAACT1 proteins with L or V-172 were stable, although the substitution led to structural changes within the protein. To evaluate the effect of the SNP on tolerance to acidic soil, barley accessions were separated into haplotypes based on the presence of a 1 kb insertion in the HvAACT1 promoter and a 21 bp insertion/deletion. These markers and the SNP-1,198 allowed the identification of five haplotypes. Short-term soil experiments showed no difference in root growth for most of the accessions containing the 21 bp insertion and T or G-1,198. In contrast, genotypes showing both the 21 bp deletion and G-1,198, with one of them having the 1 kb insertion, showed greater root growth. These results indicate that the SNP was not advantageous or deleterious when genotypes from the same haplotype were compared. The occurrence of the SNP was highly correlated with the 21 bp insertion/deletion that, together with the 1 kb insertion, explained most of the barley tolerance to acidic soil.

No abstract

The present work attempt to explore systematically the surfactant sorption at liquid-liquid interfaces with coarse-grained models targeting thermodynamic properties of reference liquid solutions. We employ dissipative particle dynamics with soft-core forcefield tested against experimental data on micellization of surfactants in water, and the previous results are reproduced in this work. We consider three different nonionic surfactants: hexaethylene glycol monododecyl ether (C12E6), 2-[4-(2,4,4-trimethylpentan-2-yl)phenoxy]ethanol) knows as Triton X-100 (TХ-100), and two alkyl glucoside surfactants (CnG1) with n-alkane tail fragments and a saccharide hydrophilic head at decane-water and toluene-water interfaces. For TX-100, we composed a model based on the literature forcefield and found a good agreement with the experimental CMC. The head-head interactions are of different origins for different surfactant groups: entropic repulsion between ethylene oxide chains of C12E6 and TX-100, and more chemically specific and complex interactions between the maltose heads of alkyl glucosides. We interpret our results with the Redlich-Peterson equation of monolayer adsorption in order to relate the adsorption to the bulk concentration of the surfactant and the interfacial tension. The densities of the adsorbed monolayer at CMC mostly agree with the experimental data, and a reasonable agreement was obtained for the interfacial tension at CMC. At the same time, we found significant discrepancies between the simulated and experimental adsorption isotherms. We explain them by the oversimplified forcefield: when the parameters are fitted to the free energies of bulk solutions, they may not correctly reproduce the interfacial free energies.

No abstract