Stability of domain structures in multi-domain proteins

Multi-domain proteins have many advantages with respect to stability and folding inside cells. Here we attempt to understand the intricate relationship between the domain-domain interactions and the stability of domains in isolation. We provide quantitative treatment and proof for prevailing intuitive ideas on the strategies employed by nature to stabilize otherwise unstable domains. We find that domains incapable of independent stability are stabilized by favourable interactions with tethered domains in the multi-domain context. Stability of such folds to exist independently is optimized by evolution. Specific residue mutations in the sites equivalent to inter-domain interface enhance the overall solvation, thereby stabilizing these domain folds independently. A few naturally occurring variants at these sites alter communication between domains and affect stability leading to disease manifestation. Our analysis provides safe guidelines for mutagenesis which have attractive applications in obtaining stable fragments and domain constructs essential for structural studies by crystallography and NMR

Effects of poling and crystallinity on the dielectric properties of Pb(In1/2Nb1/2)O3-Pb(Mg1/3Nb2/3)O3-PbTiO3 at cryogenic temperatures

The mechanisms underlying the anomalously large, room temperature piezoelectric activity of relaxor-PbTiO3 type single crystals have previously been linked to low temperature relaxations in the piezoelectric and dielectric properties. We investigate the properties of Pb(In1/2Nb1/2)O3-Pb(Mg1/3Nb2/3)O3-PbTiO3 between 10 and 300 K using dielectric permittivity measurements. We compare results on single crystal plates measured in the [001] and [111] directions with a polycrystalline ceramic of the same composition. Poled crystals have very different behaviour to unpoled crystals, whereas the dielectric spectrum of the polycrystalline ceramic changes very little on poling. A large, frequency dependent dielectric relaxation is seen in the poled [001] crystal around 100 K. The relaxation is much less prominent in the [111] cut crystal, and is not present in the polycrystalline ceramic. The unique presence of the large relaxation in poled, [001] oriented crystals indicates that the phenomenon is not due their relaxor nature alone. We propose that heterophase dynamics such as the motion of phase domain boundaries are responsible for both the anomalous electromechanical and dielectric behaviour

Investigation of halotolerant marine Staphylococcus sp. CO100, as a promising hydrocarbon-degrading and biosurfactant-producing bacterium, under saline conditions

A halotolerant strain CO100 of Staphylococcus sp. was isolated from contaminated sediments taken from the fishing harbour of Sfax, Tunisia, as an efficient hydrocarbonoclastic candidate. Strain CO100 exhibited a high capacity to break down almost 72% of the aliphatic hydrocarbons contained in crude oil (1%, v/v), used as the sole carbon and energy source, after 20 days of culture, at 100 g/l NaCl, 37 ◦C and 180 rpm. The isolate CO100 displayed also its ability to grow on phenanthrene, fluoranthene and pyrene (100 mg/l), at 100 g/l NaCl. Moreover, the isolate CO100 showed a notable aptitude to synthesize an efficient tensioactive agent namely BSCO100, on low-value substrates including residual frying oil and expired milk powder, thus reducing the high cost of biosurfactant production. The ESI/MS analysis designated that BS-CO100 belonged to lipopeptide class, in particular lichenysin and iturine members. Critical micelle concentrations of BS-CO100 were varying between 65 and 750 mg/l, depending on of the purity of the biosurfactant and the used carbon sources. BS-CO100 showed a high steadiness against a wide spectrum of pH (4.3-12), temperature (4-121 ◦C) and salinity (0-300 g/l NaCl), supporting its powerful tensioactive properties under various environmental conditions. Likewise, BS-CO100 exhibited no cytotoxic effect toward human HEK293 cells, at concentrations within 125 and 1000 μg/ml. Furthermore, the biosurfactant BS-CO100 exhibited remarkable anti-adhesive and anti-biofilm activities, being able to avoid and disrupt the biofilm formation by certain pathogenic microorganisms. In addition, BS-CO100 was found to have more potential to remove hydrocarbons from contaminated soils, compared to some chemical surfactants. In light of these promising findings, strain CO100, as well as its biosurfactant, could be successfully used in different biotechnological applications including the bioremediation of oil-polluted areas, even under saline conditions

Production, characterization and biotechnological potential of lipopeptide biosurfactants from a novel marine Bacillus stratosphericus strain FLU5

This work aimed to study the potential of a newly marine bacterium, Bacillus stratosphericus FLU5, to produce an efficient surface active agent BS-FLU5. Biosurfactant production was examined on different carbon sources using the surface tension measurement and the oil displacement test. Strain FLU5 showed its capacity to produce biosurfactants on the most of tested substrates and in particular the residual frying oil, which is an alternative, cheap and renewable carbon source, thus minimizing the high cost of producing surfactants. MALDI-TOF MS/MS analyses confirmed the presence of lipopeptides identified as members of surfactin and pumilacidin isomers. The critical micellar concentration of the purified lipopeptides produced by strain FLU5 was 50 mg/l and, at this concentration, the surface tension of the water was reduced from 72 to 28 mN/m. Furthermore, the crude lipopeptides showed interest stability against a broad range of pH (2.1-12), temperature (10-121 °C) and salinity (0-120 g/l NaCl). The biosurfactant BS-FLU5 demonstrated negligible cytotoxic effect against mammalian cells (HEK293 human embryonic kidney cell line) at all of tested concentration (125-1000 µg/ml). The application of BS-FLU5 in oil recovery from soil contaminated by hydrocarbons ( used motor oil) showed that it was more effective on the hydrocarbon-remobilization than some tested synthetic surfactants. These results highlight the applicability of the lipopeptides produced by the new marine Bacillus stratosphericus strain FLU5 in different fields, especially in environmental remediation processes. Production of lipopeptides is a characteristic of several Bacillus species, but to the best of our knowledge, this is the first report showing the potential of Bacillus stratosphericus for efficient production of biosurfactants or lipopeptides