Substrate Sequence Controls Regioselectivity of Lanthionine Formation by ProcM.

Lanthipeptides belong to the family of ribosomally synthesized and post-translationally modified peptides (RiPPs). The (methyl)lanthionine cross-links characteristic to lanthipeptides are essential for their stability and bioactivities. In most bacteria, lanthipeptides are maturated from single precursor peptides encoded in the corresponding biosynthetic gene clusters. However, cyanobacteria engage in combinatorial biosynthesis and encode as many as 80 substrate peptides with highly diverse sequences that are modified by a single lanthionine synthetase into lanthipeptides of different lengths and ring patterns. It is puzzling how a single enzyme could exert control over the cyclization processes of such a wide range of substrates. Here, we used a library of ProcA3.3 precursor peptide variants and show that it is not the enzyme ProcM but rather its substrate sequences that determine the regioselectivity of lanthionine formation. We also demonstrate the utility of trapped ion mobility spectrometry-tandem mass spectrometry (TIMS-MS/MS) as a fast and convenient method to efficiently separate lanthipeptide constitutional isomers, particularly in cases where the isomers cannot be resolved by conventional liquid chromatography. Our data allowed identification of factors that are important for the cyclization outcome, but also showed that there are no easily identifiable predictive rules for all sequences. Our findings provide a platform for future deep learning approaches to allow such prediction of ring patterns of products of combinatorial biosynthesis.

Alkali halide clusters produced by fast ion impact.

The most abundant geometries and relative stabilities of alkali halide clusters with a (XY)(n) (o) configuration (e.g., LiF, NaCl, KBr) are described. Five main series were obtained: linear, cyclic, cubic, arc strips and nanotubes. The stability analysis shows that higher members are likely to be formed from the lower member of the same series and/or from two building blocks (n = 1, 2). The energy analysis (D-plot) indicates that the most compact ones (e.g., cubic and nanotubes) present higher stability when compared to the linear, cyclic and arc strip structures; moreover, relative stability between the cubic and nanotube series varies with the cluster size.

Theoretical and experimental study of negative LiF clusters produced by fast ion impact on a polycrystalline 7LiF target.

The emission of negative cluster ions produced by the impact of approximately 60 MeV (252)Cf fission fragments on a (7)LiF polycrystalline target is analyzed. The negative ion mass spectrum is dominated by the ((7)LiF)(n)F(-) series, n = 1 to approximately 30. The desorption yield distribution of the ((7)LiF)(n)F(-) members has a maximum at n = 2 and then decreases as the sum of two exponentials whose decay parameters are k(Fast) = 0.9 and k(Slow) = 0.08. These k values are the same as those observed for the positive series and close to others obtained for condensed gas targets. Relative cluster ion stabilities, deduced from the experimental ion abundances for the (LiF)(n)F(-) series, are proposed to be correlated with theoretical structures according to their internal energy by using the deviation plot (D-plot) methodology. A pool of candidate cluster structures was generated using a genetic algorithm and further analyzed and optimized using density functional theory (DFT) with the hybrid functional B3LYP (DFT/B3LYP) and Moller-Plesset perturbation theory (MP2). For the small clusters (n = 1 to 2), the most stable structures are found to be linear, whereas the larger clusters (n = 4 to 6) present cubic or polyhedral structures. Fragmentation energies, ionization potentials, and relative stabilities are reported for the most abundant families of the (LiF)(n)F(-) and (LiF)(n)(-) series.

Characterization of (NH3)(n=1-6)NH+ clusters produced by 252Cf fragments impact onto a NH3 condensed target.

This paper reports the first characterization of the (NH(3))(n)NH+ cluster series produced by a 252Cf fission fragments (FF) impact onto a NH(3) ice target. The (NH(3))(n=1-6)NH+ members of this series have been analyzed theoretically and experimentally. Their ion desorption yields show an exponential dependence of the cluster population on its mass, presenting a relative higher abundance at n = 5. The results of DFT/B3LYP calculations show that two main series of ammonium clusters may be formed. Both series follow a clear pattern: each additional NH(3) group makes a new hydrogen bond with one of the hydrogen atoms of the respective {NH(3)NH}+ and {NH(2)NH(2)}+ cores. The energy analysis (i.e., D-plot and stability analysis) shows that the calculated members of the (NH(3))(n-1){NH(2)NH(2)}+ series are more stable than those of the (NH(3))(n-1){NH(3)NH}+ series. The trend on the relative stability of the members of more stable series, (NH(3))(n-1){NH(2)NH(2)}+, shows excellent agreement with the experimental distribution of cluster abundances. In particular, the (NH(3))4{NH(2)NH(2)}+ structure is the most stable one, in agreement with the experiments.

Mass spectroscopy investigation of the effect of gamma irradiation on the mean value of the number of ethoxy groups in the triton x-100 / Estudio del efecto de la radiación gamma en elvalor medio del número de grupos etoxiLados del surfactante Tritón X-100

El efecto de la radiación gamma proveniente de una fuente de 60Co en la estructura del surfactante no iónico Tritón X-100 fue investigado. Tres regiones principales pueden ser distinguidas en el comportamiento del valor medio del número de grupos etóxidos al aumentar la dosis. Sin embargo, el resultado global encontrado fue una pequeña variación en este valor medio al cambiar la dosis entre 0 y 70 KGy.

The effect of gamma radiation from a 60Co source on the structure of a nonionic surfactant, namely TRITON X-100, was investigated. Three main regions can be distinguished in the behavior of the mean value of ethoxy groups with an increase in the absorbed dose. However just a slightly decrease on this mean value was obtained when the dose range from 0 to 70 kGy.