Computational investigation on MB<Subscript><Emphasis Type="Italic">n</Emphasis></Subscript> (M = Li-Cs,Be-Ba,Sc-La and Ti; <Emphasis Type="Italic">n</Emphasis> = 28 and 38)

Differing from the weakly antiaromatic B₈₀ buckyball, the medium-sized C ₁–B₂₈ and D _2h –B₃₈, as well as their mono- to tetra-anions, are highly aromatic, as indicated by the negative nucleus-independent chemical shifts (NICSs) at their cage centers. The interior cavities and high aromaticity of the B₂₈ and B₃₈ cages render them very promising hosts to accommodate diverse metal atoms. Accordingly, we carried out systematic density functional theory (DFT) computations on the structures, stabilities and electronic properties of metalloborofullerenes MB _n (M?=?Li, Na, K, Rb, Cs, Be, Mg, Ca, Sr, Ba, Sc, Y, La and Ti; n?=?28 and 38). Among them, besides the recently reported M@B₃₈(M?=?Sc, Y and Ti) [Lu et al. (2015) Phys Chem Chem Phys 17:20897–20902], Ti@B₂₈ and M@B₃₈ (M?=?Ca and La) also favor endohedral structures with large binding energies, and are suggested promising targets for experimental applications. Note that Ti@B₂₈ is the first endohedral derivative based on the new B₂₈ fullerene, and La@B₃₈ features the largest metal size inside a B₃₈ cage thus far. These endohedral derivatives, as exemplified by Ca@B₃₈, may exhibit σ and π double aromaticity over the whole cage surface, indicating their considerable stability. In contrast, the other metals prefer to reside at the exterior cage surface, due mainly to the mismatch of their sizes with the boron cages, though the size match is not the only factor to determine their doping form. Furthermore, the infrared absorption spectra and ¹¹B nuclear magnetic resonance spectra of the three new M@B _n complexes were computed to assist future experimental characterization.

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Graphical Abstract Putting more metals into medium-sized boron cages!

     

A new paradigm of DNA synthesis: three-metal-ion catalysis

Enzyme catalysis has been studied for over a century. How it actually occurs has not been visualized until recently. By combining in crystallo reaction and X-ray diffraction analysis of reaction intermediates, we have obtained unprecedented atomic details of the DNA synthesis process. Contrary to the established theory that enzyme-substrate complexes and transition states have identical atomic composition and catalysis occurs by the two-metal-ion mechanism, we have discovered that an additional divalent cation has to be captured en route to product formation. Unlike the canonical two metal ions, which are coordinated by DNA polymerases, this third metal ion is free of enzyme coordination. Its location between the α- and β-phosphates of dNTP suggests that the third metal ion may drive the phosphoryltransfer from the leaving group opposite to the 3′-OH nucleophile. Experimental data indicate that binding of the third metal ion may be the rate-limiting step in DNA synthesis and the free energy associated with the metal-ion binding can overcome the activation barrier to the DNA synthesis reaction.     

Prediction of Cascading Failures in Spatial Networks

Cascading overload failures are widely found in large-scale parallel systems and remain a major threat to system reliability; therefore, they are of great concern to maintainers and managers of different systems. Accurate cascading failure prediction can provide useful information to help control networks. However, for a large, gradually growing network with increasing complexity, it is often impractical to explore the behavior of a single node from the perspective of failure propagation. Fortunately, overload failures that propagate through a network exhibit certain spatial-temporal correlations, which allows the study of a group of nodes that share common spatial and temporal characteristics. Therefore, in this study, we seek to predict the failure rates of nodes in a given group using machine-learning methods.We simulated overload failure propagations in a weighted lattice network that start with a center attack and predicted the failure percentages of different groups of nodes that are separated by a given distance. The experimental results of a feedforward neural network (FNN), a recurrent neural network (RNN) and support vector regression (SVR) all show that these different models can accurately predict the similar behavior of nodes in a given group during cascading overload propagation.     

Crystal Structure of Human Myotubularin-Related Protein 1 Provides Insight into the Structural Basis of Substrate Specificity

Myotubularin-related protein 1 (MTMR1) is a phosphatase that belongs to the tyrosine/dual-specificity phosphatase superfamily. MTMR1 has been shown to use phosphatidylinositol 3-monophosphate (PI(3)P) and/or phosphatidylinositol 3,5-bisphosphate (PI(3,5)P₂) as substrates. Here, we determined the crystal structure of human MTMR1. The refined model consists of the Pleckstrin homology (PH)-GRAM and phosphatase (PTP) domains. The overall structure was highly similar to the previously reported MTMR2 structure. Interestingly, two phosphate molecules were coordinated by strictly conserved residues located in the C(X)₅R motif of the active site. Additionally, our biochemical studies confirmed the substrate specificity of MTMR1 for PI(3)P and PI(3,5)P₂ over other phosphatidylinositol phosphates. Our structural and enzymatic analyses provide insight into the catalytic mechanism and biochemical properties of MTMR1.     

Dual Effect of Phenolic Nectar on Three Floral Visitors of Elsholtzia rugulosa (Lamiaceae) in SW China

Some plants secrete toxic nectar to appeal to most effective pollinators and deter non-pollinators or nectar thieves; however available information about ecological function of toxic nectar remains scarce. Elsholtzia rugulosa stands out as a plant with toxic nectar recorded in SW China. We focused on the functional significance of the phenolic compound that imparts toxic to the nectar of E. rugulosa. The effects of phenolic nectar were studied in three visitors of the flowers of the winter-blooming E. rugulosa Hemsl. (Lamiaceae) in SW China. The pollinating species Apis cerana Fabricius (Apidae; Asian honey bee) and two occasional visitors, Vespa velutina Lepeletier (Vespidae; yellow-legged Asian hornet) and Bombus eximius Smith (Apidae; a bumble bee) were tested for their preferences for low and high concentrations of 4-hydroxybenzoic acid in hexose and sucrose solutions. The pollinator is important for the plant, which is dependent on pollinator visits to attain a higher seed production and it is most likely that the combination of phenolic toxic nectar and the adaptation to phenolic nectar by A. cerana delivers an evolutionary advantage to both actors. The low and high concentrations of the phenolic acid were nearly totally refused by both occasional visitors V. velutina and B. eximius and were preferred by the pollinator A. cerana. E. rugulosa gains by having a much higher seed production and the pollinating honey bee by having an exclusive and reliable food source during the winter season at high altitudes in SW China. We found that the function of the toxic phenolic compound has dual roles by appealing to legitimate pollinators and deterring non-pollinators of E. rugulosa.     

Discovery of piRNAs Pathway Associated with Early-Stage Spermatogenesis in Chicken

Piwi-interacting RNAs (piRNAs) play a key role in spermatogenesis. Here, we describe the piRNAs profiling of primordial germ cells (PGCs), spermatogonial stem cells (SSCs), and the spermatogonium (Sp) during early-stage spermatogenesis in chicken. We obtained 31,361,989 reads from PGCs, 31,757,666 reads from SSCs, and 46,448,327 reads from Sp cells. The length distribution of piRNAs in the three samples showed peaks at 33 nt. The resulting genes were subsequently annotated against the Gene Ontology (GO) database. Five genes (RPL7A, HSPA8, Pum1, CPXM2, and PRKCA) were found to be involved in cellular processes. Interactive pathway analysis (IPA) further revealed three important pathways in early-stage spermatogenesis including the FGF, Wnt, and EGF receptor signaling pathways. The gene Pum1 was found to promote germline stem cell proliferation, but it also plays a role in spermatogenesis. In conclusion, we revealed characteristics of piRNAs during early spermatogonial development in chicken and provided the basis for future research.