Structural and mechanistic investigations on CC bond forming α-oxoamine synthase allowing L-glutamate as substrate.

Carbon­carbon (C-C) bonds serve as the fundamental structural backbone of organic molecules. As a critical CC bond forming enzyme, α-oxoamine synthase is responsible for the synthesis of α-amino ketones by performing the condensation reaction between amino acids and acyl-CoAs. We previously identified an α-oxoamine synthase (AOS), named as Alb29, involved in albogrisin biosynthesis in Streptomyces albogriseolus MGR072. This enzyme belongs to the α-oxoamine synthase family, a subfamily under the pyridoxal 5'-phosphate (PLP) dependent enzyme superfamily. In this study, we report the crystal structures of Alb29 bound to PLP and L-Glu, which provide the atomic-level structural insights into the substrate recognition by Alb29. We discover that Alb29 can catalyze the amino transformation from L-Gln to L-Glu, besides the condensation of L-Glu with ß-methylcrotonyl coenzyme A. Subsequent structural analysis has revealed that one flexible loop in Alb29 plays an important role in both amino transformation and condensation. Based on the crystal structure of the S87G mutant in the loop region, we capture two distinct conformations of the flexible loop in the active site, compared with the wild-type Alb29. Our study offers valuable insights into the catalytic mechanism underlying substrate recognition of Alb29.

[Effects of Different Topdressing Nitrogen Rates on Soil Fungal Community Structure and Ecological Network in Wheat Field Under Crop Residue Retention].

Crop residue retention and fertilizer application are the main sources of soil nutrient input in fields. Crop residue retention combined with appropriate fertilizer application rates could provide necessary nutrients for crop production under the premise of environmentally friendly conditions. The aim of this study was to clarify the influence of different topdressing nitrogen rates on the soil fungal community in a wheat field under crop residue retention and to evaluate the rationality of nitrogen fertilizer management in winter wheat from the perspective of soil ecological function. On the basis of full straw retention and 150 kg·hm-2 basal nitrogen, treatments with five topdressing nitrogen rates (0, 37.5, 75, 112.5, and 150 kg·hm-2) were set up. The abundance, diversity, structure, and ecological network of soil fungal communities were analyzed using real-time fluorescence quantitative PCR and high-throughput sequencing, and the main soil physical and chemical factors driving the change in soil fungal communities were explored. The results showed that, compared with the no topdressing nitrogen and low topdressing nitrogen rate treatments, high topdressing nitrogen rate treatments increased soil total nitrogen and mineral nitrogen and decreased soil pH, total phosphorus, available phosphorus, and available potassium. Compared with the no topdressing nitrogen treatments, the 37.5-150 kg·hm-2 topdressing nitrogen treatments significantly increased soil fungal community abundance (P<0.05), whereas there was no significant difference among different topdressing nitrogen treatments (P>0.05). The Heip index and Shannon index of soil fungal communities decreased gradually with the increase in topdressing nitrogen rate, and the Sobs index, Heip index, and Shannon index of soil fungal communities in the treatment with 150 kg·hm-2 topdressing nitrogen were significantly lower than those of 0-75 kg·hm-2 topdressing nitrogen treatments (P<0.05). Principal component analysis and similarity analysis showed that there were significant differences in soil fungal community structure under different topdressing nitrogen rate treatments (P<0.05). With the increase in topdressing nitrogen rate, the number of network edges and average number of neighbors of soil fungal ecological network increased first and then decreased, and the network complexity of 37.5 kg·hm-2 topdressing nitrogen treatments was the highest. Compared with 0-75 kg·hm-2 topdressing nitrogen treatments, 112.5 kg·hm-2 and 150 kg·hm-2 topdressing nitrogen treatments increased the characteristic path length of the soil fungal ecological network, whereas it decreased the network density. With the increase in topdressing nitrogen rate, the relative abundance of soil saprotrophs gradually increased, and the pathotroph-saprotroph-symbiotroph relative abundance gradually decreased. Redundancy analysis showed that soil pH, total phosphorus, mineral nitrogen, available phosphorus, and available potassium were the main soil physicochemical factors affecting the soil fungal community structure in the wheat field under different topdressing nitrogen rate treatments. In conclusion, on the basis of straw retention and basal nitrogen, topdressing nitrogen at the wheat jointing stage could change the diversity, structure, and species composition of the soil fungal community, in turn affecting the soil fungal ecological network and function, and high topdressing nitrogen rates could reduce soil fungal community diversity, ecological network complexity, and network density.

Design, synthesis, and evaluation of antitumor activity of novel C-6 sulfhydryl-substituted and 20-substituted derivatives of celastrol.

Celastrol has been identified as a potential candidate for anticancer drug development. In this study, 28 novel celastrol derivatives with C-6 sulfhydryl substitution and 20-substitution were designed and synthesized, and their antiproliferative activity against human cancer cells and non-malignant human cells was evaluated, with cisplatin and celastrol being used as controls. The results showed that most of the derivatives had enhanced in vitro anticancer activity compared to the parent compound celastrol. Specifically, derivative 2f demonstrated the most potent inhibitory potential and selectivity against HOS with an IC50 value of 0.82 µM. Our study provides new insights into the structure-activity relationship of celastrol and suggests that compound 2f may be a promising drug candidate for the treatment of osteosarcoma.

[Soil bacterial communities of different crop rotations and yield of succeeding wheat.] / 不同轮作茬口土壤细菌群落及后茬小麦产量.

Evaluating ecological sustainability and crop productivity of different crop rotation patterns could provide theoretical support for adjusting and optimizing crop planting structure. We set seven treatments with different rotation crops and periods. We used real-time quantitative PCR to determine the abundance of soil bacterial community and 16S rRNA gene amplicon high-throughput sequencing technology to analyze diversity and taxa composition of soil bacterial community. Both soil available nutrients and succeeding wheat yield were measured. The results showed that, compared with the rotation with summer maize, the rotations with summer peanut or soybean in diffe-rent periods reduced soil organic carbon, mineral nitrogen, and available potassium, but significantly increased soil available phosphorus. The 16S rRNA gene copy numbers of soil bacteria in the treatments of rotations with summer peanut or soybean in different periods were significantly decreased, while community richness and diversity were increased. Different rotation crops significantly changed the structure and taxonomic composition of soil bacterial community. Compared with the rotation with summer maize, the rotations with summer soybean in different periods significantly increased the 1000-grain weight and grain yield of succeeding winter wheat. In conclusion, rotations with summer peanut or soybean in different periods could increase soil available phosphorus content and bacterial diversity, and significantly change soil bacterial community structure. In particular, rotation with summer soybean performed best in promoting yield formation of succeeding winter wheat.

[Response of Soil Fungal Communities in Diversified Rotations of Wheat and Different Crops].

Crop-soil microorganism interactions and feedback are critical to soil health and crop production. The aim of this study was to clarify the difference in soil fungal communities under diversified rotations of wheat and different crops in the North China Plain and to provide a theoretical basis for the construction and optimization of ecological sustainable planting systems. The soil fungal community abundance, composition, and diversity of continuous winter wheat-summer maize M, winter wheat-summer peanut (summer maize) PM, and winter wheat-summer soybean (summer maize) SM treatments were studied using real-time quantitative PCR and high-throughput sequencing technology. The results showed that, compared with those of the continuous winter wheat-summer maize treatment, the peanut rotation treatment PM2 and soybean rotation treatment SM2 significantly reduced soil fungal ITS sequence copy numbers (P<0.05); there was no significant difference in soil fungal ITS sequence copy numbers between other rotation treatments and those of the control (P>0.05). Rotation treatments with peanut or soybean increased soil fungal community richness (Chao1 and ACE indices) and diversity (Shannon and InvSimson indices), in which the community richness of all rotation treatments and the community diversity of SM1/SM2 treatments varied significantly (P<0.05). The result of non-metric multidimensional scaling (NMDS) analysis showed that the soil fungal community among different rotation crops were obviously separated. The rotation crops significantly affected soil fungal community structure (PERMANOVA:r2=0.350, P=0.001; ANOSIM:r=0.478, P=0.001). Ascomycota (73.67%-85.48%) was the dominant phylum, whereas Sordariomycetes (30.53%-48.19%) and Eurotiomycetes (11.12%-31.19%) were the dominant classes of the fungal communities of sandy-loam fluvo-aquic soil in the North China Plain. There were significantly different taxa of soil fungal communities in different rotations. Potential pathogens such as Neocosmospora, Plectosphaerella, and Gibellulopsis were significantly enriched in the rotations of winter wheat-summer peanut (summer maize), whereas potential beneficial fungi such as Penicillium and Zopfiella were significantly enriched in the rotations of winter wheat-summer soybean (summer maize). Compared with that under the continuous winter wheat-summer maize treatment, rotations with peanut or soybean increased the relative abundance of pathotroph, pathotroph-symbiotroph, and saprotroph-symbiotroph fungi and decreased the relative abundance of saprotroph fungi. The soil fungal community richness and structure were significantly related to soil organic carbon and available nutrients, and the Shannon diversity index was significantly related to soil mineral nitrogen and available phosphorus. In summary, on the basis of continuous winter wheat-summer maize rotation in the North China Plain, adding summer peanut or summer soybean instead of summer maize for rotations with different interval years could increase the richness and diversity of soil fungal communities and significantly change soil fungal community structure. In particular, summer soybean as the preceding crop had a positive effect on the enrichment of potential beneficial fungi.