NMR-Metabolomic Profiling and Genome Mining Drive the Discovery of Cyclic Decapeptides from a Marine Streptomyces.

The integration of NMR-metabolomic and genomic analyses can provide enhanced identification of structural properties as well as key biosynthetic information, thus achieving the targeted discovery of new natural products. For this purpose, NMR-based metabolomic profiling of the marine-derived Streptomyces sp. S063 (CGMCC 14582) was performed, by which N-methylated peptides possessing unusual negative 1H NMR chemical shift values were tracked. Meanwhile, genome mining of this strain revealed the presence of an unknown NRPS gene cluster (len) with piperazic-acid-encoding genes (lenE and lenF). Under the guidance of the combined information, two cyclic decapeptides, lenziamides D1 (1) and B1 (2), were isolated from Streptomyces sp. S063, which contains piperazic acids with negative 1H NMR values. The structures of 1 and 2 were determined by extensive spectroscopic analysis combined with Marfey's method and ECD calculations. Furthermore, we provided a detailed model of lenziamide (1 and 2) biosynthesis in Streptomyces sp. S063. In the cytotoxicity evaluation, 1 and 2 showed moderate growth inhibition against the human cancer cells HEL, H1975, H1299, and drug-resistant A549-taxol with IC50 values of 8-24 µM.

A comprehensive calibration method for non-orthogonal error and scale factor error of triaxial Helmholtz coil.

In order to calibrate the non-orthogonal error and scale factor error of triaxial Helmholtz coil, a comprehensive error calibration method is proposed in this paper. The comprehensive error model is established first, and then the method to generate a frequency-controllable spatial rotating magnetic field whose magnetic field intensity is constant based on triaxial Helmholtz coil is introduced. Based on the fact that the magnetic field intensity generated by the current through the coil is constant, the objective function is constructed and the error parameters are solved using the least-squares fitting method. Simulation experiments and field tests prove the effectiveness and feasibility of this method. The most obvious finding to emerge from this study is that the proposed method is not only suitable for the electromagnetic shielding room environment but also suitable for the field tests in the presence of a background geomagnetic field far away from urban electricity interference. The root mean square error value is reduced to 0.7 nT from 298.2 nT in the electromagnetic shielding room, and it is reduced to 0.8 nT from 299.0 nT in the wild. Compared to the two-step calibration method, the proposed method reduces the sampling time by controlling the frequency of the rotating magnetic field and reduces the influence of the changes of the background geomagnetic field on the experimental results. This method has better anti-interference ability. Because the modulus of the background geomagnetic field has no effect on this method, it gets rid of the dependence on large current or background geomagnetic field shielding devices. Comparative experiments and repetitive experiments verify the practicability and stability of this method.