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The diterpenoid paclitaxel (Taxol®) is a blockbuster anticancer agent that was originally isolated from the Pacific yew (Taxus brevifolia) five decades ago. Despite the wealth of information gained over the years on Taxol research, there still remains supply issues to meet increasing clinical demand. Although alternative Taxol production methods have been developed, they still face several drawbacks that cause supply shortages and high production costs. It is highly desired to develop biotechnological production platforms for Taxol, however, there are still gaps in our understanding of the biosynthetic pathway, catalytic enzymes, regulatory and control mechanisms that hamper production of this critical drug by synthetic biology approaches. Over the past 5 years, significant advances were made in metabolic engineering and optimization of the Taxol pathway in different hosts, leading to accumulation of taxane intermediates. Computational and experimental approaches were leveraged to gain mechanistic insights into the catalytic cycle of pathway enzymes and guide rational protein engineering efforts to improve catalytic fitness and substrate/product specificity, especially of the cytochrome P450s (CYP450s). Notable breakthroughs were also realized in engineering the pathway in plant hosts that are more promising in addressing the challenging CYP450 chemistry. Here, we review these recent advances and in addition, we summarize recent transcriptomic data sets of Taxus species and elicited culture cells, and give a bird’s-eye view of the information that can be gleaned from these publicly available resources. Recent mining of transcriptome data sets led to discovery of two putative pathway enzymes, provided many lead candidates for the missing steps and provided new insights on the regulatory mechanisms governing Taxol biosynthesis. All these inferences are relevant to future biotechnological production of Taxol.

The main-chain thermotropic liquid crystalline polymer (LCP), Vectra A950, has been reported to be able to simultaneously lower dynamic friction coefficient and wear rate when introduced into poly(vinylidene fluoride) (PVDF) as lubricant. In this investigation, we evaluate the friction surfaces of Vectra A950 through atomic force microscopy (AFM), spectroscopy and nanoindentation. By AFM, various frozen nanometer-level textures are observed at friction surfaces of LCP particles after cessation of friction. Besides, orientation and microscopic hardness of textures for Vectra A950 are unveiled via polarized Raman spectroscopy and nanoindentation tests, respectively. It is worth noting that as an important hint of orientation for LCPs under shear, observation of LCPs textures is conventionally conducted at molten state by polarized-light optical microscope and shear apparatus, however, which hardly detects textures morphology at solid state. Overall, this investigation not only proposes a new approach to evaluate textures of LCPs, but also provides guide for further exploring tribological enhancement mechanism of LCPs.

Although main-chain thermotropic liquid crystalline polymer (LCP) has been extensively investigated as self-reinforcing composites, tribological application is rarely reported. This paper explores tribological enhancement effect of LCP on representative matrix poly (vinylidene fluoride) (PVDF). Moreover, structures of PVDF/LCP blends are assessed in detail. Due to immiscibility, LCP in blends is uniformly dispersed in the form of particles or microfibrils, dependent on LCP content. Besides, LCP improves storage modulus of PVDF. Most importantly, tribological performance of PVDF is obviously promoted. Compared with neat PVDF, the wear rate, coefficient of friction and oscillation amplitude of blend containing 20 wt% LCP simultaneously decrease by 97.7%, 80.7% and 80.2%, respectively. In particular, frequency-enhancement phenomenon is observed. By probing worn PVDF domains with nanoindentation test and atomic force microscopy (AFM), preliminary tribological enhancement mechanism of LCP is unveiled. Overall, this finding provides a new, but promising lubrication route of polymer.

5-Deoxy(iso)flavonoids are structural representatives of phenylpropanoid-derived compounds and play critical roles in plant ecophysiology. Recently, 5-deoxy(iso)flavonoids gained significant interest due to their potential applications as pharmaceuticals, nutraceuticals, and food additives. Given the difficulties in their isolation from native plant sources, engineered biosynthesis of 5-deoxy(iso)flavonoids in a microbial host is a highly promising alternative approach. However, the production of 5-deoxy(iso)flavonoids is hindered by metabolic flux imbalances that result in a product profile predominated by non-reduced analogues. In this study, GmCHS7 (chalcone synthase from Glycine max) and GuCHR (chalcone reductase from Glycyrrhizza uralensis) were preliminarily utilized to improve the CHR ratio (CHR product to total CHS product). The use of this enzyme combination improved the final CHR ratio from 39.7% to 50.3%. For further optimization, a protein-protein interaction strategy was employed, basing on the spatial adhesion of GmCHS7:PDZ and GuCHR:PDZlig. This strategy further increased the ratio towards the CHR-derived product (54.7%), suggesting partial success of redirecting metabolic flux towards the reduced branch. To further increase the total carbon metabolic flux, 15 protein scaffolds were programmed with stoichiometric arrangement of the three sequential catalysts GmCHS7, GuCHR and MsCHI (chalcone isomerase from Medicago sativa), resulting in a 1.4-fold increase in total flavanone production, from 69.4 mg/L to 97.0 mg/L in shake flasks. The protein self-assembly strategy also improved the production and direction of the lineage-specific compounds 7,4′-dihydroxyflavone and daidzein in Escherichia coli. This study presents a significant advancement of 5-deoxy(iso)flavonoid production and provides the foundation for production of value-added 5-deoxy(iso)flavonoids in microbial hosts., Highlights • 5-Deoxyflavonoids synthetic pathways were constructed and engineered in E. coli. • CHR ratio was optimized by orthologous enzyme selection, and CHS-CHR interaction. • Artificial scaffold P4S2G1 was programmed to improve the total metabolic flux. • Daidzein and genistein were synthesized from L-tyr in E. coli for the first time.

A three-step strategy was employed to prepare a self-lubricating and anti-wear graphene oxide/nano-MoS2 (GO/nano-MoS2, abbreviated GMS) hybrid by chemical compounding as a novel multidimensional assembly. This development aims to overcome the high friction coefficient of GO/polymer composites and to explore the variations in the tribological properties stemming from the different nanoparticles immobilized on the GO surface. The as-prepared GMS was incorporated into a polyimide (PI) matrix to yield GMS/PI composites by in situ polymerization. The mechanical, thermodynamic, surface, and tribological properties of the GMS/PI composites were investigated, and the synergistic effects of the abovementioned properties between nano-MoS2 and GO were discussed in detail. A homogeneous dispersion of GMS, a suppressive and protective effect of graphene sheets, a rolling friction effect of the detached nano-MoS2 particles, and a transfer film composed of MoS2 were achieved herein, contributing to the enhanced tribological properties. The differences in the enhancement effects of nanohybrids can be mainly attributed to two aspects: the intrinsic characteristics of the assembled nanoparticles and the combinational structure of the multidimensional assemblies.

Modified graphene/carbon nanotube (abbreviated GCNT) assemblies were prepared by chemical compounding from amino-functionalized graphene (abbreviated MG) and carboxyl-functionalized multi-walled carbon nanotube (abbreviated MCNT). Diverse hybrid structures, such as graphene-shelled CNT microspheres, graphene/CNT interlayers and CNT-coated graphene nanosheets, have been obtained by adjusting the reaction ratio of the two precursor particles. The as-prepared GCNTs were incorporated into polyimide (PI) matrix to yield GCNT/PI composites by in situ polymerization. The mechanical, thermo-mechanical and tribological properties of GCNT/PI composites were investigated and synergistic effects in terms of lubrication and wear resistance have been acquired. The friction coefficient and wear rate decreased by 29.3% and 75.8%, respectively, with only 0.5 wt% addition of GCNT14 (WMG/WMCNT = 1 : 4), compared to virgin PI. The results indicate that combinational structure of multidimensional assemblies has a great influence on the enhancement performance and tribological mechanism of nanocomposites.