Pichia pastoris, an important methylotrophic yeast, is currently mainly used for the expression of recombinant proteins and has great potential applications in the production of value-added compounds (e.g., chemical and natural products). However, the construction of P. pastoris cell factories is largely hindered by the lack of genetic tools for the manipulation of multigene biosynthetic pathways. Therefore, the present study aimed to establish a CRISPR-based synthetic biology toolkit for the integration and assembly of multigene biosynthetic pathways into the chromosome of P. pastoris. First, 23 intergenic regions were selected and characterized as potential integration sites, with a focus on the integration efficiency and heterologous gene expression levels. In addition, a panel of constitutive and methanol-inducible promoters with different strengths (weak, medium, and strong promoters) were characterized to control the expression of biosynthetic pathway genes to the desirable levels. With a series of gRNA plasmids (for single-locus, two-loci, and three-loci integration) and donor plasmids (containing homology arms for integration and promoters and terminators for driving heterologous gene expression) as major components, a CRISPR-based synthetic biology toolkit was established, which enabled the integration of one locus, two loci, and three loci with efficiencies as high as ∼100, ∼93, and ∼75%, respectively, in P. pastoris GS115 strain. Finally, the application of the toolkit was demonstrated by the construction of a series of P. pastoris cell factories, which could produce 2,3-butanediol, β-carotene, zeaxanthin, and astaxanthin with methanol as the sole carbon and energy source. The P. pastoris synthetic biology toolkit is highly standardized and can be employed to construct P. pastoris cell factories with high efficiency.

There is a growing interest in establishing the methylotrophic yeast Pichia pastoris as microbial cell factories for producing fuels, chemicals, and natural products, particularly with methanol as the feedstock. Although CRISPR (Clustered Regularly Interspaced Short Palindromic Repeats) based genome editing technology has been established for the integration of multigene biosynthetic pathways, long (500−1000 bp) homology arms are generally required, probably due to low homologous recombination (HR) efficiency in P. pastoris. To achieve efficient genome integration of heterologous genes with short homology arms, we aimed to enhance HR efficiency by introducing the recombination machinery from Saccharomyces cerevisiae. First, we overexpressed HR related genes, including RAD52, RAD59, MRE11, and SAE2, and evaluated their effects on genome integration efficiency. Then, we constructed HR efficiency enhanced P. pastoris, which enabled single-, two-, and three-loci integration of heterologous gene expression cassettes with ∼40 bp homology arms with efficiencies as high as 100%, ∼98%, and ∼81%, respectively. Finally, we demonstrated the construction of β-carotene producing strain and the optimization of betaxanthin producing strain in a single step. The HR efficiency enhanced P. pastoris strains can be used for the construction of robust cell factories, and our machinery engineering strategy can be employed for the modification of other nonconventional yeasts.

BackgroundIron accumulation in basal ganglia accompanies neuronal loss in Huntington’s disease (HD) patients and mouse disease models. Disruption of HD brain iron homeostasis occurs before the onset of clinical signs. Therefore, investigating the mechanism of iron accumulation is essential to understanding its role in disease pathogenesis.MethodsN171-82Q HD transgenic mice brain iron was detected by using Diaminobenzidine-enhanced Perls’ stain. Iron homeostatic proteins including iron response protein 1 (IRP1), transferrin (Tf), ferritin and transferrin receptor (TfR) were determined by using western blotting and immunohistochemistry, and their relative expression levels of RNA were measured by RT-PCR in both N171-82Q HD transgenic mice and HEK293 cells expressing N-terminal of huntingtin.ResultsIron was increased in striatum and cortex of N171-82Q HD transgenic mice. Analysis of iron homeostatic proteins revealed increased expression of IRP1, Tf, ferritin and TfR in N171-82Q mice striatum and cortex. The same results were obtained in HEK293 cells expressing N-terminal of mutant huntingtin containing 160 CAG repeats.ConclusionWe conclude that mutant huntingtin may cause abnormal iron homeostatic pathways by increasing IRP1 expression in Huntington’s disease, suggesting potential therapeutic target.

Santalene, a major component of the sandalwood essential oil, is a typical representative of sesquiterpenes and has important applications in medicine, food, flavors, and other fields. Due to the limited supply of natural sandalwood resources, there is a growing interest in engineering microbial cell factories for the mass production of santalene. In the present study, Komagataella phaffii (also known as Pichia pastoris) was established as a cell factory for high-level production of α-santalene for the first time. The metabolic fluxes were rewired toward α-santalene biosynthesis through the optimization of promoters to drive the expression of the α-santalene synthase (SAS) gene, overexpression of the key mevalonate pathway genes (i.e., tHMG1, IDI1, and ERG20), and multicopy integration of the SAS expression cassette. In combination with medium optimization and bioprocess engineering, the optimal strain (STE-9) was able to produce α-santalene with a titer as high as 829.8 ± 70.6 mg/L, 4.4 ± 0.3 g/L, and 21.5 ± 1.6 g/L in a shake flask, batch fermenter, and fed-batch fermenter, respectively. These represented the highest production of α-santalene ever reported, highlighting the advantages of K. phaffii cell factories for the production of terpenoids and other natural products.

Guided by the theoretical calculation, achieving an efficient hydrogen evolution reaction (HER) by S-vacancy engineering toward MoS2-based materials is quite challenging due to the contradictory relationship between the adsorption free energy of hydrogen atoms (ΔG H) of the exposed Mo atoms (EMAs) and the number of EMAs per unit area (N EMAs). Herein, we demonstrate a novel one-pot incorporating-assisted compositing strategy to realize fine-tuning the concentration of S-vacancies (C S‑vacancies) of MoS2-based materials to boost highly active EMAs for efficient HER. In our strategy, S-vacancies are modulated into basal planes of MoS2 via decreasing the formation energy of S-vacancies by oxygen incorporation; moreover, C S‑vacancies of the basal planes is precisely regulated by simply controlling the molar amount of the Co precursor based on the electron injection effect. At low or excessively high C S‑vacancies, the as-synthesized electrocatalysts lack “highly active EMAs” in quantity or nature. The balance between the intrinsic activity of EMAs and N EMAs is realized for boosting EMAs with high catalytic performance. The optimal electrocatalysts exhibit excellent activity and stability at fine-tuning C S‑vacancies to 9.61%. Our results will pave a novel strategy for unlocking the potential of an inert basal plane in MoS2 for high-performance HER.

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Background Huntington’s disease (HD) is a neurodegenerative disease that involves a complex combination of psychiatric, cognitive and motor impairments. Synaptic dysfunction has been implicated in HD pathogenesis. However, the mechanisms have not been clearly delineated. Synaptic vesicular zinc is closely linked to modulating synaptic transmission and maintaining cognitive ability. It is significant to assess zinc homeostasis for further revealing the pathogenesis of synaptic dysfunction and cognitive impairment in HD. Results Histochemical staining by autometallography indicated that synaptic vesicular zinc was decreased in the hippocampus, cortex and striatum of N171-82Q HD transgenic mice. Analyses by immunohistochemistry, Western blot and RT-PCR found that the expression of zinc transporter 3 (ZnT3) required for transport of zinc into synaptic vesicles was obviously reduced in these three brain regions of the HD mice aged from 14 to 20 weeks  and  BHK  cells  expressing  mutant  huntingtin. Significantly, dual-luciferase reporter gene and chromatin immunoprecipitation assays demonstrated that transcription factor Sp1 could activate ZnT3 transcription via its binding to the GC boxes in ZnT3 promoter. Moreover, mutant huntingtin was found to inhibit the binding of Sp1 to the promoter of ZnT3 and down-regulate ZnT3 expression, and the decline in ZnT3 expression could be ameliorated through overexpression of Sp1. Conclusions This is first study to reveal a significant loss of synaptic vesicular zinc and a decline in ZnT3 transcriptional activity in the HD transgenic mice. Our work sheds a novel mechanistic insight into pathogenesis of HD that mutant huntingtin down-regulates expression of ZnT3 through inhibiting binding of Sp1 to the promoter of ZnT3 gene, causing disruption of synaptic vesicular zinc homeostasis. Disrupted vesicular zinc ultimately leads to early synaptic dysfunction and cognitive deficits in HD. It is also suggested that maintaining normal synaptic vesicular zinc concentration is a potential therapeutic strategy for HD.

Low or excessively high concentration of S-vacancy (CS-vacancy) is disadvantageous for the hydrogen evolution reaction (HER) activity of MoS2-based materials. Additionally, alkaline water electrolysis is most likely to be utilized in the industry. Consequently, it is of great importance for fine-tuning CS-vacancy to significantly improve alkaline hydrogen evolution. Herein, we have developed a one-step Ru doping coupled to compositing with CoS2 strategy to precisely regulate CS-vacancy of MoS2-based materials for highly efficient HER. In our strategy, Ru doping favors the heterogeneous nucleation and growth of CoS2, which leads to a high crystallinity of Ru-doped CoS2 (Ru-CoS2) and rich heterogeneous interfaces between Ru-CoS2 and Ru-doped MoS2-x (Ru-MoS2-x). This facilitates the electron transfer from Ru-CoS2 to Ru-MoS2-x, thereby increasing CS-vacancy of MoS2-based materials. Additionally, the electron injection effect increases gradually with an increase in the mass of Co precursor (mCo), which implies more S2- leaching from MoS2 at higher mCo. Subsequently, CS-vacancy of the as-synthesized samples is precisely regulated by the synergistic engineering of Ru doping and compositing with CoS2. At CS-vacancy = 17.1%, a balance between the intrinsic activity and the number of exposed Mo atoms (EMAs) to boost highly active EMAs should be realized. Therefore, the typical samples demonstrate excellent alkaline HER activity, such as a low overpotential of 170 mV at 100 mA cm−2 and a TOF of 4.29 s−1 at -0.2 V. Our results show promise for important applications in the fields of electrocatalysis or energy conversion.