The alcohol oxidase 1 (AOX1) promoter (PAOX1) of Pichia pastoris is the most powerful and commonly used promoter for driving protein expression. However, mechanisms regulating its transcriptional activity are unclear. Here, we identified a Zn(II)2Cys6-type methanol-induced transcription factor 1 (Mit1) and elucidated its roles in regulating PAOX1 activity in response to glycerol and methanol. Mit1 regulated the expression of many genes involved in methanol utilization pathway, including AOX1, but did not participate in peroxisome proliferation and transportation of peroxisomal proteins during methanol metabolism. Structural analysis of Mit1 by performing domain deletions confirmed its specific and critical role in the strict repression of PAOX1 in glycerol medium. Importantly, Mit1, Mxr1, and Prm1, which positively regulated PAOX1 in response to methanol, were bound to PAOX1 at different sites and did not interact with each other. However, these factors cooperatively activated PAOX1 through a cascade. Mxr1 mainly functioned during carbon derepression, whereas Mit1 and Prm1 functioned during methanol induction, with Prm1 transmitting methanol signal to Mit1 by binding to the MIT1 promoter (PMIT1), thus increasingly expressing Mit1 and subsequently activating PAOX1.

A series of catalysts containing of gold-palladium bimetallic nanoparticles (Au-Pd NPs in the range of 1-6 nm) anchored on foam-like mesoporous silica were used for the aerobic oxidation of benzyl alcohol. A remarkable synergistic effect was observed on these Au-Pd NPs catalysts prepared by one-pot method. Both the experimental and theoretical study revealed a close relationship between the surface PdO species on the catalysts and their catalytic performance, that is, a higher surface PdO content leads to a lower catalytic activity. The surface content of PdO species on the catalysts could be tuned by controlling the Au/Pd ratios, because the formation of Au-Pd alloy NPs and electron transfer between surface Au and Pd atoms prevented the oxidation of surface Pd and retarded the formation of PdO species. An optimal Au/Pd ratio of 1/4.5 on the foam-like mesoporous silica support was obtained, with nearly no surface PdO species formed and resulted the highest benzyl alcohol conversion of 96%.The bimetallic Au-Pd catalysts exhibited much higher catalytic activity for benzyl alcohol oxidation (TOF = 50000 -60000 h -1 ) than the monometallic Pd catalyst (TOF = 12500 h -1 ) on which surface Pd is easily oxidized to PdO. These results provide direct evidence for the synergistic effect of the Au-Pd bimetallic catalyst in benzyl alcohol oxidation.

Ruthenium (Ru) nanoparticles dispersed in mesoporous carbon microfibers were prepared using alumina microfibers as the templates via a chemical vapour deposition (CVD) route. Characterized data showed that Ru nanoparticles were embedded in the mesoporous carbon matrix. The samples were found to possess a specific surface area as high as 750 m(2) g(-1), pore sizes in the range of 3-5 nm, lengths in the range of 5-10 μm, and a width of about 0.5 μm. The Ru catalysts displayed a remarkably high catalytic activity and an excellent stability in the hydrogenation of D-glucose. The observed good catalyst performance is attributed to the carbon microfiber morphology, unblocked mesoporous structure, and the hydrogen spillover effect induced by the unique surface contact between the Ru nanoparticles and the carbon. In addition, the incorporation of nitrogen significantly improved the catalytic performance due to the enhanced hydrogen adsorption, better wettability, and modified electronic properties of the Ru.

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Homogeneous immobilization of gold nanoparticles (Au NPs) on mesoporous silica has been achieved by using a one-pot synthesis method in the presence of organosilane mercapto-propyl-trimethoxysilane (MPTMS). The resultant Au NPs exhibited an excellent catalytic activity in the solvent-free selective oxidation of cyclohexane using molecular oxygen. By establishing the structure-performance relationship, the origin of the high activity of mesoporous supported Au catalyst was identified to be due to the presence of low-coordinated Au (0) sites with high dispersion. Au NPs were confirmed to play a critical role in the catalytic oxidation of cyclohexane by promoting the activation of O2 molecules and accelerating the formation of surface-active oxygen species.

Mesoporous aluminas with a uniform fibrous morphology were synthesized using a copolymer-controlled homogeneous precipitation method under hydrothermal conditions. Scanning electron microscopy, X-ray diffraction, solid-state magic-angle spinning nuclear magnetic resonance, transmission electron microscopy, thermogravimetric analysis, nitrogen adsorption, Fourier transform infrared spectrometry, and elemental analysis techniques were used to characterize the samples. The effect of various synthesis conditions on the morphology and mesoporous structure of the alumina fibers was investigated. Such porous alumina microfibers may find applications in nanotechnology and catalysis. They can also be used as advanced high-temperature composite materials and templates for fabrication of fibrous materials of various compositions, such as carbon, transition-metal oxides, and polymers.

Clewlike ZnO superstructures were synthesized using a copolymer-controlled self-assembly method in the presence of urea. The structural properties were investigated using X-ray diffraction, scanning electron microscopy, transmission electron microscopy, and selected-area electron diffraction techniques. It was observed that the concentrations of the copolymer and urea are the key parameters determining the superstructure morphology. Experimental data also showed that the copolymer has played a dual function in the self-assembly process; namely, one is to control the oriented attachment of the nanoparticles, and the other is to stabilize the superstructures. Room-temperature photoluminescence data showed interesting optical properties of the ZnO superstructures.

In this work, the identification and characterization of two hexose transporter homologs in the methylotrophic yeast Pichia pastoris, P. pastoris Hxt1 (PpHxt1) and PpHxt2, are described. When expressed in a Saccharomyces cerevisiae hxt-null mutant strain that is unable to take up monosaccharides, either protein restored growth on glucose or fructose. Both PpHXT genes are transcriptionally regulated by glucose. Transcript levels of PpHXT1 are induced by high levels of glucose, whereas transcript levels of PpHXT2 are relatively lower and are fully induced by low levels of glucose. In addition, PpHxt2 plays an important role in glycolysis-dependent fermentative growth, since PpHxt2 is essential for growth on glucose or fructose when respiration is inhibited. Notably, we firstly found that the deletion of PpHXT1, but not PpHXT2, leads to the induced expression of the alcohol oxidase I gene (AOX1) in response to glucose or fructose. We also elucidated that a sharp dropping of the sugar-induced expression level of Aox at a later growth phase is caused mainly by pexophagy, a degradation pathway in methylotrophic yeast. The sugar-inducible AOX1 promoter in an ⌬hxt1 strain may be promising as a host for the expression of heterologous proteins. The functional analysis of these two hexose transporters is the first step in elucidating the mechanisms of sugar metabolism and catabolite repression in P. pastoris.Pichia pastoris, a methylotrophic yeast, has been developed as a successful expression platform for heterologous proteins. The increasing popularity of this particular expression system can be attributed to several reasons (3, 6): (i) the easy techniques needed for the molecular genetic manipulation and the simple growth medium or culture conditions required for growth compared with those for mammalian cells; (ii) high levels of protein expression at the intra-or extracellular level; (iii) the ability to perform higher-eukaryotic protein modifications, such as glycosylation, disulfide bond formation, and proteolytic processing; and (iv) the availability of the expression system as a commercially available kit.In the P. pastoris system, the expression of foreign genes is usually driven by the outstanding promoter of the alcohol oxidase I gene (AOX1), which encodes the first enzyme in the methanol utilization pathway. The expression of Aox can be regulated with both repression and derepression mechanisms responding to different carbon sources. The AOX1 promoter (P AOX1 ) is induced only in response to methanol and repressed by other carbon sources, such as glucose or ethanol (3, 5, 6). However, the P AOX1 -based platform is not free of drawbacks (12, 23). The strength of induction of P AOX1 is strictly dependent on methanol as the carbon source. Methanol is derived mainly from petrochemical sources, which is unsuitable for use in the production of certain food products and additives. Methanol metabolism in methylotrophic yeast produces a toxic byproduct, hydrogen peroxide (H 2 O 2 ), which causes oxidative stress and eli...