A Novel Regulated Hybrid Promoter That Permits Autoinduction of Heterologous Protein Expression in Kluyveromyces lactis.

The yeast Kluyveromyces lactis has been a successful host for the production of heterologous proteins for over 30 years. Currently, the galactose-/lactose-inducible and glucose-repressible LAC4 promoter (P LAC4 ) is the most widely used promoter to drive recombinant protein expression in K. lactis However, P LAC4 is not fully repressed in the presence of glucose and significant protein expression still occurs. Thus, P LAC4 is not suitable in processes where tight regulation of heterologous gene expression is required. In this study, we devised a novel K. lactis promoter system that is both strong and tightly controllable. We first tested several different endogenous K. lactis promoters for their ability to express recombinant proteins. A novel hybrid promoter (termed P350) was created by combining segments of two K. lactis promoters, namely, the strong constitutive P GAP1 promoter and the carbon source-sensitive P ICL1 promoter. We demonstrate that P350 is tightly repressed in the presence of glucose or glycerol and becomes derepressed upon depletion of these compounds by the growing cells. We further illustrate the utility of P350-controlled protein expression in shake flask and high-cell-density bioreactor cultivation strategies. The P350 hybrid promoter is a strong derepressible promoter for use in autoinduction of one-step fermentation processes for the production of heterologous proteins in K. lactisIMPORTANCE The yeast Kluyveromyces lactis is an important host for the expression of recombinant proteins at both laboratory and industrial scales. However, the system lacks a tightly regulated promoter that permits controlled expression of heterologous proteins. In this study, we report the engineering of a highly regulated strong hybrid promoter (termed P350) for use in K. lactis P350 is tightly repressed by glucose or glycerol in the medium but strongly promotes gene expression once the carbon source has been consumed by the cells. This feature permits heterologous protein expression to be "autoinduced" at any scale without the addition of a gratuitous inducer molecule or changing feed solutions.

Determinants of elephant foraging behaviour in a coupled human-natural system: Is brown the new green?

Crop raiding by wildlife poses major threats to both wildlife conservation and human well-being in agroecosystems worldwide. These threats are particularly acute in many parts of Africa, where crop raiders include globally threatened megafauna such as elephants, and where smallholder agriculture is a primary source of human livelihood. One framework for understanding herbivore feeding behaviour, the forage-maturation hypothesis, predicts that herbivores should align their movements with intermediate forage biomass (i.e., peak green-up); this phenomenon is known as "surfing the green wave." Crop-raiding elephants, however, often consume not just foliage, but also fruits and tubers (e.g., maize and potatoes), which generally mature after seasonal peaks in photosynthetic activity. Thus, although elephants have been reported to surf the green wave in natural habitats, they may utilize a different strategy in cultivated landscapes by selecting crops that are "browning down." We sought to understand the factors that underpin movement of elephants into agricultural landscapes. In Mozambique's Gorongosa National Park, we used movement data from GPS-collared elephants, together with precipitation records, remotely sensed estimates of landscape greenness (NDVI), DNA-based diet analysis, measurements of plant nutritional quality and survey-based metrics of crop availability to understand spatiotemporal variation in elephant crop-raiding behaviour. Elephants tracked peak NDVI while foraging inside the Park. During the dry season, however, when NDVI within the Park declined and availability of mature crops was high, crop raiding increased dramatically, and elephants consistently selected crop plants that were browning down while foraging in cultivated landscapes. Crops contained significantly higher digestible energy than wild food plants, but comparable (and sometimes lower) levels of digestible protein, suggesting that this foraging strategy maximized energy rather than protein intake. Our study is the first to combine GPS tracking data with high-resolution diet analysis and community-based reporting of crop availability to reveal fine-scale plasticity in foraging behaviour of elephants at the human-wildlife interface. Our results extend the forage-maturation hypothesis by showing that elephants surf waves of plant brown-down in cultivated landscapes. These findings can aid efforts to reduce human-elephant conflict by enabling wildlife managers to prioritize mitigation actions in time and space with limited resources.

Structure of the trehalose-6-phosphate phosphatase from Brugia malayi reveals key design principles for anthelmintic drugs.

Parasitic nematodes are responsible for devastating illnesses that plague many of the world's poorest populations indigenous to the tropical areas of developing nations. Among these diseases is lymphatic filariasis, a major cause of permanent and long-term disability. Proteins essential to nematodes that do not have mammalian counterparts represent targets for therapeutic inhibitor discovery. One promising target is trehalose-6-phosphate phosphatase (T6PP) from Brugia malayi. In the model nematode Caenorhabditis elegans, T6PP is essential for survival due to the toxic effect(s) of the accumulation of trehalose 6-phosphate. T6PP has also been shown to be essential in Mycobacterium tuberculosis. We determined the X-ray crystal structure of T6PP from B. malayi. The protein structure revealed a stabilizing N-terminal MIT-like domain and a catalytic C-terminal C2B-type HAD phosphatase fold. Structure-guided mutagenesis, combined with kinetic analyses using a designed competitive inhibitor, trehalose 6-sulfate, identified five residues important for binding and catalysis. This structure-function analysis along with computational mapping provided the basis for the proposed model of the T6PP-trehalose 6-phosphate complex. The model indicates a substrate-binding mode wherein shape complementarity and van der Waals interactions drive recognition. The mode of binding is in sharp contrast to the homolog sucrose-6-phosphate phosphatase where extensive hydrogen-bond interactions are made to the substrate. Together these results suggest that high-affinity inhibitors will be bi-dentate, taking advantage of substrate-like binding to the phosphoryl-binding pocket while simultaneously utilizing non-native binding to the trehalose pocket. The conservation of the key residues that enforce the shape of the substrate pocket in T6PP enzymes suggest that development of broad-range anthelmintic and antibacterial therapeutics employing this platform may be possible.

Atomizing into a chilled extraction solvent eliminates liquid gas from a spray-freeze drying microencapsulation process.

A spray-freeze drying encapsulation process using direct atomization into a chilled extraction solvent (ACES), in the absence of liquefied gas, was developed. Heat transfer models, developed to estimate droplet freezing time (t(f)), identified ACES conditions where solvent extraction, nonsolvent influx, and droplet deformation were minimized. Calculated t(f)'s for dichloromethane and dichloroethane droplets were 98 and 46 ms, respectively, using atomization into liquid nitrogen (ALN2). For droplets <100 microm, this was shorter than the calculated headspace residence time, indicating freezing precedes cryogen impact. Calculated t(f)'s for ACES ranged from 9 to 36 ms. The longest t(f)'s resulted in collapsed, asymmetric particles with phase-separated cores and high nonsolvent residuals (>10%). Intermediate t(f)'s produced spherical-cap particles with rough exteriors and a mixture of solid and phase-separated structures. The shortest t(f)'s produced smooth, spherical-cap particles with solid cores, resembling particles made by ALN2; residual solvent levels were similar or superior to those with ALN2. Phase separation within droplets, induced upon extraction solvent contact in ACES, was minimized for cases where t(f) or=1.3. These results, obtained with cryogen temperatures up to -122 degrees C, demonstrate encapsulation by ACES is possible if freezing is sufficiently rapid, enabling milder operating temperatures.

Enhanced bioavailability of a poorly soluble VR1 antagonist using an amorphous solid dispersion approach: a case study.

Amorphous solid dispersions (ASD) of a poorly soluble water-soluble VR1 antagonist (AMG 517) were explored for improving physical stability and in vivo exposure. AMG 517 was incorporated at 15 or 50 wt % into polymeric microparticles of hydroxypropyl methylcellulose acetate succinate (HPMCAS) and hydroxypropyl methylcellulose (HPMC) by spray-drying. Solid particles having a collapsed, corrugated structure were observed by SEM. Median particle size ranged from 29 to 40 microm by laser light scattering, and residual solvent levels were below 2% by thermal gravimetric analysis. ASD powders exhibited single glass transition temperatures (Tg) in the range of 98-117 degrees C by modulated DSC and were amorphous by XRPD. Amorphous stability, characterized at 40 degrees C/75% RH (open dish) by XRPD, was at least six months for ASD formulations. Drug dissolution and supersaturation testing in a USP-2 apparatus indicated superior performance of ASD formulations over micronized AMG 517. PK of an ASD formulation in capsule (15 wt % AMG 517 in HPMCAS blended with 5 wt % SDS) in cynomolgus monkeys (n = 6, crossover) increased AUC 163% and Cmax 145% in comparison to an OraPlus suspension control. The study demonstrates the ASD approach provides improved amorphous physical stability and oral bioavailability for a poorly soluble development-stage molecule.