Papers by Robert Standaert
Advanced Materials Interfaces, May 1, 2019
Biophysical Journal, Feb 1, 2018
Metabolic pathway assembly typically involves the expression of enzymes from multiple organisms i... more Metabolic pathway assembly typically involves the expression of enzymes from multiple organisms in a single heterologous host. Ensuring that each enzyme functions effectively can be challenging, since many potential factors can disrupt proper pathway flux. These challenges are amplified when the enzymes are expressed at single copy from the chromosome. We have explored these issues using 4-hydroxybenzoate monooxygenase homologs heterologously expressed in Escherichia coli. Initial chromosomal enzyme expression was insufficient to support consistent growth with 4-hydroxybenzoate. Experimental evolution identified mutations that improved pathway activity. One set of mutations was common between homologs, while a second class of mutations was homolog-specific. Ultimately, we were able to identify a set of mutations that provided sufficient activity for growth with 4-hydroxybenzoate while maintaining or improving growth with protocatechuate. These findings demonstrate the potential for flexible, scalable chromosomal pathway engineering, as well as the value of directed evolution strategies to rapidly identify and overcome diverse factors limiting enzyme activity.
Scientific Reports, Jul 16, 2019
Background Down-regulation of the caffeic acid 3-O-methyltransferase EC 2.1.1.68 (COMT) gene in t... more Background Down-regulation of the caffeic acid 3-O-methyltransferase EC 2.1.1.68 (COMT) gene in the lignin biosynthetic pathway of switchgrass (Panicum virgatum) resulted in cell walls of transgenic plants releasing more constituent sugars after pretreatment by dilute acid and treatment with glycosyl hydrolases from an added enzyme preparation and from Clostridium thermocellum. Fermentation of both wild-type and transgenic switchgrass after milder hot water pretreatment with no water washing showed that only the transgenic switchgrass inhibited C. thermocellum. Gas chromatography–mass spectrometry (GCMS)-based metabolomics were undertaken on cell wall aqueous extracts to determine the nature of the microbial inhibitors. Results GCMS confirmed the increased concentration of a number of phenolic acids and aldehydes that are known inhibitors of microbial fermentation. Metabolomic analyses of the transgenic biomass additionally revealed the presence of a novel monolignol-like metabolite...
Structural studies with the importin alpha complexed with nuclear localization sequence peptidomimetics
FEBS Journal, 2005
Solvent Extraction and Ion Exchange, 2017
Separation Science and Technology, 2019
Separation of 225 Ra (t 1/2 = 15 d) from its daughter isotope 225 Ac (t 1/2 = 10 d) is necessary ... more Separation of 225 Ra (t 1/2 = 15 d) from its daughter isotope 225 Ac (t 1/2 = 10 d) is necessary to obtain pure 225 Ac for cancer alpha-therapy. In this study, microscale separation of 225 Ra from its daughter 225 Ac using BioRad AG50X4 cation exchange resin was achieved with good reproducibility across microdevices, and ≥90% purity was achieved for 225 Ac, which is comparable to conventional chromatography. These results indicate the potential for greater use of microfluidics for biomedical radiochemistry. The modularity of the system and its compatibility with different resins allows for quick and easy adaptation to the various needs of a separation campaign.
Advanced Materials Interfaces, 2019
Advanced Materials Interfaces, 2019
Micro‐ and nanofabricated sample environments are useful tools for characterizing diffusion in co... more Micro‐ and nanofabricated sample environments are useful tools for characterizing diffusion in confined aqueous environments. The steady‐state diffusion and adsorption of unilamellar lipid vesicles in arrays of hydrophilic micropillars is investigated. Gradients in the coverage of fluorescently labeled, pillar‐supported lipid films, formed from vesicle fusion, are determined from 3D z‐stack images using confocal microscopy. The gradients are the result of preferential adsorption of vesicles near the tops of the pillars, which progressively deplete them from solution as they diffuse toward the base of the array. However, the increased propensity for vesicle adsorption near the pillar tops compared to the confined spaces between pillars results in the formation of confluent supported lipid bilayers at the pillar tops that resist the adsorption of additional vesicles while leaving the pillar surfaces below available for binding. This results in a reduction in the numbers of depleted ve...
Journal of proteome research, Jan 26, 2018
Indole-3-acetic acid (IAA) plays a central role in plant growth and development, and many plant-a... more Indole-3-acetic acid (IAA) plays a central role in plant growth and development, and many plant-associated microbes produce IAA using tryptophan as the precursor. Using genomic analyses, we predicted that Pantoea sp. YR343, a microbe isolated from Populus deltoides, synthesizes IAA using the indole-3-pyruvate (IPA) pathway. To better understand IAA biosynthesis and the effects of IAA exposure on cell physiology, we characterized proteomes of Pantoea sp. YR343 grown in the presence of tryptophan or IAA. Exposure to IAA resulted in upregulation of proteins predicted to function in carbohydrate and amino acid transport and exopolysaccharide (EPS) biosynthesis. Metabolite profiles of wild-type cells showed the production of IPA, IAA, and tryptophol, consistent with an active IPA pathway. Finally, we constructed an ΔipdC mutant that showed the elimination of tryptophol, consistent with a loss of IpdC activity, but was still able to produce IAA (20% of wild-type levels). Although we faile...
The Journal of organic chemistry, Jan 21, 2016
Primary alcohols can be deoxygenated cleanly and in yields of 60-95% by reduction of derived diph... more Primary alcohols can be deoxygenated cleanly and in yields of 60-95% by reduction of derived diphenyl phosphate esters with lithium triethylborohydride in tetrahydrofuran at room temperature. Selective deoxygenation of a primary alcohol in the presence of a secondary alcohol was demonstrated. The two-step process can be performed in one pot, making it simple and convenient.
Langmuir : the ACS journal of surfaces and colloids, May 29, 2016
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Papers by Robert Standaert