Research Interests

Understanding and Engineering Multimodular Cellulase Systems

I am interested in the novel mechanisms by which newly discovered multimodular cellulase enzymes such as CelA interact with and degrade crystalline cellulose as well as whole biomass with an aim to design and optimize enhanced cellulase systems for overcoming biomass recalcitrance.

Most fungi and bacteria degrade plant cell walls by secreting free, complementary enzymes that hydrolyze cellulose; however, some bacteria use large enzymatic assemblies called cellulosomes, which recruit complementary enzymes to protein scaffolds. The thermophilic bacterium Caldicellulosiruptor bescii uses an intermediate strategy, secreting many free cellulases that contain multiple catalytic domains. One of these, CelA comprises a glycoside hydrolase family 9 and a family 48 catalytic domain, as well as three type III cellulose-binding modules. In the saccharification of a common cellulose standard, Avicel, CelA outperforms mixtures of commercially relevant exo and endoglucanases. From transmission electron microscopy studies of cellulose after incubation with CelA, we have discovered novel morphological features that suggest that CelA not only exploits the common surface ablation cellulose digestion mechanism driven by general cellulase processivity, but it also excavates extensive cavities into the surface of the substrate. These results suggest that natures repertoire of cellulose digestion paradigms remain only partially discovered and understood.

Plant Cell Wall Engineering and Recalcitrance Reduction

I am interested in the possible uses of glycoside hydrolase enzymes expressed in-planta to reduce plant cell wall recalcitrance. Current methods for introducing exogenous enzymes to biomass chips, as used today, are limited by multi-length scale diffusion barriers, both at the level of the biomass chip and the structure of the cell wall. There are multiple macro-scale and micro-scale factors contribute to the recalcitrance of lignocellulosic feedstock to both thermochemical pretreatment and subsequent enzymatic saccharification. On a micro-scale, important factors include the degree of lignification and the structural heterogeneity and complexity of cell-wall constituents such as cellulose microfibrils and matrix polymers such as xylan. In the past, in-planta expression of enzymes was primarily focused on addressing the enzyme cost problem by proposing to produce glycoside hydrolases (GH) in plants utilizing the plant itself as a bio-factory to produce large quantities of the enzymes, which would be extracted prior to pretreatment and then added back to the pretreated biomass to reduce the overall cost of the enzymatic hydrolysis.
Recently we have discovered that expressing a single endoglucanase in-planta can have profound effects on reducing the overall recalcitrance of the plant cell wall. Our functionally modified model crops were found to have reduced recalcitrance compared to wild type crops while maintaining a normal phenotype. And the effect was non-replicable by just adding back the enzyme after the plant had scenesed. The further advantage of these crops was that it was possible to reduce the thermochemical pre-treatment requirements of the plants significantly, offering large techno-economic advantages by using reduced severity pretreatments. These two factors make this recombinant plant technology an excellent starting point for developing sustainable energy production crops. 

Personal Profile

Senior Scientist, National Renewable Energy Laboratory (NREL), Chemical and Biosciences Center, 2012–present

Staff Scientist, NREL, Chemical and Biosciences Center, 2008–2012

Post-Doc, NREL, Chemical and Biosciences Center, 2008–2012

Education/Academic Qualification

PhD, Pharmacology, University of Colorado Anschutz Medical Campus

Bachelor, Biochemistry, University of Colorado Boulder


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