Biology subjects

Chundawat, S. P. S.

Publications and source records attributed to Chundawat, S. P. S..

5 recordsLinked to original sources

bioRxiv2020

Reduced type-A carbohydrate-binding module interactions to cellulose leads to improved endocellulase activity

Dissociation of non-productively bound cellulolytic enzymes from cellulose is hypothesized to be a key rate-limiting factor impeding cost-effective biomass conversion to fermentable sugars. However, the role of carbohydrate-binding modules (CBMs) in enabling non-productive enzyme binding is not well understood. Here, we examine the subtle interplay of CBM binding and cellulose hydrolysis activity for three model Type-A CBMs (families 1, 3a, and 64) tethered to a multifunctional endoglucanase (CelE) on two distinct cellulose allomorphs (i.e., cellulose I and III). We generated a small-library of mutant CBMs with varying cellulose affinity, as determined by equilibrium binding assays, followed by monitoring cellulose hydrolysis activity of CelE-CBM fusion constructs. Finally, kinetic binding assays using quartz crystal microbalance with dissipation (QCM-D) were employed to measure CBM adsorption and desorption rate constants Kon and Koff, respectively, towards nanocrystalline cellulose derived from both allomorphs. Overall, our results indicate that reduced CBM equilibrium binding affinity towards cellulose I alone, resulting from increased desorption rates (Koff) and reduced effective adsorption rates (nKon), is correlated to overall improved endocellulase activity. Future studies could employ similar approaches to unravel the role of CBMs in non-productive enzyme binding and develop improved cellulolytic enzymes for industrial applications.Competing Interest StatementShishir P.S. Chundawat declares a conflict of interest and competing financial interest(s) having filed two patent applications on pretreatment processes to produce cellulose-III enriched cellulosic biomass for biofuels production (US20130244293A1and WO2011133571A2). All other authors declare that they have no competing interests.View Full Text

biochemistry↗

bioRxiv2020

Comparison of analytical methods for rapid & reliable quantification of plant-based carbohydrates for the quintessential bioenergy educator

Biochemical conversion of plant-based insoluble carbohydrate polymers, such as starch from corn grains or cellulose-hemicellulose from corn stover, into soluble fermentable sugars (e.g., glucose and xylose) for bioenergy production has seen tremendous research activity and commercial-scale biorefineries deployment over the last three decades, particularly in regions around the world that have a dominant agricultural-based economy. Therefore, educators in schools and universities have developed various hands-on experimental activities to engage the general public and students either in outreach events or lab/classroom-based settings to instruct students on various inter-disciplinary concepts relevant to bioenergy and biochemicals production. One of the limitations of most available protocols is the lack of systematic and comprehensive comparison of educator-friendly analytical tools and protocols for quantitative analysis of water-soluble carbohydrates commonly encountered in a biorefinery backdrop during the biochemical conversion of lignocellulosic biomass to biofuels/biochemicals. Here, we systematically compare and validate findings from four leading analytical approaches for detection and quantification of lignocellulosic biomass derived soluble carbohydrates. We compare these assay methods based on the overall ease of use, detection accuracy/sensitivity, commercial availability, analytical cost per assay run, and suitability for use by instructors in biorefining specific hands-on activity protocols. Next, we provide a detailed instructional protocol that utilizes one of these validated soluble sugar assays as part of a ∼90 min hands-on bioenergy focused activity (called ‘Grass-to-Gas!’) conducted at Rutgers University with pre-university high school students. ‘Grass-to-Gas!’ activity involves students running biochemical assays that helps them understand the various facets of cellulosic biomass hydrolysis by commercial cellulase enzymes and monitoring the total glucose product released using our validated sugar assays to finally estimate the fractional conversion of cellulose-to-glucose. Lastly, we further demonstrate how such carbohydrate-based analytical methods can be used by instructors to help university students explore and understand various chemistry, biochemistry, and chemical engineering concepts relevant to other advanced operations involved in lignocellulose biorefining. These activity protocols would greatly aid educators teaching interdisciplinary science and engineering concepts to students in the backdrop of lignocellulose biorefining.Competing Interest StatementThe authors have declared no competing interest.View Full Text

scientific communication and education↗

bioRxiv2020

Multiscale Characterization of Complex Binding Interactions of Cellulolytic Enzymes Highlights Limitations of Classical Approaches

Cellulolytic microorganisms, like Trichoderma reesei or Clostridium thermocellum, frequently have non-catalytic carbohydrate-binding modules (CBMs) associated with secreted or cell surface bound multidomain carbohydrate-active enzymes (CAZymes) like cellulases. Mostly type-A family CBMs are known to promote cellulose deconstruction by increasing the substrate-bound concentration of cognate cellulase catalytic domains. However, due to the interfacial nature of cellulose hydrolysis and the structural heterogeneity of cellulose, it has been challenging to fully understand the role of CBMs on cellulase activity using classical protein-ligand binding assays. Here, we report a single-molecule CAZyme assay for an industrially relevant processive cellulase Cel7A (from T. reesei) to reveal how subtle CBM1 binding differences can drastically impact cellulase motility/velocity and commitment to initial processive motion for deconstruction of two well-studied crystalline cellulose allomorphs (namely cellulose I and III). We take a multifaceted approach to characterize the complex binding interactions of all major type-A family representative CBMs including CBM1, using an optical-tweezers based single-molecule CBM-cellulose bond rupture assay to complement several classical bulk ensemble protein-ligand binding characterization methods. While our work provides a basis for the cautious use of Langmuir-type adsorption models to characterize classical protein-ligand binding assay data, we highlight the critical limitations of using such overly simplistic models to gain a truly molecular-level understanding of interfacial protein binding interactions at heterogeneous solid-liquid interfaces. Finally, molecular dynamics simulations provided a theoretical basis for the complex binding behavior seen for CBM1 towards two distinct cellulose allomorphs reconciling experimental findings from multiscale analytical methods. Significance StatementMultimodal biomolecular binding interactions involving carbohydrate polymers (e.g., cellulose, starch, chitin, glycosaminoglycans) are fundamental molecular processes relevant to the recognition, biosynthesis, and degradation of all major terrestrial and aquatic biomass. Protein-carbohydrate binding interactions are also critical to industrial biotechnology operations such as enzymatically-catalyzed bioconversion of starch and lignocellulose into biochemicals like ethanol. However, despite the ubiquitous importance of such interfacial processes, we have a poor molecular-level understanding of protein-polysaccharide binding interactions. Here, we provide a comprehensive experimental and theoretical analysis of bulk ensemble versus single-molecule binding interactions of enzyme motors and associated non-catalytic binding domains with cellulosic polysaccharides to highlight the critical limitations of applying classical biochemical assay techniques alone to understanding protein adsorption or biological activity at solid-liquid interfaces.

biochemistry↗

bioRxiv2020

Carbohydrate binding domains facilitate efficient oligosaccharides synthesis by enhancing mutant catalytic domain transglycosylation activity

Chemoenzymatic approaches using carbohydrate-active enzymes (CAZymes) offer a promising avenue for synthesis of glycans like oligosaccharides. Here, we report a novel chemoenzymatic route for cellodextrins synthesis employed by chimeric CAZymes, akin to native glycosyltransferases, involving the unprecedented participation of a non-catalytic lectin-like or carbohydrate-binding domains (CBMs) in the catalytic step for glycosidic bond synthesis using {beta}-cellobiosyl donor sugars as activated substrates. CBMs are often thought to play a passive substrate targeting role in enzymatic glycosylation reactions mostly via overcoming substrate diffusion limitations for tethered catalytic domains (CDs) but are not known to participate directly in any nucleophilic substitution mechanisms that impact the actual glycosyl transfer step. Our study provides evidence for the direct participation of CBMs in the catalytic reaction step for {beta}-glucan glycosidic bonds synthesis enhancing activity for CBM-based CAZyme chimeras by >140-fold over CDs alone. Dynamic intra-domain interactions that facilitate this poorly understood reaction mechanism were further revealed by small-angle X-ray scattering structural analysis along with detailed mutagenesis studies to shed light on our current limited understanding of similar transglycosylation-type reaction mechanisms. In summary, our study provides a novel strategy for engineering similar CBM-based CAZyme chimeras for synthesis of bespoke oligosaccharides using simple activated sugar monomers.

biochemistry↗

bioRxiv2020

Click-chemistry enabled directed evolution of glycosynthases for bespoke glycans synthesis

Engineering of carbohydrate-active enzymes like glycosynthases for chemoenzymatic synthesis of bespoke oligosaccharides has been limited by the lack of suitable directed evolution based protein engineering methods. Currently there are no ultrahigh-throughput screening methods available for rapid and highly sensitive single cell-based screening of evolved glycosynthase enzymes employing azido sugars as substrates. Here, we report a fluorescence-based approach employing click-chemistry for the selective detection of glycosyl azides (versus free inorganic azides) that facilitated ultrahigh-throughput in-vivo single cell-based assay of glycosynthase activity. This discovery has led to the development of a directed evolution methodology for screening and sorting glycosynthase mutants for synthesis of desired fucosylated oligosaccharides. Our screening technique facilitated rapid fluorescence activated cell sorting of a large library of glycosynthase variants (>106 mutants) expressed in E. coli to identify several novel mutants with increased activity for {beta}-fucosyl-azide activated donor sugars towards desired acceptor sugars, demonstrating the broader applicability of this methodology.

biochemistry↗