Biology subjects

Bandi, C. K.

Publications and source records attributed to Bandi, C. K..

5 recordsLinked to original sources

bioRxiv2026

Chemical Rescue Serves as a Predictive Proxy for Glycosynthase Activity on Glycosidic Bonds via a Shared Glycosyl Oxocarbenium Transition State

Engineered glycosynthases (GSs) are powerful biocatalysts for custom glycan synthesis, yet their optimization via directed evolution is severely constrained by bottlenecks in high-throughput screening for activated azido-sugar donors. Here, we demonstrate that chemical rescue (CR)--the azide-mediated restoration of hydrolytic activity in nucleophile-deficient mutants--serves as a predictive, high-throughput proxy for glycosynthase activity. Applying an azide-responsive Escherichia coli biosensor screen to a site-saturation mutagenesis library of Thermotoga maritima -L-fucosidase (TmAfc), we established a strong rank-order correlation between CR and GS activities in both crude lysates ({rho} = 0.73) and purified enzymes ({rho} = 0.95). Transition path sampling and QM/MM umbrella sampling revealed that both pathways proceed through a shared oxocarbenium-ion-like transition state ({Delta}G{ddagger} {approx} 8.7 kcal/mol), providing a structural and thermodynamic rationale for using CR to select for transition-state-stabilizing mutations. Biochemical characterization of top-performing variants yielded an engineered fucosynthase (TmAfc_D224G_N70D_T392S) exhibiting a nearly 100-fold enhancement in Vmax alongside altered regioselectivity. This two-tiered screening framework leverages cost-effective chemical rescue assays to streamline glycosynthase engineering for tailored glycans synthesis.

biochemistry↗

bioRxiv2026

Topological reprogramming transforms an integral membrane oligosaccharyltransferase into a water-soluble glycosylation catalyst

Glycosyltransferases (GTs) catalyze the formation of new glycosidic bonds and thus are vital for synthesizing natures vast repertoire of glycans and glycoconjugates and for engineering glycan-related medicines and materials. However, obtaining detailed structural and functional insights for the >750,000 known GTs is limited by difficulties associated with their efficient recombinant expression. Members of the GT-C fold, in particular, pose the most significant expression challenges due to the integration and folding requirements of their multiple membrane-spanning regions. Here, we address this challenge by engineering water-soluble variants of an archetypal GT-C fold enzyme, namely the oligosaccharyltransferase PglB from Campylobacter jejuni (CjPglB), which possesses 13 hydrophobic transmembrane helices. To render CjPglB water-soluble, we leveraged two advanced protein engineering methods: one that is universal called SIMPLEx (solubilization of IMPs with high levels of expression) and the other that is custom tailored called WRAPs (water-soluble RFdiffused amphipathic proteins). Each approach was able to transform CjPglB into a water-soluble enzyme that could be readily expressed in the cytoplasm of Escherichia coli cells at yields in the 3-6 mg/L range. Importantly, solubilization was achieved without the need for detergents and with retention of catalytic function. Collectively, our findings demonstrate that both SIMPLEx and WRAPs are promising platforms for advancing the molecular characterization of even the most structurally complex GTs, while also enabling broader GT-mediated glycosylation capabilities within synthetic glycobiology applications.

synthetic biology↗

bioRxiv2022

Machine learning assisted ligand binding energy prediction for in silico generated glycosyl hydrolase enzyme combinatorial mutant library

Molecular docking is a computational method used to predict the preferred binding orientation of one molecule to another when bound to each other to form an energetically stable complex. This approach has been widely used for early-stage small-molecule drug design as well as identifying suitable protein-based macromolecule residues for mutagenesis. Estimating binding free energy, based on docking interactions of protein to its ligand based on an appropriate scoring function is often critical for protein mutagenesis studies to improve the activity or alter the specificity of targeted enzymes. However, calculating docking free energy for a large number of protein mutants is computationally challenging and time-consuming. Here, we showcase an end-to-end computational workflow for predicting the binding energy of pNP-Xylose substrate docked within the substrate binding site for a large library of combinatorial mutants of an alpha-L-fucosidase (TmAfc, PDB ID-2ZWY) belonging to Thermotoga maritima glycosyl hydrolase (GH) family 29. Briefly, in silico combinatorial mutagenesis was performed for the top conserved residues in TmAfc as determined by running multiple sequence alignment against all GH29 family enzyme sequences downloaded from an in-house developed Carbohydrate-Active enZyme (CAZy) database retriever program. The binding energy was calculated through Autodock Vina with pNP-Xylose ligand docking with energy minimized TmAfc mutants, and the data was then used to train a neural network model which was also validated for model predictions using data from Autodock Vina. The current workflow can be adopted for any family of CAZymes to rapidly identify the effect of different mutations within the active site on substrate binding free energy to identify suitable targets for mutagenesis. We anticipate that this workflow could also serve as the starting point for performing more sophisticated and computationally intensive binding free energy calculations to identify targets for mutagenesis and hence optimize use of wet lab resources.

bioengineering↗

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↗