Antiviral drug recognition and elevator-type transport motions of CNT3.

Nucleoside analogs have broad clinical utility as antiviral drugs. Key to their systemic distribution and cellular entry are human nucleoside transporters. Here, we establish that the human concentrative nucleoside transporter 3 (CNT3) interacts with antiviral drugs used in the treatment of coronavirus infections. We report high-resolution single-particle cryo-electron microscopy structures of bovine CNT3 complexed with antiviral nucleosides N4-hydroxycytidine, PSI-6206, GS-441524 and ribavirin, all in inward-facing states. Notably, we found that the orally bioavailable antiviral molnupiravir arrests CNT3 in four distinct conformations, allowing us to capture cryo-electron microscopy structures of drug-loaded outward-facing and drug-loaded intermediate states. Our studies uncover the conformational trajectory of CNT3 during membrane transport of a nucleoside analog antiviral drug, yield new insights into the role of interactions between the transport and the scaffold domains in elevator-like domain movements during drug translocation, and provide insights into the design of nucleoside analog antiviral prodrugs with improved oral bioavailability.

Genetically Engineered Nanoparticles of Asymmetric Triblock Polypeptide with a Platinum(IV) Cargo Outperforms a Platinum(II) Analog and Free Drug in a Murine Cancer Model.

The development of platinum(Pt)-drugs for cancer therapy has stalled, as no new Pt-drugs have been approved in over a decade. Packaging small molecule drugs into nanoparticles is a way to enhance their therapeutic efficacy. To date, there has been no direct comparison of relative merits of the choice of Pt oxidation state in the same nanoparticle system that would allow its optimal design. To address this lacuna, we designed a recombinant asymmetric triblock polypeptide (ATBP) that self-assembles into rod-shaped micelles and chelates Pt(II) or enables covalent conjugation of Pt(IV) with similar morphology and stability. Both ATBP-Pt(II) and ATBP-Pt(IV) nanoparticles enhanced the half-life of Pt by ∼45-fold, but ATBP-Pt(IV) had superior tumor regression efficacy compared to ATBP-Pt(II) and cisplatin. These results suggest loading Pt(IV) into genetically engineered nanoparticles may yield a new generation of more effective platinum-drug nanoformulations.

Molecular organization and protein stability of the Clostridium thermocellum glucuronoxylan endo-ß-1,4-xylanase of family 30 glycoside hydrolase in solution.

Glucuronoxylan-ß-1,4-xylanohydrolase from Clostridium thermocellum (CtXynGH30) hydrolyzes ß-1,4-xylosidic linkages in 4-O-Methyl-D-glucuronoxylan. CtXynGH30 comprises an N-terminal catalytic domain, CtXyn30A, joined by a typical linker sequence to a family 6 carbohydrate-binding module, termed CtCBM6. ITC, mass spectrometric and enzyme activity analyses of CtXyn30A:CtCBM6 (1:1 M ratio), CtXyn30A and CtXynGH30 showed that the linker peptide plays a key role in connecting and orienting CtXyn30A and CtCBM6 modules resulting in the enhanced activity of CtXynGH30. To visualize the disposition of the two protein domains of CtXynGH30, SAXS analysis revealed that CtXynGH30 is monomeric and has a boot-shaped molecular envelope in solution with a Dmax of 18 nm and Rg of 3.6 nm. Kratky plot displayed the protein in a fully folded and flexible state. The ab initio derived dummy atom model of CtXynGH30 superposed well with the modelled structure.

Improving the Performance of Tao-Mo Non-empirical Density Functional with Broader Applicability in Quantum Chemistry and Materials Science.

A revised version of the semilocal exchange-correlation functional [Tao, J.; Mo, Y. Phys. Rev. Lett. 2016, 117, 073001] (TM) is proposed by incorporating the modifications to its correlation content obtained from the full high-density second-order gradient expansion as proposed in the case of the revised Tao-Perdew-Staroverov-Scuseria (revTPSS) [Perdew, J. P.; Ruzsinszky, A.; Csonka, G. I.; Constantin, L. A.; Sun, J. Phys. Rev. Lett. 2009, 103, 026403] functional. The present construction improves the performance of the TM functional over a wide range of quantum chemical and solid-state properties (thermochemical and structural). More specifically, the cohesive energies, jellium surface exchange-correlation energies, and real metallic surface energies are improved by preserving the accuracy of the solid-state lattice constants and bulk moduli. The present proposition is not only physically motivated but also enhances the applicability of the TM functional. New physical insights with the proper exemplification of the present modification, which is presented here, can further help in constructing more realistic non-empirical density functionals.

The multi-ligand binding first family 35 Carbohydrate Binding Module (CBM35) of Clostridium thermocellum targets rhamnogalacturonan I.

Carbohydrate Binding Modules (CBMs) targeting cellulose, xylan and mannan have been reported, however, a CBM targeting rhamnogalacturonan I (RG I) has never been identified. We had studied earlier a rhamnogalacturonan lyase (CtRGL) from Clostridium thermocellum that was associated with a family 35 CBM, Rgl-CBM35. In this study we show that Rgl-CBM35 displays binding with ß-d-glucuronic acid (ß-D-GlcpA), Δ4,5-anhydro-d-galactopyranosyluronic acid (Δ4,5-GalpA), rhamnogalacturonan I, arabinan, galactan, glucuronoxylans and arabinoxylans. Rgl-CBM35 contains a conserved ligand binding site in the loops known for binding ß-D-GlcpA and Δ4,5-GalpA moiety of unsaturated RG I and pectic-oligosaccharides. Mutagenesis revealed that Asn118 plays an important role in binding ß-D-GlcpA, Δ4,5-GalpA, sugarbeet arabinan and potato galactan at its conserved ligand binding site present in surface exposed loops. EDTA-treated Rgl-CBM35 showed no affinity towards ß-D-GlcpA and Δ4,5-GalpA underscoring Ca2+ mediated ligand recognition. Contrastingly, the EDTA-treated Rgl-CBM35 and its mutant N118A displayed affinity for sugarbeet arabinan and potato galactan. The curtailed affinity of Y37A/N118A and R69A/N118A double mutants towards sugarbeet arabinan emphasized the presence of a second ligand binding site. Rgl-CBM35 is the first CBM reported to primarily target RG I and also is the first member of family 35 CBM possessing at least two ligand binding sites.

SAXS and homology modelling based structure characterization of pectin methylesterase a family 8 carbohydrate esterase from Clostridium thermocellum ATCC 27405.

Pectin methylesterase (CtPME) from Clostridium thermocellum of family 8 carbohydrate esterase (CE8) belongs to pectin methylesterase super family (E.C.3.1.1.11). BLAST analysis of CtPME showed 38% sequence identity with PME from Erwinia chrysanthemi. Multiple sequence alignment of CtPME with other known structures of pectin methylesterase revealed the conserved and semi-conserved amino acid residues. Homology modelling of CtPME structure revealed a characteristic right handed parallel ß-helices. The energy of modelled structure was minimized by using YASARA software. The Ramachandran plot of CtPME shows 83.7% residues in non-glycine and non-proline residues in most-favorable region, 13.8% in additional allowed region and 1.4% in generously allowed region, indicating that CtPME has a stable conformation. The secondary structure of CtPME predicted using PSI-Pred software and confirmed by the circular dichroism (CD) showed α-helices (3.1%), ß-sheets (40.1%) and random coils (56.9%). Small Angle X-ray Scattering (SAXS) analysis demonstrated the overall shape and structural characterization of CtPME in solution form. Guinier analysis gave the radius of gyration (Rg) 2.28 nm for globular shape and 0.74 nm for rod shape. Kratky plot gave the indication that protein is fully folded in solution. The ab initio derived dummy atom model of CtPME superposed well on modelled CtPME structure.

Assessing the performance of the recent meta-GGA density functionals for describing the lattice constants, bulk moduli, and cohesive energies of alkali, alkaline-earth, and transition metals.

The bulk properties such as lattice constants, bulk moduli, and cohesive energies of alkali, alkaline-earth, and transition metals are studied within the framework of the recently developed meta-GGA (meta-Generalized Gradient Approximation) level semilocal exchange-correlation functionals. To establish the applicability, broadness, and accuracy of meta-GGA functionals, we also put the results obtained using PBE (Perdew-Burke-Ernzerhof) [J. P. Perdew et al., Phys. Rev. Lett. 77, 3865 (1996)] and PBE reparameterized for solid [J. P. Perdew et al., Phys. Rev. Lett. 100, 136406 (2008)] GGA functionals. The interesting feature of the present paper is that it measures the accuracy of the recently developed TM (Tao-Mo), TMTPSS [TM exchange with Tao-Perdew-Staroverov-Scuseria (TPSS)] [J. Tao and Y. Mo, Phys. Rev. Lett. 117, 073001 (2016)] correlation, and strongly constrained and appropriately normed [J. Sun et al., Phys. Rev. Lett. 115, 036402 (2015)] functionals to calculate the aforementioned properties. Not only that, we also include other (popular) meta-GGA functionals in order to have a closer look at the performance of the meta-GGA functionals too. The present systematic investigation shows that the TM functional is accurate in describing the lattice constants while for cohesive energies and bulk moduli, the PBE and modified TPSS perform better compared to others.

Comparative analysis of pretreatment methods on sorghum (Sorghum durra) stalk agrowaste for holocellulose content.

This study compares different types of pretreatment methods, such as thermal pretreatment at 120 °C, autoclaving, microwaving and ultrasonication in the presence of water, dilute acid (1% H2SO4) or dilute alkali (1% NaOH) on Sorghum stalk with respect to the holocellulose and Acid Detergent/Insoluble Lignin content. Among all the methods, pretreatment with 1% NaOH along with autoclaving at 121 °C and 15 psi for 30 min was the most effective method for Sorghum stalk. Fourier Transform Infra-Red spectroscopy analysis of this pretreated biomass showed the removal of lignin and Field Emission Scanning Electron Microscope analysis displayed enhanced surface roughness. The enzymatic hydrolysis of raw and best pretreated Sorghum stalk using recombinant endo-ß-1,4-glucanase (CtCel8A) and ß-1,4-glucosidase (CtBgl1A) both from Clostridium thermocellum gave glucose yields, 22.4 mg/g raw biomass and 34 mg/g pretreated biomass, respectively, resulting in 1.5-fold increase of glucose yield after the pretreatment.

Computational and SAXS-based structure insights of pectin acetyl esterase (CtPae12B) of family 12 carbohydrate esterase from Clostridium thermocellum ATCC 27405.

Pectin is a complex form of polysaccharide and is composed of several structural components that require the concerted action of several pectinases for its complete degradation. In this study, in silico and solution structure of a pectin acetyl esterase (CtPae12B) of family 12 carbohydrate esterase (CE12) from Clostridium thermocellum was determined. The CtPae12B modelled structure, showed a new α/ß hydrolase fold, similar to the fold found in the crystal structures of its nearest homologues from CE12 family, which differed from α/ß hydrolase fold found in glycoside hydrolases. In the active site of CtPae12B, two loops (loop1 and loop6) play an important role in the formation of a catalytic triad Ser15-Asp187-His190, where Ser15 acts as a nucleophile. The structural stability of CtPae12B and its catalytic site was detected by performing molecular dynamic (MD) simulation which showed stable and compact conformation of the structure. Molecular docking method was employed to analyse the conformations of various suitable ligands docked at the active site of CtPae12B. The stability and structural specificity of the catalytic residues with the ligand, 4-nitrophenyl acetate (4-NPA) was confirmed by MD simulation of CtPae12B-4NPA docked complex. Moreover, it was found that the nucleophile Ser15, forms hydrophobic interaction with 4-NPA in the active site to complete covalent catalysis. Small angle X-ray scattering analysis of CtPae12B at 3 mg/mL displayed elongated, compact and monodispersed nature in solution. The ab initio derived dummy model showed that CtPae12B exists as a homotrimer at 3 mg/mL which was also confirmed by dynamic light scattering.Communicated by Ramaswamy H. Sarma.

Preparation of Nucleosome Core Particles Complexed with DNA Repair Factors for Cryo-Electron Microscopy Structural Determination.

DNA repair in the context of chromatin is poorly understood. Biochemical studies using nucleosome core particles, the fundamental repeating unit of chromatin, show most DNA repair enzymes remove DNA damage at reduced rates as compared to free DNA. The molecular details on how base excision repair (BER) enzymes recognize and remove DNA damage in nucleosomes have not been elucidated. However, biochemical BER data of nucleosomal substrates suggest the nucleosome presents different structural barriers dependent on the location of the DNA lesion and the enzyme. This indicates the mechanisms employed by these enzymes to remove DNA damage in free DNA may be different than those employed in nucleosomes. Given that the majority of genomic DNA is assembled into nucleosomes, structural information of these complexes is needed. To date, the scientific community lacks detailed protocols to perform technically feasible structural studies of these complexes. Here, we provide two methods to prepare a complex of two genetically fused BER enzymes (Polymerase ß and AP Endonuclease1) bound to a single-nucleotide gap near the entry-exit of the nucleosome for cryo-electron microscopy (cryo-EM) structural determination. Both methods of sample preparation are compatible for vitrifying quality grids via plunge freezing. This protocol can be used as a starting point to prepare other nucleosomal complexes with different BER factors, pioneer transcription factors, and chromatin-modifying enzymes.

A humanized nanobody phage display library yields potent binders of SARS CoV-2 spike.

Neutralizing antibodies targeting the SARS-CoV-2 spike protein have shown a great preventative/therapeutic potential. Here, we report a rapid and efficient strategy for the development and design of SARS-CoV-2 neutralizing humanized nanobody constructs with sub-nanomolar affinities and nanomolar potencies. CryoEM-based structural analysis of the nanobodies in complex with spike revealed two distinct binding modes. The most potent nanobody, RBD-1-2G(NCATS-BL8125), tolerates the N501Y RBD mutation and remains capable of neutralizing the B.1.1.7 (Alpha) variant. Molecular dynamics simulations provide a structural basis for understanding the neutralization process of nanobodies exclusively focused on the spike-ACE2 interface with and without the N501Y mutation on RBD. A primary human airway air-lung interface (ALI) ex vivo model showed that RBD-1-2G-Fc antibody treatment was effective at reducing viral burden following WA1 and B.1.1.7 SARS-CoV-2 infections. Therefore, this presented strategy will serve as a tool to mitigate the threat of emerging SARS-CoV-2 variants.

Computational modeling and small-angle X-ray scattering based structure analysis and identifying ligand cleavage mechanism by processive endocellulase of family 9 glycoside hydrolase (HtGH9) from Hungateiclostridium thermocellum ATCC 27405.

The cellulases of family 9 glycoside hydrolase with subtle difference in amino acid sequence have shown different types of catalytic activities such as endo-, exo- or processive endocellulase. However, the reason behind the different types of catalytic activities still unclear. In this study, the processive endocellulase, HtGH9 of family 9 GH from Hungateiclostridium thermocellum was modeled by homology modeling. The catalytic module (HtGH9t) of HtGH9 modeled structure displayed the (α/α)6 barrel topology and associated family 3 carbohydrate binding module (HtCBM3c) displayed ß-sandwich fold. Ramachandran plot of HtGH9 modeled structure displayed all the amino acid residues in allowed region except Asn225 and Asp317. Secondary structure analysis of modeled HtGH9 showed the presence of 41.3% α-helices and 11.0% ß-strands which was validated through circular dichroism analysis that showed the presence of 42.6% α-helices and 14.5% ß-strands. Molecular Dynamic (MD) simulation of HtGH9 structure for 50 ns showed Root Mean Square Deviation (RMSD), 0.84 nm and radius of gyration (Rg) 3.1 nm. The Small-angle X-ray scattering of HtGH9 confirmed the monodisperse state. The radius of gyration for globular shape (Rg) was 5.50 ± 0.15 nm and for rod shape (Rc) by Guinier plot was 2.0 nm. The loop formed by amino acid residues, 264-276 towards one end of the catalytic site of HtGH9 forms a barrier, that blocks the non-reducing end of the cellulose chain causing the processive cleavage resulting in the release of cellotetraose. The position of the corresponding loop in cellulases of family 9 GH is responsible for different types of cleavage patterns.

Small angle X-ray scattering based structure, modeling and molecular dynamics analyses of family 43 glycoside hydrolase α-L-arabinofuranosidase from Clostridium thermocellum.

Enzymes that participate in the hydrolysis of complex carbohydrates display a modular architecture, although the significance of enzyme modularity to flexibility and catalytic efficacy is not fully understood. α-L-arabinofuranosidase from Clostridium thermocellum (CtAraf43) catalyzes the release of α-1,2-, α-1,3-, or α-1,5- linked L-arabinose from arabinose decorated polysaccharides. CtAraf43 comprises an N-terminal catalytic domain (CtAbf43A) connected with two family 6 carbohydrate-binding modules (CBMs), termed as CtCBM6A and CtCBM6B, through flexible linker peptides. Here, we modeled the structure of CtAraf43 revealing that the module, CtAbf43A displays a 5-fold ß-propeller fold and the CBMs the typical jellyroll type ß-sandwich folds. Ramachandran plot showed 98.5% residues in the favored region and 1.5% residues in the disallowed region. Molecular dynamics simulation analysis of CtAraf43 revealed significant flexibility that is more expressive in the C-terminal CtCBM6B module in terms of structure and orientation. Small angle X-ray scattering analysis of CtAraf43 revealed its elongated structure. CtAraf43 at 1.2 mg/mL demonstrated the monomeric nature and a multi-modular shaped molecular envelope in solution with a Dmax of 12 nm. However, at 4.7 mg/mL, CtAraf43 displayed a dimeric structure and elongated molecular envelope. Kratky plot analysis revealed the folded state of CtAraf43 with limited flexibility at both concentrations. The data revealed higher flexibility at the C-terminal of CtAraf43 suggesting a coordinated action of the N-terminal catalytic module CtAbf43A and the internal CtCBM6A.AbbreviationCBMsCarbohydrate Binding ModulesCtAraf43α-L-arabinofuranosidaseGHsGlycoside HydrolasesMDMolecular DynamicsRMSDRoot Mean Square DeviationRMSFRoot Mean Square FluctuationSAXSSmall angle X-ray scatteringCommunicated by Ramaswamy H. Sarma.

Extraction and characterization of xylan from sugarcane tops as a potential commercial substrate.

Xylan is the major hemicellulose present in sugarcane stem secondary cell walls. Xylan is composed of xylose backbone with a high degree of substitutions, which affects its properties. In the present study, the xylan from sugarcane tops (SCT) was extracted and characterized. Compositional analysis of xylan extracted from SCT (SCTx) displayed the presence of 74% of d-xylose residues, 16% of d-glucuronic acid residues and 10% of l-arabinose. High performance size exclusion chromatographic analysis of SCTx displayed a single peak corresponding to a molecular mass of ∼57 kDa. The Fourier transform infrared spectroscopic analysis of SCTx displayed the peaks corresponding to those obtained from commercial xylan. FESEM analysis of SCTx showed the granular and porous surface structure. Differential thermogravimetric analysis (DTG) of SCTx displayed two thermal degradation temperatures (Td) of 228°C, due to breakdown of the side chains of glucuronic acid and arabinose and 275°C, due to breakdown of xylan back bone. The presence of arabinose and glucuronic acid as a side chains was confirmed by the DTG and thermogravimetric analysis. The CHNS analysis of SCTx showed the presence of only carbon and hydrogen supporting its purity. The recombinant xylanase (CtXyn11A) from Clostridium thermocellum displayed a specific activity of 1394 ± 51 U/mg with SCTx, which was higher than those with commercial xylans. The thin layer chromatography and electrospray ionization mass spectroscopy analyses of CtXyn11A hydrolysed SCTx contained a series of linear xylo-oligosaccharides ranging from degree of polymerization 2-6 and no substituted xylo-oligosaccharides because of the endolytic activity of enzyme. The extracted xylan from SCT can be used as an alternative commercial substrate and for oligo-saccharide production.

Computational guided drug repurposing for targeting 2'-O-ribose methyltransferase of SARS-CoV-2.

AIMS: The recent outbreak of pandemic severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) has led the world towards a global health emergency. Currently, no proper medicine or effective treatment strategies are available; therefore, repurposing of FDA approved drugs may play an important role in overcoming the situation. MATERIALS AND METHODS: The SARS-CoV-2 genome encodes for 2-O-methyltransferase (2'OMTase), which plays a key role in methylation of viral RNA for evading host immune system. In the present study, the protein sequence of 2'OMTase of SARS-CoV-2 was analyzed, and its structure was modeled by a comparative modeling approach and validated. The library of 3000 drugs was screened against the active site of 2'OMTase followed by re-docking analysis. The apo and ligand-bound 2'OMTase were further validated and analyzed by using molecular dynamics simulation. KEY FINDINGS: The modeled structure displayed the conserved characteristic fold of class I MTase family. The quality assessment analysis by SAVES server reveals that the modeled structure follows protein folding rules and of excellent quality. The docking analysis displayed that the active site of 2'OMTase accommodates an array of drugs, which includes alkaloids, antivirals, cardiac glycosides, anticancer, steroids, and other drugs. The redocking and MD simulation analysis of the best 5 FDA approved drugs reveals that these drugs form a stable conformation with the 2'OMTase. SIGNIFICANCE: The results suggested that these drugs may be used as potential inhibitors for 2'OMTase for combating the SARS-CoV-2 infection.

Structure and dynamics analysis of a family 43 glycoside hydrolase α-L-arabinofuranosidase (PsGH43_12) from Pseudopedobacter saltans by computational modeling and small-angle X-ray scattering.

The structure and molecular dynamics of α-L-arabinofuranosidase (PsGH43_12) of family 43 glycoside hydrolase, subfamily 12 from Pseudopedobacter saltans were studied. The modeled PsGH43_12 structure displayed 5-bladed ß-propeller fold at N-terminal and ß-sandwich fold at C terminal. Ramachandran plot showed 95.7% residues in favored and 3.3% in the generously allowed region and only 1% residues in the disallowed region. The secondary structure analysis of PsGH43_12 by circular dichroism revealed 2.7% α-helices, 30.33% ß-strands and 66.97% random coils. Protein melting study of PsGH43_12 showed complete unfolding at 65°C and did not require any metal ion for its stability. Molecular docking analysis confirmed the involvement of active site residues Asp71, Asp180 and Glu247 in the catalysis, which was also confirmed by the site-directed mutagenesis of these residues. SAXS analysis displayed that PsGH43_12 is monomeric and a fully folded state in solution form. Guinier analysis gave the radius of gyration (Rg) 2.8 ± 0.09 nm. The maximum dimension and Rg of PsGH43_12 estimated from P(R) plot were 9.7 nm and 2.81 nm, respectively. The ab initio derived dummy model of PsGH43_12 displayed a bell-like shape. The ab initio derived dummy model superposed well with its comparative modeled structure except the N-terminal His6-tag region.

Combined SAXS and computational approaches for structure determination and binding characteristics of Chimera (CtGH1-L1-CtGH5-F194A) generated by assembling ß-glucosidase (CtGH1) and a mutant endoglucanase (CtGH5-F194A) from Clostridium thermocellum.

Chimera (CtGH1-L1-CtGH5-F194A) developed by fusing ß-glucosidase (CtGH1) at N-terminal and endoglucanase (CtGH5-F194A) at C-terminal was structurally characterized. Its secondary structure analysis by CD showed 38% α-helix, 9.3% ß-sheets and 52.7% random coils corroborating with prediction. In-silico modeled structure of Chimera comprised two modules, CtGH1 and CtGH5-F194A displaying (α/ß)8 fold. Ramachandran plot of Chimera showed 99.9% residues in allowed region. Binding interaction of Chimera with cello-oligosaccharides suggested active forms of CtGH1 and CtGH5-F194A and their involvement in catalysis. MD simulation of cellohexaose bound endoglucanase module of Chimera showed favourable flexibility in loops, LA with H-bond formation with Asn510 and in loop LC relocation of Tyr687 away from active site efficiently releasing the product after catalysis. Higher short range interaction energy of Chimera, -383 kJ/mol than the individual endoglucanase, 254 kJ/mol against cellohexaose suggested higher efficient catalysis by Chimera. ß-Glucosidase module of Chimera showed fluctuations in outer loops suggesting conformational changes that might be contributing to improved hydrolysis. SAXS analysis of Chimera displayed monodispersed state. Guinier analysis of Chimera showed globular shape (Rg= 3.15 ± 0.10 nm). Kratky plot confirmed fully folded and flexible behaviour in solution. Gasbor modeled structure of Chimera displayed an elongated structure with two modules having shape similar to bean-bag contour.

Structure and dynamics analysis of a new member heparinase II/III of family 12 polysaccharide lyase from Pseudopedobacter saltans by computational modeling and small-angle X-ray scattering.

The structure of heparinase II/III belonging to family 12 polysaccharide lyase (PsPL12a) from Pseudopedobacter saltans was generated by homology modeling. Multiple sequence alignment showed conserved (Asn216, Tyr270 and His400) and semi-conserved active site amino acid residues. The modeled structure of PsPL12a displayed α/α toroid domain at N-terminal and antiparallel ß sheets at C-terminal domain. The modeled structure was similar to those of heparinases from polysaccharide lyase 12 and 21 families. Validation of PsPL12a model by Ramachandran plot showed 94.6% of residues in the favored region, 5.2% of residues in the allowed region and only 0.2% of residues in the outlier region. The area and volume computed for PsPL12a displayed nearly a closed conformation of the active site, similar to HepIII from Bacteroides thetaiotaomicron. The charge calculation on the surface of the PsPL12a structure showed the higher distribution of positive charge in the active site cleft as compared with other homologous structures. Molecular docking study of MD-simulated PsPL12a structure with heparin oligosaccharide showed high binding affinity as compared with heparan sulfate oligosaccharides. Comparison of the active site of modeled PsPL12a with other homologous heparinases revealed putative catalytic triad involving the residues Asn216, His400 and Tyr270. Small-angle X-ray scattering analysis of PsPL12a displayed a fully folded and boxing glove-like envelop.Communicated by Ramaswamy H. Sarma.

Small-angle X-ray scattering based structure, modeling and molecular dynamics analyses of a family 5 glycoside hydrolase first endo-mannanase named as RfGH5_7 from Ruminococcus flavefaciens.

Endo-ß-1,4-mannanase named as RfGH5_7 from Ruminococcus flavefaciens cloned, expressed and purified earlier was structurally characterized in present study. The RaptorX modeled structure of RfGH5_7 showed a (ß/α)8 Triose-phosphate Isomerase (TIM) barrel fold. The Ramachandran plot assessment of RfGH5_7 showed that all amino acids fall in allowed region except one, Asn22 in the disallowed region. The superposition of RfGH5_7 modeled structure with its nearest homologues revealed that Glu154 acts as proton donor while Glu249 acts as nucleophile. Secondary structure of RfGH5_7 through Circular Dichroism (CD) analysis revealed 33.5% α-helices, 17% ß-strands and 49.5% random coils. Molecular Dynamic (MD) simulation showed Root Mean Square Deviation (RMSD), 0.67 nm and radius of gyration (Rg) between 1.9 nm and 1.85 nm. The binding interaction of mannotetraose on the surface of RfGH5_7 structure displayed polar interactions with His219, Tyr221, Trp278, Ser279 and Gly282 residues. Small-angle X-ray scattering (SAXS) analysis displayed the intact and monodispersed nature of the enzyme RfGH5_7. The radius of gyration (Rg) by Guinier analysis for globular shape was found to be 2.29 ± 0.09 nm and for rod-shape it was 0.95 ± 0.02 nm. Kratky plot confirmed that RfGH5_7 structure is compact and folded in solution. The ab initio derived dummy model of RfGH5_7 displayed single domain structure of yellow humped fish like shape. The RfGH5_7 modeled structure was well fitted with ab initio derived model from SAXS data. Communicated by Ramaswamy H. Sarma.

Molecular Characterization, Regioselective and Synergistic Action of First Recombinant Type III α-L-arabinofuranosidase of Family 43 Glycoside Hydrolase (PsGH43_12) from Pseudopedobacter saltans.

α-L-Arabinofuranosidase (PsGH43_12) of family 43 glycoside hydrolase and subfamily 12 from Pseudopedobacter saltans was cloned, over-expressed and biochemically characterized. PsGH43_12 displayed molecular mass, ~ 65 kDa. It exhibited activity in pH (5-9) and temperature range (35-55 °C) with maxima at pH 6.5 and 50 °C. PsGH43_12 gave 88.7 U/mg specific activity against rye arabinoxylan and 78.9 U/mg against wheat arabinoxylan. PsGH43_12 displayed Km and Vmax, 3.02 mg/ml and 103 µmole/min/mg, respectively, against rye arabinoxylan and 2.17 mM and 100.7 µmole/min/mg, respectively, against pNP-α-L-arabinofuranoside. 10 mM Mg2+ or Ca2+ ions enhanced PsGH43_12 activity by 54% or 33%, respectively. PsGH43_12 hydrolyzed rye arabinoxylan and released only L-arabinosyl moiety as main product, confirming its specificity towards α-L-arabinofuranoside. The regioselective analysis by NMR showed that PsGH43_12 belongs to type III α-L-arabinofuranoside. The synergistic behavior of PsGH43_12 in saccharification of mild alkali pretreated finger miller stalk (FMS) along with xylanase (CtXyn11A) from Clostridium thermocellum and xylosidase (BoGH43) from Bacteroides ovatus gave twofold higher total reducing sugar (TRS) yield. TLC analysis of pretreated FMS hydrolysed by CtXyn11A and BoGH43 showed xylooligosaccharides and xylose. Addition of PsGH43_12 to above combination gave mostly xylose and arabinose confirming their synergistic behavior and displaying their applicability in hydrolysis of hemicellulosic biomass.