@article { ISI:000237440200012, title = {Structural and active site modification studies implicate Glu, Trp and Arg in the activity of xylanase from alkalophilic Bacillus sp (NCL 87-6-10)}, journal = {Enzyme and Microbial Technology}, volume = {39}, number = {1}, year = {2006}, month = {JUN}, pages = {67-73}, publisher = {ELSEVIER SCIENCE INC}, type = {Article}, address = {360 PARK AVE SOUTH, NEW YORK, NY 10010-1710 USA}, abstract = {

Structural studies and residue modification using group specific reagents were used to ascertain the role of different functional groups in xylanase from alkalophilic Bacillus sp. (NCL 87-6-10). Treatment with N-bromosuccinimide resulted in fast enzyme inactivation. Reaction with Woodward{\textquoteright}s reagent K resulted in initial fast followed by slower inactivation. In both cases enzyme was protected against inactivation by the substrate, xylan. The reaction of the enzyme with phenylglyoxal has revealed one essential arginine residue at the active site. The three-dimensional structural analysis of the xylanase at 2.8 angstrom resolution also implicates involvement of Trp, and Arg residues and carboxylate groups in the binding of substrate and in the catalysis of xylanase. (c) 2005 Published by Elsevier Inc.

}, keywords = {active-site residues, alkaline xylanase, Chemical modification, three-dimensional structure}, issn = {0141-0229}, doi = {10.1016/j.enzmictec.2005.09.010}, author = {Balakrishnan, H. and Satyanarayana, L. and Gaikwad, S. M. and Suresh, C. G.} } @article { ISI:000245519000047, title = {Active site directed chemical modification of alpha-galactosidase from bacillus stearothermophilus (NCIM 5146): involvement of lysine, tryptophan and carboxylate residues in catalytic site}, journal = {Enzyme and Microbial Technology}, volume = {40}, number = {5}, year = {2007}, month = {APR}, pages = {1312-1320}, publisher = {ELSEVIER SCIENCE INC}, type = {Article}, address = {360 PARK AVE SOUTH, NEW YORK, NY 10010-1710 USA}, abstract = {

The catalytic amino acid residues of the extracellular a-galactosidase (alpha-D-galactoside galactohydrolase; EC 3.2.1.22) from Bacillus stearothermophilus NCIM 5146 were investigated by pH dependence and chemical modification studies. These results suggested that carboxylate and a lysine residue take part in catalysis and only lysine residues were essential for substrate binding. Carbodiimide mediated chemical modification of the enzyme also supported that a carboxylate residue located in the active site act as a nucleophile base in substrate cleavage. Acylation and reductive methylation of lysine residues by acetic, citraconic anhydride and sodium borohydride suggested that four protonated lysine residues carrying positive charge on its epsilon-amino group provides the positive charge density for binding of the substrate. Additionally four tryptophan residues also found near to the active site and in a moderately hydrophobic environment. Kinetic and thermal inactivation study of modified enzyme indicated that these tryptophan residues might have a role in the catalytic site as well as in the thermal stabilization of active site conformation at higher temperature. (c) 2006 Elsevier Inc. All rights reserved.

}, keywords = {Active site, alpha-galactosidase, Bacillus stearothermophilus, carboxylate, Chemical modification, lysine, Tryptophan}, issn = {0141-0229}, doi = {10.1016/j.enzmictec.2006.10.004}, author = {Gote, M. M. and Khan, Mohammad Islam and Khire, Jayant Malhar} } @article { ISI:000272134300006, title = {Interaction of alpha-mannosidase from aspergillus fischeri with glycosidase inhibitors, metal ions and group specific reagents}, journal = {Research Journal of Biotechnology}, volume = {4}, number = {4}, year = {2009}, month = {NOV}, pages = {39-48}, publisher = {RESEARCH JOURNAL BIOTECHNOLOGY}, address = {SECTOR A-80, SCHEME NO 54, VIJAY NAGAR, A B ROAD, INDORE, 452 010 MP, INDIA}, abstract = {

As an initial step towards using alpha-mannosidase as a target against anticancer drugs, inhibition studies of a model enzyme, class II alpha-mannosidase from Aspergillus fischeri in presence of polyhydroxy piperidine derived glycosidase inhibitors, metal ions and amino acid specific reagents were carried out to reveal the sensitivity of the enzyme. Three of the derivatives (Compound 20, 32 and 39)(11) showed competitive inhibition (K(i) =45, 48 and 235 mu M) and the binding of the inhibitors to the enzyme was entropically driven. Among the metal ions checked, Cu(++) (K(i) = 21nm) and Se(++) ions (K(i) = 32 mu M) showed noncompetitive and Co(++) (K(i) = 1.195 mM) showed competitive inhibition of the enzyme activity with insignificant change in the secondary structure of the protein. The above studies exhibit the Potential of the enzyme in studying anticancer drugs. Treatment of the enzyme with group specific reagents showed the presence of carboxylate, Arg and Cys at the active site. Substrate protection studies and kinetics of the modified enzyme confirmed the above results. Trp and His at the active site were observed to be in proximity.

}, keywords = {active-site, alpha-Mannosidase, Chemical modification, Glycosidase inhibitors, metal ions}, issn = {0973-6263}, author = {Shashidhara, K. S. and Gaikwad, S. M. and Khan, Mohammad Islam and Bharadwaj, Kishor Chandra and Pandey, G.} } @article { ISI:000265921000002, title = {Purification and characterization of putative alkaline [Ni-Fe] hydrogenase from unicellular marine green alga, tetraselmis kochinensis NCIM 1605}, journal = {Microbiological Research}, volume = {164}, number = {2}, year = {2009}, month = {FEB}, pages = {131-137}, publisher = {ELSEVIER GMBH, URBAN \& FISCHER VERLAG}, address = {OFFICE JENA, P O BOX 100537, 07705 JENA, GERMANY}, abstract = {

Hydrogenase enzyme from the unicellular marine green alga Tetraselmis kochinensis NCIM 1605 was purified 467 fold to homogeneity. The molecular weight was estimated to be similar to 89kDa by SDS-PAGE. This enzyme consists of two subunits with molecular masses of similar to 70 and similar to 19 kDa. The hydrogenase was found to contain 10 g atoms of Fe and 1 g of atom of Ni per mote of protein. The specific activity of hydrogen evolution was 50 mu mol H-2/mg/h of enzyme using reduced methyl viologen as an electron donor. This hydrogenase enzyme has pl value similar to 9.6 representing its alkaline nature. The absorption spectrum of the hydrogenase enzyme showed an absorption peak at 425 nm indicating that the enzyme had iron-sulfur clusters. The total of 16 cysteine residues were found per mote of enzyme under the denaturing condition and 20 cysteine residues in reduced denatured enzyme indicating that it has two disulfide bridges. (C) 2007 Published by Elsevier GmbH.

}, keywords = {Characterization, Chemical modification, Ni-Fe hydrogenase, Tetraselmis kochinensis, Unicellular green algae}, issn = {0944-5013}, doi = {10.1016/j.micres.2006.11.006}, author = {Bhosale, Siddharth H. and Pant, A. and Khan, Mohammad Islam} } @article { ISI:000274401600036, title = {Steady state and time resolved fluorescence quenching and chemical modification studies of a lectin from endophytic fungus fusarium solani}, journal = {Journal of Fluorescence}, volume = {20}, number = {1}, year = {2010}, month = {JAN}, pages = {305-313}, publisher = {SPRINGER/PLENUM PUBLISHERS}, address = {233 SPRING ST, NEW YORK, NY 10013 USA}, abstract = {

The solute quenching studies of a lectin from endophytic fungus Fusarium solani were carried out using different quenchers such as acrylamide, succinimide, potassium iodide and cesium chloride. The lectin showed emission maximum at 348 nm indicating relative exposure of tryptophan. The quenchable fraction of the fluorophore was 100\% with acrylamide, whereas it was only 50\% with succinimide. The ionic quenchers iodide and cesium showed opposite effects at different pH. In the case of cesium, raising the pH resulted in increased quenching and accessibility of typtophan residue, while the iodide showed just opposite effect. These studies showed that the single tryptophan residue of the lectin (per monomer) is relatively exposed, and might be in the vicinity of positively charged amino acid residues. Various amino acids of the F. solani lectin were modified using different reagents to obtain information about the hemagglutinating site. The chemical modification studies suggested tyrosine residues can be modified using N-acetylimidazole, which results in complete loss of hemagglutination activity of the lectin. Kinetics of chemical modification suggested involvement of only 2 tyrosine residues. Modification of arginine, cysteine, histidine, lysine, aspartate, glutamate and tryptophan did not result in loss of hemagglutinating activity of the lectin.

}, keywords = {Chemical modification, fluorescence, Fusarium, Lectin, Quenching, Time-resolved}, issn = {1053-0509}, doi = {10.1007/s10895-009-0556-x}, author = {Khan, Feroz and Ahmad, Absar and Khan, Mohammad Islam} } @article { ISI:000324842900004, title = {Probing the active site of cinnamoyl CoA reductase 1 (Ll-CCRH1) from Leucaena leucocephala}, journal = {International Journal of Biological Macromolecules}, volume = {60}, year = {2013}, month = {SEP}, pages = {33-38}, publisher = {ELSEVIER SCIENCE BV}, address = {PO BOX 211, 1000 AE AMSTERDAM, NETHERLANDS}, abstract = {

Lack of three dimensional crystal structure of cinnamoyl CoA reductase (CCR) limits its detailed active site characterization studies. Putative active site residues involved in the substrate/NADPH binding and catalysis for Leucaena leucocephala CCR (Ll-CCRH1; GenBank: DQ986907) were identified by amino acid sequence alignment and homology modeling. Putative active site residues and proximal H215 were subjected for site directed mutagenesis, and mutated enzymes were expressed, purified and assayed to confirm their functional roles. Mutagenesis of S136, Y170 and K174 showed complete loss of activity, indicating their pivotal roles in catalysis. Mutant S212G exhibited the catalytic efficiencies less than 10\% of wild type, showing its indirect involvement in substrate binding or catalysis. R51G, D77G, F30V and I31N double mutants showed significant changes in K-m values, specifying their roles in substrate binding. Finally, chemical modification and substrate protection studies corroborated the presence Ser, Tyr, Lys, Arg and carboxylate group at the active site of Ll-CCRH1. (c) 2013 Elsevier B.V. All rights reserved.

}, keywords = {Chemical modification, Cinnamoyl CoA reductase 1, Docking simulations, homology modeling, Site directed mutagenesis, Substrate protection}, issn = {0141-8130}, doi = {10.1016/j.ijbiomac.2013.05.005}, author = {Sonawane, Prashant and Patel, Krunal and Vishwakarma, Rishi Kishore and Srivastava, Sameer and Singh, Somesh and Gaikwad, Sushama M. and Khan, Bashir Mohammad} } @article { ISI:000353218500003, title = {Crystal structure of a plant albumin from cicer arietinum (chickpea) possessing hemopexin fold and hemagglutination activity}, journal = {Planta}, volume = {241}, number = {5}, year = {2015}, month = {MAY}, pages = {1061-1073}, publisher = {SPRINGER}, address = {233 SPRING ST, NEW YORK, NY 10013 USA}, abstract = {

Crystal structure of a reported PA2 albumin from Cicer arietinum shows that it belongs to hemopexin fold family, has four beta-propeller motifs and possesses hemagglutination activity, making it different from known legume lectins. A plant albumin (PA2) from Cicer arietinum, presumably a lectin (CAL) owing to its hemagglutination activity which is inhibited by complex sugars as well as glycoproteins such as fetuin, desialylated fetuin and fibrinogen. The three-dimensional structure of this homodimeric protein has been determined using X-ray crystallography at 2.2 in two crystal forms: orthorhombic (P2(1)2(1)2) and trigonal (P3). The structure determined using molecular replacement method and refined in orthorhombic crystal form reached R-factors R (free) 22.6 \% and R (work) 18.2 \% and in trigonal form had 22.3 and 17.9 \% in the resolution range of 20.0-2.2 and 35.3-2.2 , respectively. Interestingly, unlike the known legume lectin fold, the structure of this homodimeric hemagglutinin belonged to hemopexin fold that consisted of four-bladed beta-propeller architecture. Each subunit has a central cavity forming a channel, inside of which is lined with hydrophobic residues. The channel also bears binding sites for ligands such as calcium, sodium and chloride ions, iodine atom in the case of iodine derivative and water molecules. However, none of these ligands seem important for the sugar recognition. No monosaccharide sugar specificity could be detected using hemagglutination inhibition. Chemical modification studies identified a potential sugar-binding site per subunit molecule. Comparison of C-alpha atom positions in subunit structures showed that the deviations between the two crystal forms were more with respect to blades I and IV. Differences also existed between subunits in two forms in terms of type and site of ligand binding.

}, keywords = {Beta-propeller fold, Chemical modification, Chickpea lectin, Complex sugars, PA2 albumin, Sugar binding}, issn = {0032-0935}, doi = {10.1007/s00425-014-2236-6}, author = {Sharma, Urvashi and Katre, Uma V. and Suresh, C. G.} } @article {46072, title = {Aromatic polyesters containing pendant azido groups: synthesis, characterization, chemical modification and thermal cross-linking}, journal = {European Polymer Journal}, volume = {116}, year = {2019}, month = {JUL}, pages = {180-189}, type = {Article}, abstract = {

A partially bio-based bisphenol containing pendant azido group viz., 4,4{\textquoteright}-(5-azidopentane-2,2-diyl) diphenol (AZBPA) was synthesized starting from 4,4{\textquoteright}-bis (4-hydroxyphenyl) pentanoic acid. AZBPA was reacted with isophthaloyl chloride (IPC), terephthaloyl chloride (TPC) and a mixture of IPC/TPC (50:50 mol\%) by phase transfer-catalyzed interfacial polycondensation route to obtain aromatic polyesters containing pendant azido groups. Copolyesters containing pendant azido groups were also synthesized by polycondensation of different molar proportions of AZBPA and commercially available 4,4{\textquoteright}-(1-phenylethane-1,1-diyl) diphenol (BPA-AP) with IPC. Inherent viscosities and number average molecular weights of (co)polyesters were in the range 0.85-1.64 dL/g and 58,900-190,400, respectively, indicating the formation of reasonably high molecular weight polymers. Tough, transparent, and flexible films could be cast from chloroform solutions of these polyesters. X-Ray diffraction analysis showed that (co)polyesters were amorphous in nature. (Co)polyesters were characterized using FT-IR, H-1 NMR spectroscopy, XRD, TGA and DSC analysis. The chemical modification of a representative copolyester containing pendant azido groups was carried out quantitatively using copper-catalyzed azide-alkyne cycloaddition (CuAAC) with two alkynes viz., phenyl acetylene (PA) and ethynyl-4-nitrobenzene (ENB). Additionally, (co)polyesters containing pendant azido groups were thermally cross-linked (170 degrees C/12 h) leading to the formation of network structures based on azide to nitrene decomposition and subsequent reactions on polyester backbone. The selected cross-linked polyesters were characterized by stress-strain measurements. The cross-linked polymers exhibited higher tensile strength and Young{\textquoteright}s modulus and lower \% elongation at break compared to corresponding pristine polyesters containing pendant azido groups.

}, keywords = {Aromatic polyester, Chemical modification, Click chemistry, Pendant azido group, Thermal cross-linking}, issn = {0014-3057}, doi = {10.1016/j.eurpolymj.2019.04.019}, author = {Nagane, Samadhan S. and Verma, Savita and Tawade, V, Bhausaheb and Sane, Prakash S. and Dhanmane, Sushilkumar A. and Wadgaonkar, Prakash P.} } @article {46059, title = {New cardo bisphenol monomer containing pendant azido group and the resulting aromatic polyesters}, journal = {Journal of Polymer Science Part A-Polymer Chemistry}, volume = {57}, year = {2019}, month = {JUL }, pages = {1516-1526}, type = {Article}, abstract = {

Expanding on our strategy to synthesize aromatic step-growth polymers containing pendant clickable azido groups via functional monomer approach, we have now designed and synthesized a new cardo bisphenol, viz., 2-(2-azidoethyl)-3, 3-bis(4-hydroxyphenyl) isoindolin-1-one (PPH-N-3). PPH-N-3 was conveniently synthesized starting from commercially available phenolphthalein by a three-step route in an overall yield of 65\% using simple organic transformations. Aromatic (co)polyesters bearing pendant azido groups were synthesized by low-temperature solution polycondensation of PPH-N-3 or different molar ratios of PPH-N-3 and bisphenol-A (BPA) with aromatic diacid chlorides in dry dichloromethane in the presence of triethylamine (TEA) as a base. The formation of medium to reasonably high-molecular-weight (co)polyesters was evidenced from intrinsic viscosity and number-average molecular-weight measurements that were in the range 0.52-0.85 dL/g and 16,700-28,200, respectively. Tough, transparent, and flexible films could be cast from chloroform solutions of these (co)polyesters. (Co)polyesters were characterized using FTIR, H-1 NMR, C-13 NMR spectroscopy, XRD, and TGA. The thermal curing reaction of (co)polyesters involving decomposition of azido groups was studied by DSC analysis. The chemical modification of a representative copolyester containing pendant azido groups was carried out quantitatively using catalyst-free azide-maleimide cycloaddition reaction with two maleimides, namely, N-methylmaleimide and N-hexylmaleimide. (c) 2019 Wiley Periodicals, Inc.

}, keywords = {aromatic (co)polyester, azido group, cardo bisphenol, Chemical modification}, issn = {0887-624X}, doi = {10.1002/pola.29414}, author = {Maher, Deepak M. and Nagane, Samadhan S. and Jadhav, Uday A. and Salunkhe, Pravin H. and Tawade, Bhausaheb V. and Wadgaonkar, Prakash P.} } @article {48145, title = {Pendant propargyloxy-functionalized aromatic (co)polycarbonates: synthesis, thermal crosslinking and chemical modification}, journal = {Journal of Macromolecular Science Part A-Pure and Applied Chemistry}, volume = {59}, year = {2022}, month = {NOV}, pages = {752-763}, type = {Article}, abstract = {

A bisphenol monomer bearing pendant propargyloxy group viz, 1, 1-bis (4-hydoxyphenyl)-1-(4 {\textquoteleft}-propargyloxyphenyl) ethane (BPP) was synthesized starting from commercially available 1, 1, 1-tris (4-hydroxyphenyl) ethane (THPE) by mono O-propargylation reaction using propargyl bromide. A new series of pendant propargyloxy-functionalized aromatic (co)polycarbonates was synthesized by low-temperature solution polycondensation of BPP or different molar ratios of BPP and bisphenol-A with triphosgene in dichloromethane in the presence of triethylamine. The formation of reasonably high molecular weight (co)polycarbonates was confirmed by inherent viscosity (0.52-0.83 dL/g) and gel permeation chromatography (M-n 37,000-69,800 g/mol, polystyrene standards) measurements. C-13 NMR spectral studies supported formation of random copolycarbonates in copolymerization of BPP and BPA with triphosgene. The 10\% weight loss temperature (T-10) values of (co)polycarbonates, determined by thermogravimetric analysis under nitrogen atmosphere, were in the range 427-438 degrees C indicating their good thermal stability. The glass transition temperature (T-g) values of (co)polycarbonates were observed in the range 147-152 degrees C. The crosslinking ability of (co)polycarbonates involving pendant propargyloxy groups leading to formation of networked structure was evaluated via non-isothermal curing studies by DSC. As a proof-of-concept, the post-modification of a representative polycarbonate bearing pendant propargyloxy groups with 1-octane thiol as a model compound via thiol-yne click reaction was briefly studied.

}, keywords = {Aromatic polycarbonate, Chemical modification, propargyloxy groups, thermal crosslinking, thiol-yne click reaction}, issn = {1060-1325}, doi = {10.1080/10601325.2022.2117055}, author = {Nagane, Samadhan S. and Maher, Deepak M. and Verma, Savita and Talanikar, Aniket A. and Wadgaonkar, Prakash P.} }