@article { ISI:000250755100004, title = {Fluorescence quenching and time-resolved fluorescence studies of alpha-Mannosidase from Aspergillus fischeri (NCIM 508)}, journal = {Journal of Fluorescence}, volume = {17}, number = {6}, year = {2007}, month = {NOV}, pages = {599-605}, publisher = {SPRINGER/PLENUM PUBLISHERS}, type = {Article}, address = {233 SPRING ST, NEW YORK, NY 10013 USA}, abstract = {

Apart from the vital role in glycoprotein biosynthesis and degradation, alpha-mannosidase is currently an important therapeutic target for the development of anticancer agents. Fluorescence quenching and time-resolved fluorescence of alpha-mannosidase, a multitryptophan protein from Aspergillus fischeri were carried out to investigate the tryptophan environment. The tryptophans were found to be differentially exposed to the solvent and were not fully accessible to the neutral quencher indicating heterogeneity in the environment. Quenching of the fluorescence by acrylamide was collisional. Surface tryptophans were found to have predominantly positively charged amino acids around them and differentially accessible to the ionic quenchers. Denaturation led to more exposure of tryptophans to the solvent and consequently in the significant increase in quenching with all the quenchers. The native enzyme showed two different lifetimes, tau (1) (1.51 ns) and tau (2) (5.99 ns). The average lifetime of the native protein (tau) (3.187 ns) was not affected much after denaturation (tau) (3.219 ns), while average lifetime of the quenched protein samples was drastically reduced (1.995 ns for acrylamide and 1.537 ns for iodide). This is an attempt towards the conformational studies of alpha-mannosidase.

}, keywords = {alpha-Mannosidase, Denaturation, fluorescence, lifetime, Solute quenching}, issn = {1053-0509}, doi = {10.1007/s10895-007-0227-8}, author = {Shashidhara, K. S. and Gaikwad, Sushama M.} } @article { ISI:000253896400027, title = {Steady state and time-resolved fluorescence studies of a hemagglutinin from Moringa oleifera}, journal = {Journal of Fluorescence}, volume = {18}, number = {2}, year = {2008}, month = {MAR}, pages = {479-485}, publisher = {SPRINGER/PLENUM PUBLISHERS}, address = {233 SPRING ST, NEW YORK, NY 10013 USA}, abstract = {

The saccharide binding and conformational characterization of a hemagglutinin, a low molecular weight protein from the seeds of Moringa oleifera was studied using steady state and time resolved fluorescence. The lectin binds sugars LacNAc (K-a = 1380 M-1) and fructose (K-a = 975 M-1), as determined by the fluorescence spectroscopy. It has a single tryptophan per monomer which is exposed on the surface and is in a strong electropositive environment as revealed by quenching with iodide. Quenching of the fluorescence by acrylamide involved both static (K-s = 0.216 M-1) and collisional (K-sv= 8.19 M-1) components. The native protein showed two different lifetimes, tau(1) (1.6 ns) and tau(2) (4.36 ns) which decrease and get converted into a single one, (2.21 ns) after quenching with 0.15 M acrylamide. The bimolecular quenching constant, k(q) was 7.55 x 10(11) M-1 s(-1). ANS binding studies showed that the native protein has exposed hydrophobic patches which get further exposed at extreme acidic or alkaline pH. However, they get buried in the interior of the protein in presence of 1 M GdnHCl or urea.

}, keywords = {ANS binding, fluorescence, Hemagglutinin, lifetime, Moringa oleifera, saccharide binding, Solute quenching}, issn = {1053-0509}, doi = {10.1007/s10895-007-0289-7}, author = {Katre, Uma V. and Suresh, C. G. and Khan, Mohammad Islam and Gaikwad, Sushama M.} } @article { ISI:000336733100003, title = {Steady state fluorescence studies of wild type recombinant cinnamoyl CoA reductase (Ll-CCRH1) and its active site mutants}, journal = {Journal of Fluorescence}, volume = {24}, number = {3}, year = {2014}, month = {MAY}, pages = {665-673}, publisher = {SPRINGER/PLENUM PUBLISHERS}, address = {233 SPRING ST, NEW YORK, NY 10013 USA}, abstract = {

Fluorescence quenching and time resolved fluorescence studies of wild type recombinant cinnamoyl CoA reductase (Ll-CCRH1), a multitryptophan protein from Leucaena leucocephala and 10 different active site mutants were carried out to investigate tryptophan environment. The enzyme showed highest affinity for feruloyl CoA (K (a) = 3.72 x 10(5) M-1) over other CoA esters and cinnamaldehydes, as determined by fluorescence spectroscopy. Quenching of the fluorescence by acrylamide for wild type and active site mutants was collisional with almost 100 \% of the tryptophan fluorescence accessible under native condition and remained same after denaturation of protein with 6 M GdnHCl. In wild type Ll-CCRH1, the extent of quenching achieved with iodide (f (a) = 1.0) was significantly higher than cesium ions (f (a) = 0.33) suggesting more density of positive charge around surface of trp conformers under native conditions. Denaturation of wild type protein with 6 M GdnHCl led to significant increase in the quenching with cesium (f (a) = 0.54), whereas quenching with iodide ion was decreased (f (a) = 0.78), indicating reorientation of charge density around trp from positive to negative and heterogeneity in trp environment. The Stern-Volmer plots for wild type and mutants Ll-CCRH1 under native and denatured conditions, with cesium ion yielded biphasic quenching profiles. The extent of quenching for cesium and iodide ions under native and denatured conditions observed in active site mutants was significantly different from wild type Ll-CCRH1 under the same conditions. Thus, single substitution type mutations of active site residues showed heterogeneity in tryptophan microenvironment and differential degree of conformation of protein under native or denatured conditions.

}, keywords = {Active site mutants, Cinnamoyl CoA reductase, fluorescence, Ligand binding, Solute quenching}, issn = {1053-0509}, doi = {10.1007/s10895-013-1343-2}, author = {Sonawane, Prashant and Vishwakarma, Rishi Kishore and Singh, Somesh and Gaikwad, Sushama M. and Khan, Bashir Mohammad} }