@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:000262769700020, title = {Class II alpha-mannosidase from aspergillus fischeri: energetics of catalysis and inhibition}, journal = {International Journal of Biological Macromolecules}, volume = {44}, number = {1}, year = {2009}, month = {JAN}, pages = {112-115}, publisher = {ELSEVIER SCIENCE BV}, address = {PO BOX 211, 1000 AE AMSTERDAM, NETHERLANDS}, abstract = {

Energetics of the catalysis of Class II alpha-mannosidase (E.C.3.2.1.24) from Aspergillus fischeri was studied. The enzyme showed K(cat)/K(m) for Man (alpha 1-3) Man, Man (alpha 1-2) Man and Man (alpha 1-6) Man as 7488, 5376 and 3690 M(-1) min(-1), respectively. The activation energy, Ea was 15.14, 47.43 and 71.21 kJ/mol for a1-3, alpha 1-2 and alpha 1-6 linked mannobioses, respectively, reflecting the energy barrier in the hydrolysis of latter two substrates. The enzyme showed K(cat)/K(m) as 3.56 x 10(5) and 4.61 x 10(5) M(-1) min(-1) and E(a) as 38.7 and 8.92 kJ/mol, towards pNP alpha Man and 4-MeUmb alpha Man, respectively. Binding of Swainsonine to the enzyme is stronger than that of 1-deoxymannojirimycin. (C) 2008 Elsevier B.V. All rights reserved.

}, keywords = {alpha-Mannosidase, Energy of activation, kinetics, Swainsonine}, issn = {0141-8130}, doi = {10.1016/j.ijbiomac.2008.10.012}, author = {Shashidhara, K. S. and Gaikwad, Sushama M.} } @article { ISI:000280597500004, title = {Conformational and functional transitions in class II alpha-mannosidase from aspergillus fischeri}, journal = {Journal of Fluorescence}, volume = {20}, number = {4}, year = {2010}, month = {JUL}, pages = {827-836}, publisher = {SPRINGER/PLENUM PUBLISHERS}, address = {233 SPRING ST, NEW YORK, NY 10013 USA}, abstract = {

The conformational transitions in an oligomeric and high molecular weight class II alpha-mannosidase from Aspergillus fischeri were examined using fluorescence and CD spectroscopy under chemical, thermal and acid denaturing conditions. The enzyme lost the activity first and then the overall folded conformation and secondary structure. The midpoint values of GdnHCl mediated changes measured by inactivation; fluorescence and negative ellipticity were 0.48 M, 1.5 M and 1.9 M, respectively. The protein almost completely unfolded in 4.0 M GdnHCl but not at 90 A degrees C. The inactivation and unfolding were irreversible. At pH 2.0, the protein exhibited molten-globule like intermediate with rearranged secondary and tertiary structures and exposed hydrophobic amino acids on the surface. This species showed increased accessibility of Trp to the quenchers and got denatured with GdnHCl in a different manner. The insoluble aggregates of a thermally denatured protein could be detected only in the presence of 0.25-0.75 M GdnHCl.

}, keywords = {Aggregation, alpha-Mannosidase, ANS binding, Circular dichroism, fluorescence, GdnHCl, Hydrobicity, Thermal denaturation}, issn = {1053-0509}, doi = {10.1007/s10895-010-0625-1}, author = {Shashidhara, K. S. and Gaikwad, Sushama M.} } @article { ISI:000286021300025, title = {Multistate unfolding of alpha-mannosidase from Canavalia ensiformis (Jack Bean): evidence for the thermostable molten globule}, journal = {Biochemical and Biophysical Research Communications}, volume = {403}, number = {3-4}, year = {2010}, month = {DEC}, pages = {391-397}, publisher = {ACADEMIC PRESS INC ELSEVIER SCIENCE}, address = {525 B ST, STE 1900, SAN DIEGO, CA 92101-4495 USA}, abstract = {

The relevance of partially ordered states of proteins (such as the molten-globule state) in cellular processes is beginning to be understood. We examined the conformational transitions in a multimeric and high molecular weight class II alpha-mannosidase from Canavalia ensiformis (Jack Bean) (Jb alpha-man) utilizing intrinsic fluorescence, solute quenching, hydrophobic dye binding, size exclusion chromatography and circular dichroism (CD) spectroscopy for the protein in presence of Guanidine hydrochloride (GdnHCl). The decomposition analysis of the protein spectra obtained during unfolding showed progressive appearance of class S, I, II and III trp. The parameter A and spectral center of mass showed multi state unfolding of the protein and phase diagram analysis revealed formation of an intermediate of Jb alpha-man in the vicinity of 1 M GdnHCl. The intermediate exhibited compact secondary and distorted tertiary structure with exposed hydrophobic amino acids on the surface, indicating the molten-globule nature. The dissociation, partial unfolding and aggregation of Jb alpha-man occurred simultaneously during chemical denaturation. The molten-globule possessed slightly higher hydrodynamic radius, perturbance in the structure up to 60 degrees C and stability of the structure up to 80 degrees C unlike the native Jack Bean alpha-mannosidase. The modes of chemical and thermal denaturation of the native protein were different. The solute quenching parameters confirmed the altered confirmation of the intermediate. Taken together, our results constitute one of the early reports of formation of GdnHCl induced molten globule in a class II alpha-mannosidase. (C) 2010 Elsevier Inc. All rights reserved.

}, keywords = {alpha-Mannosidase, Circular dichroism, fluorescence, Guanidine hydrochloride, Molten globule, Thermostability, Unfolding}, issn = {0006-291X}, doi = {10.1016/j.bbrc.2010.11.041}, author = {Kumar, Avinash and Gaikwad, Sushama M.} } @article { ISI:000296937200031, title = {Jack bean alpha-mannosidase (Jb alpha-man): tolerance to alkali, chelating and reducing agents and energetics of catalysis and inhibition}, journal = {International Journal of Biological Macromolecules}, volume = {49}, number = {5}, year = {2011}, month = {DEC}, pages = {1066-1071}, publisher = {ELSEVIER SCIENCE BV}, address = {PO BOX 211, 1000 AE AMSTERDAM, NETHERLANDS}, abstract = {

Investigations of the catalytic and structural transitions of jack bean alpha-mannosidase (Jb alpha-man) are described in the present paper. The enzyme was maximally stable at pH 5.0; however, when incubated in the pH range of 11.0-12.0, showed 1.3 times higher activity and also stability for longer time. The free amino group at or near the active site was probably involved in the stability and activation mechanism. The active site is constituted by the association of two unidentical subunits connected by disulfide linkages. The metalloenzyme has Zn(2+) ions tightly bound and chelation reduces the thermal stability of the protein. Energetics of catalysis and thermodynamics of inhibition of the enzyme were also carried out. (C) 2011 Elsevier B.V. All rights reserved.

}, keywords = {Alkali tolerance, alpha-Mannosidase, beta-Mercaptoethanol, Energetics, Inhibition, Metalloenzyme}, issn = {0141-8130}, doi = {10.1016/j.ijbiomac.2011.08.033}, author = {Kumar, Avinash and Gaikwad, Sushama M.} }