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pH and heat‐dependent behaviour of glucose oxidase down to single molecule level by combined fluorescence spectroscopy and molecular modelling
Author(s) -
Dumitraşcu Loredana,
Stănciuc Nicoleta,
Bahrim Gabriela Elena,
Ciumac Alexandrina,
Aprodu Iuliana
Publication year - 2016
Publication title -
journal of the science of food and agriculture
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.782
H-Index - 142
eISSN - 1097-0010
pISSN - 0022-5142
DOI - 10.1002/jsfa.7296
Subject(s) - glucose oxidase , chemistry , conformational change , chromophore , molecule , fluorescence spectroscopy , quenching (fluorescence) , flavin group , molecular dynamics , spectroscopy , photochemistry , fluorescence , analytical chemistry (journal) , biophysics , enzyme , biochemistry , chromatography , organic chemistry , computational chemistry , physics , quantum mechanics , biology
BACKGROUND In the food industry, glucose oxidase ( GOX ) is used to improve the shelf life of food materials. The pH ‐ and heat‐induced conformational changes of glucose oxidase from Aspergillus niger were quantified by means of fluorescence spectroscopy and molecular dynamics simulations. RESULTS The phase diagram showed an all‐or‐none transition process, indicating that pH and temperature largely influence the conformational state of GOX . Shifts in maximum wavelength of Trp, Tyr were registered as the protein encounters a lower pH ( pH 4.0), suggesting significant changes of the polarity around the chromophore molecule. Quenching experiments using KI showed higher quenching constants of Trp and flavin adenine dinucleotide upon heating or by changing pH value, and were mainly correlated with the conformational changes upon protein matrix. Finally, valuable insights into the thermal behaviour of GOX were obtained from molecular modelling results. CONCLUSIONS The conformation and structure of GOX protein is dependent upon the pH and heat treatment applied. Molecular dynamics simulation indicated significant changes in the substrate binding region at temperatures over 60°C that might affect enzyme activity. Moreover, an important alteration of the small pocket hosting the positively charged His 516 residue responsible for oxygen activation appears evident at high temperatures. © 2015 Society of Chemical Industry