Biochemical and Biophysical Research Communications, Vol.508, No.1, 270-274, 2019
beta-sheet to alpha-helix conversion and thermal stability of beta-Galactosidase encapsulated in a nanoporous silica gel
The effect on protein conformation and thermal stability was studied for beta-Galactosidase (beta-Gal) encapsulated in the nanopores of a silicate matrix (E beta-Gal). Circular dichroism spectra showed that, compared with the enzyme in buffer (S beta-Gal), E beta-Gal exhibited a higher content of alpha-helix structure. Heating E beta-Gal up to 75 degrees C caused a decrease in the content of 13-sheet structure and additional augments on E beta-Gal components attributed to helical content, instead of the generalized loss of the ellipticity signal observed with S beta-Gal. Steady state fluorescence spectroscopy analysis evidenced an E beta-Gal structure less compact and more accessible to solvent and also less stable against temperature increase. While for S beta-Gal the denaturation midpoint (Tm) was 59 degrees C, for E(beta-Gal)it was 48 degrees C. The enzymatic activity assays at increasing temperatures showed that in both conditions, the enzyme lost most of its hydrolytic activity against ONPG at temperatures above 65 degrees C and E beta-Gal did it even at lower T values. Concluding, confinement in silica nanopores induced conformational changes on the tertiary/cuaternary structure of E beta-Gal leading to the loss of thermal stability and enzymatic activity. (C) 2018 Elsevier Inc. All rights reserved.