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Structural stability of human butyrylcholinesterase under high hydrostatic pressure
Affiliation:1. Institute of Physics, University of Tartu, W. Ostwald Str. 1, Tartu 51011, Estonia;2. Université Grenoble Alpes, CNRS, LiPhy, Grenoble 38000, France;3. Institut Laue Langevin, 71 avenue des Martyrs, Grenoble Cedex 38042, France;4. Neuropharmacology Laboratory, Kazan Federal University, Kazan, Russia;5. Institute of Molecular and Cell Biology, University of Tartu, Riia 23, Tartu 51014, Estonia;1. Graduate School of Environmental and Life Sciences, Okayama University, 1-1-1, Tsushima-naka, Okayama 700-8530, Japan;2. Faculty of Life Sciences and Institute for Protein Dynamics, Kyoto Sangyo University, Kyoto 603-8555, Japan;3. Institute for Quantitative Biosciences, The University of Tokyo, Tokyo 113-0032, Japan
Abstract:Human butyrylcholinesterase is a nonspecific enzyme of clinical, pharmacological and toxicological significance. Although the enzyme is relatively stable, its activity is affected by numerous factors, including pressure. In this work, hydrostatic pressure dependence of the intrinsic tryptophan fluorescence in native and salted human butyrylcholinesterase was studied up to the maximum pressure at ambient temperature of about 1200 MPa. A correlated large shift toward long wavelengths and broadening observed at pressures between 200 and 700 MPa was interpreted as due to high pressure-induced denaturation of the protein, leading to an enhanced exposure of tryptophan residues into polar solvent environment. This transient process in native butyrylcholinesterase presumably involves conformational changes of the enzyme at both tertiary and secondary structure levels. Pressure-induced mixing of emitting local indole electronic transitions with quenching charge transfer states likely describes the accompanying fluorescence quenching that reveals different course from spectral changes. All the pressure-induced changes turned irreversible after passing a mid-point pressure of about 400 ± 50 MPa. Addition of either 0.1 M ammonium sulphate (a kosmotropic salt) or 0.1 M lithium thiocyanate (a chaotropic salt) to native enzyme similarly destabilized its structure.
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