Effects of soman inhibition and of structural differences on cholinesterase molecular dynamics: A neutron scattering study
Frank Gabel 1, Martin Weik 1*, Patrick Masson 2, Frederique Renault 2, Didier Fournier 3, Laure Brochier 3, Bhupendra P Doctor 4, Ashima Saxena 4, Israel Silman 5 and Giuseppe Zaccai 1
1 Institut de Biologie Structurale
2 CRSSA, La Tronche, France
3 IPBS, Toulouse, France
4 Walter Reed Army Institute of Research, Washington
5 Weizmann Institute of Science, Rehovot, Israel
* To whom correspondence should be addressed. E-mail: weik{at}ibs.fr.
Submitted on February 9, 2005
Revised on April 4, 2005
Accepted on 30 June 2005
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Abstract |
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Incoherent elastic neutron scattering experiments on members of the cholinesterase family were carried out in order to investigate how molecular dynamics is affected by covalent inhibitor binding and by differences in primary and quarternary structure. Tetrameric native and soman-inhibited human butyrylcholinesterase (HuBChE) as well as native dimeric Drosophila melanogaster acetylcholinesterase (DmAChE) hydrated protein powders were examined. Atomic mean square displacements (MSDs) were found to be identical for native HuBChE and for DmAChE in the whole temperature range examined, leading to the conclusion that differences in activity and substrate specificity are not reflected by a global modification of sub-nanosecond molecular dynamics. MSDs of native and soman-inhibited HuBChE were identical below the thermal denaturation temperature of the native enzyme, indicating a common mean free energy surface. Denaturation of the native enzyme is reflected by a relative increase of MSDs consistent with entropic stabilization of the unfolded state. The results suggest that the stabilization of HuBChE phosphonylated by soman is due to an increase in free energy of the unfolded state due to a decrease in entropy.
Key Words:
incoherent elastic neutron scattering, ligand binding, protein flexibility, protein stability, thermal fluctuations
