Exploration of partially unfolded states of human alpha-lactalbumin by molecular dynamics simulation.
Molecular dynamics simulations are used to probe the properties of non-native states of the protein human alpha-lactalbumin (human alpha-LA) with a detailed atomistic model in an implicit aqueous solvent environment. To sample the conformational space, a biasing force is introduced that increases the radius of gyration relative to the native state and generates a large number of low-energy conformers that differ in terms of their root-mean-square deviation, for a given radius of gyration. The resulting structures are relaxed by unbiased simulations and used as models of the molten globule and partly denatured states of human alpha-LA, based on measured radii of gyration obtained from nuclear magnetic resonance experiments. The ensembles of structures agree in their overall properties with experimental data available for the human alpha-LA molten globule and its more denatured states. In particular, the simulation results show that the native-like fold of the alpha-domain is preserved in the molten globule. Further, a considerable proportion of the antiparallel beta-strand in the beta-domain are present. This indicates that the lack of hydrogen exchange protection found experimentally for the beta-domain is due to rearrangement of the beta-sheet involving transient populations of non-native beta-structures. The simulations also provide details concerning the ensemble of structures that contribute as the molten globule unfolds and shows, in accord with experimental data, that unfolding is not cooperative; i.e. the various structural elements do not unfold simultaneously.
Paci
E
E
Oxford Centre for Molecular Sciences, New Chemistry Laboratory, University of Oxford, South Parks Road, Oxford, OX1 3QT, UK.
Smith
L J
LJ
Dobson
C M
CM
Karplus
M
M
D001665:Binding Sites; D003198:Computer Simulation; D018360:Crystallography, X-Ray; D006801:Humans; D007768:Lactalbumin / Q000737:chemistry* / Q000378:metabolism*; D008958:Models, Molecular; D011489:Protein Denaturation / Q000187:drug effects; D017510:Protein Folding; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D013816:Thermodynamics; D014508:Urea / Q000494:pharmacology
D014508:Urea; D007768:Lactalbumin