title: Characterization of an alternative low energy fold for bovine α-lactalbumin formed by disulfide bond shuffling.
abstract: Bovine α-lactalbumin (αLA) forms a misfolded disulfide bond shuffled isomer, X-αLA. This X-αLA isomer contains two native disulfide bridges (Cys 6-Cys 120 and Cys 28-Cys 111) and two non-native disulfide bridges (Cys 61-Cys 73 and Cys 77-Cys 91). MD simulations have been used to characterize the X-αLA isomer and its formation via disulfide bond shuffling and to compare it with the native fold of αLA. In the simulations of the X-αLA isomer the structure of the α-domain of native αLA is largely retained in agreement with experimental data. However, there are significant rearrangements in the β-domain, including the loss of the native β-sheet and calcium binding site. Interestingly, the energies of X-αLA and native αLA in simulations in the absence of calcium are closely similar. Thus, the X-αLA isomer represents a different low energy fold for the protein. Calcium binding to native αLA is shown to help preserve the structure of the β-domain of the protein limiting possibilities for disulfide bond shuffling. Hence, binding calcium plays an important role in both maintaining the native structure of αLA and providing a mechanism for distinguishing between folded and misfolded species.
authors.affiliation: Department of Chemistry, University of Oxford, Inorganic Chemistry Laboratory, South Parks Road, Oxford OX1 3QR, United Kingdom.
authors.forename: Sarah
authors.initials: S
authors.lastname: Lewney
authors.forename: Lorna J
authors.initials: LJ
authors.lastname: Smith
mesh_terms: D000818:Animals; D001665:Binding Sites; D002118:Calcium / Q000378:metabolism; D002417:Cattle; D004220:Disulfides / Q000737:chemistry* / Q000378:metabolism; D007768:Lactalbumin / Q000737:chemistry* / Q000378:metabolism; D056004:Molecular Dynamics Simulation; D017510:Protein Folding; D017434:Protein Structure, Tertiary; D013816:Thermodynamics
chemical_list: D004220:Disulfides; D007768:Lactalbumin; D002118:Calcium