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Open AccessArticle

Protein GB1 Folding and Assembly from Structural Elements

by Mikael C. Bauer 1,*, Wei-Feng Xue 1, 2 and Sara Linse 1,*
Department of Biophysical Chemistry, Lund University, Chemical Center, SE-22100 Lund, Sweden
Present address: Astbury Centre for Structural Molecular Biology, University of Leeds, LS2 9JT, Leeds, UK
Authors to whom correspondence should be addressed.
Int. J. Mol. Sci. 2009, 10(4), 1552-1566;
Received: 11 February 2009 / Revised: 20 March 2009 / Accepted: 31 March 2009 / Published: 8 April 2009
(This article belongs to the Special Issue Protein Folding 2009)
Folding of the Protein G B1 domain (PGB1) shifts with increasing salt concentration from a cooperative assembly of inherently unstructured subdomains to an assembly of partly pre-folded structures. The salt-dependence of pre-folding contributes to the stability minimum observed at physiological salt conditions. Our conclusions are based on a study in which the reconstitution of PGB1 from two fragments was studied as a function of salt concentrations and temperature using circular dichroism spectroscopy. Salt was found to induce an increase in β-hairpin structure for the C-terminal fragment (residues 41 – 56), whereas no major salt effect on structure was observed for the isolated N-terminal fragment (residues 1 – 41). In line with the increasing evidence on the interrelation between fragment complementation and stability of the corresponding intact protein, we also find that salt effects on reconstitution can be predicted from salt dependence of the stability of the intact protein. Our data show that our variant (which has the mutations T2Q, N8D, N37D and reconstitutes in a manner similar to the wild type) displays the lowest equilibrium association constant around physiological salt concentration, with higher affinity observed both at lower and higher salt concentration. This corroborates the salt effects on the stability towards denaturation of the intact protein, for which the stability at physiological salt is lower compared to both lower and higher salt concentrations. Hence we conclude that reconstitution reports on molecular factors that govern the native states of proteins. View Full-Text
Keywords: Protein folding; protein reconstitution; fragment complementation; prefolding; electrostatic interactions; salt screening Protein folding; protein reconstitution; fragment complementation; prefolding; electrostatic interactions; salt screening
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Bauer, M.C.; Xue, W.-F.; Linse, S. Protein GB1 Folding and Assembly from Structural Elements. Int. J. Mol. Sci. 2009, 10, 1552-1566.

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