科研之友
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摘要
Metal ions are ubiquitous in protein systems and play a significant role during their folding processes. Nineteen independent structures were determined for the Na+/beta-hairpin interacting systems, and their folding pathways are different. (i) For Na-S47, the turn is rapidly shaped with the help of Na+ and acts as the folding nucleus for the rest regions. Two intermediate states are observed and the resulted structure is the most folded. (ii) For Na-B41, Na-B52, Na-B54, Na-S55 and Na-B56, the inclusive Na+ ions are anchored by beta-strands. The local structures around the Na+ ions and the i:urn regions fold simultaneously and serve as two independent folding nuclei. (iii) The other systems have no folding nuclei and correspond to low-folded structures. Long-range electrostatic interactions contribute a lot to the folding, especially from the four negatively charged residues (Glu42, Asp46, Asp47 and Glu56). The initial positions of the Na+ ions are largely responsible for the different folding behaviors. The interactions with sidechain- rather than backbone-O atoms generally lead to more compact structures. Another factor affecting the folding is whether the 0 atoms are associated with native I-I-bonds, and those involved show decreased affinities to metal ions. The addition of water solvent does not induce obvious folding and conformational transitions to the Na+/beta-hairpin interacting systems.
