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J Mol Biol. 2006 Jan 6;355(1):2-8. Epub 2005 Nov 8.

Observing folding pathways and kinetics of a single sodium-proton antiporter from Escherichia coli.

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Center of Biotechnology, University of Technology, 01307 Dresden, Germany.


Mechanisms of folding and misfolding of membrane proteins are of interest in cell biology. Recently, we have established single-molecule force spectroscopy to observe directly the stepwise folding of the Na+/H+ antiporter NhaA from Escherichia coli in vitro. Here, we improved this approach significantly to track the folding intermediates of a single NhaA polypeptide forming structural segments such as the Na+-binding site, transmembrane alpha-helices, and helical pairs. The folding rates of structural segments ranged from 0.31 s(-1) to 47 s(-1), providing detailed insight into a distinct folding hierarchy of an unfolded polypeptide into the native membrane protein structure. In some cases, however, the folding chain formed stable and kinetically trapped non-native structures, which could be assigned to misfolding events of the antiporter.

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