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Science 334 (6055): 512-516

Copyright © 2011 by the American Association for the Advancement of Science

The Complex Folding Network of Single Calmodulin Molecules

Johannes Stigler,1 Fabian Ziegler,1 Anja Gieseke,1 J. Christof M. Gebhardt,1,* Matthias Rief1,2,{dagger}

Abstract: Direct observation of the detailed conformational fluctuations of a single protein molecule en route to its folded state has so far been realized only in silico. We have used single-molecule force spectroscopy to study the folding transitions of single calmodulin molecules. High-resolution optical tweezers assays in combination with hidden Markov analysis reveal a complex network of on- and off-pathway intermediates. Cooperative and anticooperative interactions across domain boundaries can be observed directly. The folding network involves four intermediates. Two off-pathway intermediates exhibit non-native interdomain interactions and compete with the ultrafast productive folding pathway.

1 Physik Department E22, Technische Universität München, James-Franck-Strasse, 85748 Garching, Germany.
2 Munich Center for Integrated Protein Science, 81377 München, Germany.

* Present address: Chemistry and Chemical Biology, Harvard University, 12 Oxford Street, Cambridge, MA 02138, USA.

{dagger} To whom correspondence should be addressed. E-mail: mrief{at}

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