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Related Experiment Video

Updated: May 28, 2026

Pull-down of Calmodulin-binding Proteins

Pull-down of Calmodulin-binding Proteins

Published on: January 23, 2012

The complex folding network of single calmodulin molecules.

Johannes Stigler¹, Fabian Ziegler, Anja Gieseke

¹Physik Department E22, Technische Universität München, James-Franck-Strasse, 85748 Garching, Germany.

Science (New York, N.Y.)

|October 29, 2011

Summary

Researchers directly observed protein folding pathways using single-molecule force spectroscopy. This revealed complex intermediate states and interactions during calmodulin folding, offering new insights into protein dynamics.

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Area of Science:

Biophysics
Molecular Biology
Protein Dynamics

Background:

Observing protein folding in real-time at the single-molecule level has been a significant challenge.
Previous studies relied heavily on computational simulations (in silico) for detailed conformational analysis.

Purpose of the Study:

To directly observe and characterize the folding transitions of single calmodulin molecules.
To investigate the network of intermediates and interactions during the protein folding process.

Main Methods:

Employed single-molecule force spectroscopy utilizing high-resolution optical tweezers.
Applied hidden Markov analysis to interpret the complex data from force spectroscopy.

Main Results:

Revealed a complex network of on- and off-pathway intermediates during calmodulin folding.
Directly observed cooperative and anticooperative interactions between protein domains.
Identified four key intermediates, including two off-pathway states with non-native interactions.

Conclusions:

Single-molecule force spectroscopy provides unprecedented direct observation of protein folding pathways.
The folding of calmodulin involves a complex network of intermediates that compete with the productive folding route.