Complex stability of single proteins explored by forced unfolding experiments

Harald Janovjak, K. Tanuj Sapra, Daniel J. Müller

Research output: Contribution to journalArticlepeer-review

5 Citations (Scopus)


In the last decade atomic force microscopy has been used to measure the mechanical stability of single proteins. These force spectroscopy experiments have shown that many water-soluble and membrane proteins unfold via one or more intermediates. Recently, Li and co-workers found a linear correlation between the unfolding force of the native state and the intermediate in fibronectin, which they suggested indicated the presence of a molecular memory or multiple unfolding pathways (1). Here, we apply two independent methods in combination with Monte Carlo simulations to analyze the unfolding of α-helices E and D of bacteriorhodopsin (BR). We show that correlation analysis of unfolding forces is very sensitive to errors in force calibration of the instrument. In contrast, a comparison of relative forces provides a robust measure for the stability of unfolding intermediates. The proposed approach detects three energetically different states of α-helices E and D in trimeric BR. These states are not observed for monomeric BR and indicate that substantial information is hidden in forced unfolding experiments of single proteins.

Original languageEnglish
Pages (from-to)L37-L39
JournalBiophysical Journal
Issue number5
Publication statusPublished - 1 May 2005
Externally publishedYes


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