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EMBO reports 6, 1, 46–51 (2005)
doi:10.1038/sj.embor.7400317
Published online: 17 December 2004
The folding pathway of a fast-folding immunoglobulin domain revealed by single-molecule mechanical experiments
Ingo Schwaiger1, Michael Schleicher2, Angelika A Noegel3 & Matthias Rief1
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1 Physik-Department E22, TU-München, James-Franck-Strasse, 85747 Garching, Germany
2 Adolf-Butenandt-Inst./Zellbiologie, Ludwig-Maximilians-Universität München, Schillerstrasse 42, 80336 München, Germany
3 Institut für Biochemie I, Med. Fakultät der Universität zu Köln, Joseph-Stelzmann-Strasse 52, 50931 Köln, Germany
To whom correspondence should be addressed
Matthias Rief Tel: +49 28 91 2472; Fax: +49 28 91 2523; E-mail: mrief@ph.tum.de
Received 22 September 2004; Accepted 19 November 2004; Published online 17 December 2004.
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Abstract
The F-actin crosslinker filamin from Dictyostelium discoideum (ddFLN) has a rod domain consisting of six structurally similar immunoglobulin domains. When subjected to a stretching force, domain 4 unfolds at a lower force than all the other domains in the chain. Moreover, this domain shows a stable intermediate along its mechanical unfolding pathway. We have developed a mechanical single-molecule analogue to a double-jump stopped-flow experiment to investigate the folding kinetics and pathway of this domain. We show that an obligatory and productive intermediate also occurs on the folding pathway of the domain. Identical mechanical properties suggest that the unfolding and refolding intermediates are closely related. The folding process can be divided into two consecutive steps: in the first step 60 C-terminal amino acids form an intermediate at the rate of 55 s-1; and in the second step the remaining 40 amino acids are packed on this core at the rate of 179 s-1. This division increases the overall folding rate of this domain by a factor of ten compared with all other homologous domains of ddFLN that lack the folding intermediate.
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