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Published online on April 29, 2008, 10.1073/pnas.0709246105
PNAS | May 6, 2008 | vol. 105 | no. 18 | 6590-6595


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From the Cover
BIOLOGICAL SCIENCES / BIOPHYSICS
Assembly mechanism of recombinant spider silk proteins

S. Rammensee*, U. Slotta{dagger},{ddagger}, T. Scheibel{dagger},{ddagger},§, and A. R. Bausch*,§

*E27-Biophysics, Physics Department, James Franck Straße, and {dagger}Biotechnology, Chemistry Department, Lichtenbergstraße 4, Technische Universität München, 85747 Garching, Germany

Edited by David Baker, University of Washington, Seattle, WA, and approved March 13, 2008 (received for review October 5, 2007)

Spider silk threads are formed by the irreversible aggregation of silk proteins in a spinning duct with dimensions of only a few micrometers. Here, we present a microfluidic device in which engineered and recombinantly produced spider dragline silk proteins eADF3 (engineered Araneus diadematus fibroin) and eADF4 are assembled into fibers. Our approach allows the direct observation and identification of the essential parameters of dragline silk assembly. Changes in ionic conditions and pH result in aggregation of the two proteins. Assembly of eADF3 fibers was induced only in the presence of an elongational flow component. Strikingly, eADF4 formed fibers only in combination with eADF3. On the basis of these results, we propose a model for dragline silk aggregation and early steps of fiber assembly in the microscopic regime.

colloids | microfluidics | protein materials | rheology

Author contributions: T.S. and A.R.B. designed research; S.R. and U.S. performed research; U.S. contributed new reagents/analytic tools; S.R. analyzed data; and S.R., T.S., and A.R.B. wrote the paper.

{ddagger}Present address: Biomaterials, Fakultät für Angewandte Naturwissenschaften, Universitätsstraße 30, Universität Bayreuth, 95440 Bayreuth, Germany.

The authors declare no conflict of interest.

This article is a PNAS Direct Submission.

This article contains supporting information online at www.pnas.org/cgi/content/full/0709246105/DCSupplemental.

The elongational flow component is estimated from the averaged flow speed of vx of 5 mm/s in the channels and of 160 mm/s in the narrow orifice. The distance between orifice and the onset of elongational flow is approximately 100 µm.

§To whom correspondence may be addressed. E-mail: abausch{at}ph.tum.de or thomas.scheibel{at}uni-bayreuth.de

© 2008 by The National Academy of Sciences of the USA


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