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Structure and mechanical properties of artificial protein hydrogels assembled through aggregation of leucine zipper peptide domains

Shen, Wei and Kornfield, Julia A. and Tirrell, David A. (2007) Structure and mechanical properties of artificial protein hydrogels assembled through aggregation of leucine zipper peptide domains. Soft Matter, 3 (1). pp. 99-107. ISSN 1744-6848. doi:10.1039/b610986a.

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Artificial protein hydrogels made from a triblock protein (designated AC10A, where A is an acidic zipper domain and C10 comprises 10 repeats of the nonapeptide sequence exhibit normalized plateau storage moduli (G/nkT) less than 0.13 at all concentrations, pH values, and ionic strengths examined. These gels are surprisingly soft due to loop formation at the expense of bridges between physical junctions. Molecular-level evidence of loop formation is provided by strong fluorescence energy transfer (FRET) between distinct chromophores placed at the C- and N-termini of labelled chains diluted in an excess of unlabelled chains. The tendency to form loops originates from the compact size of the random coil midblock (mean RH(C10) 20 Å, determined from quasi-elastic light scattering of C10), and is facilitated by the ability of the leucine zipper domains to form antiparallel aggregates. Although the aggregation number of the leucine zipper domains is small (tetrameric, determined from multi-angle static light scattering of AC10 diblock), the average center-to-center distance between aggregates is roughly 1.5 times the average end-to-end distance of the C10 domain in a 7% w/v network. To avoid stretching the C10 domain, the chains tend to form loops. Changes in pH or ionic strength that expand the polyelectrolyte midblock favor bridging, leading to greater G as long as leucine zipper endblocks do not dissociate. Understanding of the network structure provided successful design strategies to increase the rigidity of these hydrogels. In contrast to intuitive design concepts for rubber and gel materials, it was shown that increasing either the length or the charge density of the midblock increases rigidity, because fewer chains are wasted in loop formation.

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Kornfield, Julia A.0000-0001-6746-8634
Tirrell, David A.0000-0003-3175-4596
Additional Information:This journal is © The Royal Society of Chemistry 2007. Received 31st July 2006, Accepted 20th October 2006. First published on the web 9th November 2006. The authors acknowledge the NSF Center for the Science and Engineering of Materials for financial support.
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Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:8568
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Deposited On:20 Aug 2007
Last Modified:08 Nov 2021 20:51

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