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Issue 1, 2007
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Structure and mechanical properties of artificial protein hydrogels assembled through aggregation of leucine zipper peptide domains

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Abstract

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 Image ID:b610986a-u1.gif 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.

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

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Publication details

The article was received on 31 Jul 2006, accepted on 20 Oct 2006 and first published on 09 Nov 2006


Article type: Paper
DOI: 10.1039/B610986A
Soft Matter, 2007,3, 99-107

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

    W. Shen, J. A. Kornfield and D. A. Tirrell, Soft Matter, 2007, 3, 99
    DOI: 10.1039/B610986A

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