title: Analysis and Control of Chain Mobility in Protein Hydrogels.
abstract: Coiled-coil domains can direct the assembly of protein block copolymers into physically cross-linked, viscoelastic hydrogels. Here, we describe the use of fluorescence recovery after photobleaching (FRAP) to probe chain mobility in reversible hydrogels assembled from engineered proteins bearing terminal coiled-coil domains. We show that chain mobility can be related to the underlying dynamics of the coiled-coil domains by application of a three-state "hopping" model of chain migration. We further show that genetic programming allows the effective mobility of network chains to be varied 500-fold through modest changes in protein sequence. Destabilization of the coiled-coil domains by site-directed mutagenesis increases the effective diffusivity of probe chains. Conversely, probe mobility is reduced by expanding the hydrophobic surface area of the coiled-coil domains through introduction of the bulky leucine surrogate homoisoleucine. Predictions from the three-state model imply asymmetric sequential binding of the terminal domains. Brownian Dynamics simulations suggest that binding asymmetry is a general feature of reversible gels, arising from a loss in entropy as chains transition to a conformationally restricted bridged state.
authors.affiliation: Division of Chemistry and Chemical Engineering, California Institute of Technology , 1200 East California Boulevard, MC 210-41, Pasadena, California 91125, United States.
authors.forename: Peter B
authors.identifier: 0000-0002-9586-2126
authors.initials: PB
authors.lastname: Rapp
authors.affiliation: Division of Chemistry and Chemical Engineering, California Institute of Technology , 1200 East California Boulevard, MC 210-41, Pasadena, California 91125, United States.
authors.forename: Ahmad K
authors.initials: AK
authors.lastname: Omar
authors.affiliation: Division of Chemistry and Chemical Engineering, California Institute of Technology , 1200 East California Boulevard, MC 210-41, Pasadena, California 91125, United States.
authors.forename: Jeff J
authors.initials: JJ
authors.lastname: Shen
authors.affiliation: Division of Chemistry and Chemical Engineering, California Institute of Technology , 1200 East California Boulevard, MC 210-41, Pasadena, California 91125, United States.
authors.forename: Maren E
authors.initials: ME
authors.lastname: Buck
authors.affiliation: Division of Chemistry and Chemical Engineering, California Institute of Technology , 1200 East California Boulevard, MC 210-41, Pasadena, California 91125, United States.
authors.forename: Zhen-Gang
authors.identifier: 0000-0002-3361-6114
authors.initials: ZG
authors.lastname: Wang
authors.affiliation: Division of Chemistry and Chemical Engineering, California Institute of Technology , 1200 East California Boulevard, MC 210-41, Pasadena, California 91125, United States.
authors.forename: David A
authors.initials: DA
authors.lastname: Tirrell
mesh_terms: D005453:Fluorescence; D020100:Hydrogels / Q000737:chemistry*; D057927:Hydrophobic and Hydrophilic Interactions; D056004:Molecular Dynamics Simulation; D016297:Mutagenesis, Site-Directed; D015202:Protein Engineering; D011506:Proteins / Q000737:chemistry* / Q000235:genetics; D013499:Surface Properties
chemical_list: D020100:Hydrogels; D011506:Proteins