title: Strong reversible Fe3+-mediated bridging between dopa-containing protein films in water.
abstract: Metal-containing polymer networks are widespread in biology, particularly for load-bearing exoskeletal biomaterials. Mytilus byssal cuticle is an especially interesting case containing moderate levels of Fe(3+) and cuticle protein-mussel foot protein-1 (mfp-1), which has a peculiar combination of high hardness and high extensibility. Mfp-1, containing 13 mol % of dopa (3, 4-dihydroxyphenylalanine) side-chains, is highly positively charged polyelectrolyte (pI approximately 10) and didn't show any cohesive tendencies in previous surface forces apparatus (SFA) studies. Here, we show that Fe(3+) ions can mediate unusually strong interactions between the positively charged proteins. Using an SFA, Fe(3+) was observed to impart robust bridging (W(ad) approximately 4.3 mJ/m(2)) between two noninteracting mfp-1 films in aqueous buffer approaching the ionic strength of seawater. The Fe(3+) bridging between the mfp-1-coated surfaces is fully reversible in water, increasing with contact time and iron concentration up to 10 microM; at 100 microM, Fe(3+) bridging adhesion is abolished. Bridging is apparently due to the formation of multivalent dopa-iron complexes. Similar Fe-mediated bridging (W(ad) approximately 5.7 mJ/m(2)) by a smaller recombinant dopa-containing analogue indicates that bridging is largely independent of molecular weight and posttranslational modifications other than dopa. The results suggest that dopa-metal interactions may provide an energetic new paradigm for engineering strong, self-healing interactions between polymers under water.
authors.affiliation: Department of Chemical and Materials Engineering, University of Alberta, Edmonton, AB, T6G 2V4 Canada. hongbo.zeng@ualberta.ca
authors.forename: Hongbo
authors.initials: H
authors.lastname: Zeng
authors.forename: Dong Soo
authors.initials: DS
authors.lastname: Hwang
authors.forename: Jacob N
authors.initials: JN
authors.lastname: Israelachvili
authors.forename: J Herbert
authors.initials: JH
authors.lastname: Waite
mesh_terms: D000268:Adhesiveness / Q000187:drug effects; D000538:Aluminum Silicates / Q000494:pharmacology; D000818:Animals; D001696:Biomechanical Phenomena / Q000187:drug effects; D004295:Dihydroxyphenylalanine / Q000378:metabolism*; D007501:Iron / Q000494:pharmacology*; D018625:Microscopy, Atomic Force; D049878:Mytilus / Q000378:metabolism; D011506:Proteins / Q000378:metabolism*; D011994:Recombinant Proteins / Q000378:metabolism; D014867:Water / Q000737:chemistry*
chemical_list: D000538:Aluminum Silicates; D011506:Proteins; D011994:Recombinant Proteins; D014867:Water; D004295:Dihydroxyphenylalanine; D007501:Iron; C011934:mica