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Research Article

Strong reversible Fe3+-mediated bridging between dopa-containing protein films in water

Hongbo Zeng, Dong Soo Hwang, Jacob N. Israelachvili, and J. Herbert Waite
  1. aDepartment of Chemical and Materials Engineering, University of Alberta, Edmonton, AB, T6G 2V4 Canada; and
  2. bDepartment of Chemical Engineering,
  3. cMaterials Research Laboratory, and
  4. dDepartment of Molecular, Cell and Developmental Biology, University of California, Santa Barbara, CA 93106

See allHide authors and affiliations

PNAS first published July 6, 2010; https://doi.org/10.1073/pnas.1007416107
Hongbo Zeng
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  • For correspondence: hongbo.zeng@ualberta.ca waite@lifesci.ucsb.edu jacob@engineering.ucsb.edu
Dong Soo Hwang
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Jacob N. Israelachvili
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  • For correspondence: hongbo.zeng@ualberta.ca waite@lifesci.ucsb.edu jacob@engineering.ucsb.edu
J. Herbert Waite
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  • For correspondence: hongbo.zeng@ualberta.ca waite@lifesci.ucsb.edu jacob@engineering.ucsb.edu
  1. Contributed by Jacob N. Israelachvili, June 1, 2010 (sent for review February 10, 2010)

  2. ↵1H.Z. and D.S.H. contributed equally to this work.

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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 Fe3+ 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 ∼ 10) and didn’t show any cohesive tendencies in previous surface forces apparatus (SFA) studies. Here, we show that Fe3+ ions can mediate unusually strong interactions between the positively charged proteins. Using an SFA, Fe3+ was observed to impart robust bridging (Wad ≈ 4.3 mJ/m2) between two noninteracting mfp-1 films in aqueous buffer approaching the ionic strength of seawater. The Fe3+ bridging between the mfp-1-coated surfaces is fully reversible in water, increasing with contact time and iron concentration up to 10 μM; at 100 μM, Fe3+ bridging adhesion is abolished. Bridging is apparently due to the formation of multivalent dopa-iron complexes. Similar Fe-mediated bridging (Wad ≈ 5.7 mJ/m2) 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.

  • byssus
  • metal coordination
  • tris-catecholato-iron (III) complex

Footnotes

  • 2To whom correspondence may be addressed. E-mail: hongbo.zeng{at}ualberta.ca, waite{at}lifesci.ucsb.edu, or jacob{at}engineering.ucsb.edu.
  • Author contributions: H.Z., D.S.H., J.N.I., and J.H.W. designed research; H.Z. and D.S.H. performed research; J.N.I. and J.H.W. contributed new reagents/analytic tools; H.Z. and D.S.H. analyzed data; and H.Z., D.S.H., J.N.I., and J.H.W. wrote the paper.

  • The authors declare no conflict of interest.

  • This article contains supporting information online at www.pnas.org/lookup/suppl/doi:10.1073/pnas.1007416107/-/DCSupplemental.

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    Strong reversible Fe3+-mediated bridging between dopa-containing protein films in water
    Hongbo Zeng, Dong Soo Hwang, Jacob N. Israelachvili, J. Herbert Waite
    Proceedings of the National Academy of Sciences Jul 2010, DOI: 10.1073/pnas.1007416107

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    Strong reversible Fe3+-mediated bridging between dopa-containing protein films in water
    Hongbo Zeng, Dong Soo Hwang, Jacob N. Israelachvili, J. Herbert Waite
    Proceedings of the National Academy of Sciences Jul 2010, DOI: 10.1073/pnas.1007416107
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