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RSC Adv. 2014;4(48):25127-25134.

pH-dependent cross-linking of catechols through oxidation via Fe3+ and potential implications for mussel adhesion.

Author information

1
Biomedical Engineering Department, Northwestern University, Evanston, IL 60208 ; Chemistry of Life Processes Institute, Northwestern University, Evanston, IL 60208.
2
Biomedical Engineering Department, Northwestern University, Evanston, IL 60208 ; Chemistry of Life Processes Institute, Northwestern University, Evanston, IL 60208 ; Institute for Bionanotechnology in Medicine, Northwestern University, Evanston, IL 60208.
3
Biomolecular Science and Engineering Program, University of California, Santa Barbara, California 93106, USA.
4
Integrated Molecular Structure Education and Research Center, Northwestern University, Evanston, IL 60208.
5
Biomedical Engineering Department, Northwestern University, Evanston, IL 60208 ; Materials Science and Engineering Department, Northwestern University, Evanston, IL 60208 ; Chemical and Biological Engineering Department, Northwestern University, Evanston, IL 60208 ; Chemistry of Life Processes Institute, Northwestern University, Evanston, IL 60208 ; Institute for Bionanotechnology in Medicine, Northwestern University, Evanston, IL 60208 ; Robert H. Lurie Comprehensive Cancer Center, Northwestern University, Evanston, IL 60208.

Abstract

The mussel byssus is a remarkable attachment structure that is formed by injection molding and rapid in-situ hardening of concentrated solutions of proteins enriched in the catecholic amino acid 3,4-dihydroxy-L-phenylalanine (DOPA). Fe3+, found in high concentrations in the byssus, has been speculated to participate in redox reactions with DOPA that lead to protein polymerization, however direct evidence to support this hypothesis has been lacking. Using small molecule catechols, DOPA-containing peptides, and native mussel foot proteins, we report the first direct observation of catechol oxidation and polymerization accompanied by reduction of Fe3+ to Fe2+. In the case of the small molecule catechol, we identified two dominant dimer species and characterized their connectivities by nuclear magnetic resonance (NMR), with the C6-C6 and C5-C6 linked species as the major and minor products, respectively. For the DOPA-containing peptide, we studied the pH dependence of the reaction and demonstrated that catechol polymerization occurs readily at low pH, but is increasingly diminished in favor of metal-catechol coordination interactions at higher pH. Finally, we demonstrate that Fe3+ can induce cross-links in native byssal mussel proteins mefp-1 and mcfp-1 at acidic pH. Based on these findings, we discuss the potential implications to the chemistry of mussel adhesion.

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