title: Bioelectrocatalytic hydrogels from electron-conducting metallopolypeptides coassembled with bifunctional enzymatic building blocks.
abstract: Here, we present two bifunctional protein building blocks that coassemble to form a bioelectrocatalytic hydrogel that catalyzes the reduction of dioxygen to water. One building block, a metallopolypeptide based on a previously designed triblock polypeptide, is electron-conducting. A second building block is a chimera of artificial alpha-helical leucine zipper and random coil domains fused to a polyphenol oxidase, small laccase (SLAC). The metallopolypeptide has a helix-random-helix secondary structure and forms a hydrogel via tetrameric coiled coils. The helical and random domains are identical to those fused to the polyphenol oxidase. Electron-conducting functionality is derived from the divalent attachment of an osmium bis-bipyrdine complex to histidine residues within the peptide. Attachment of the osmium moiety is demonstrated by mass spectroscopy (MS-MALDI-TOF) and cyclic voltammetry. The structure and function of the alpha-helical domains are confirmed by circular dichroism spectroscopy and by rheological measurements. The metallopolypeptide shows the ability to make electrical contact to a solid-state electrode and to the redox centers of modified SLAC. Neat samples of the modified SLAC form hydrogels, indicating that the fused alpha-helical domain functions as a physical cross-linker. The fusion does not disrupt dimer formation, a necessity for catalytic activity. Mixtures of the two building blocks coassemble to form a continuous supramolecular hydrogel that, when polarized, generates a catalytic current in the presence of oxygen. The specific application of the system is a biofuel cell cathode, but this protein-engineering approach to advanced functional hydrogel design is general and broadly applicable to biocatalytic, biosensing, and tissue-engineering applications.
authors.affiliation: Department of Chemical Engineering, Columbia University, 500 West 120th Street, New York, NY 10027, USA.
authors.forename: Ian R
authors.initials: IR
authors.lastname: Wheeldon
authors.forename: Joshua W
authors.initials: JW
authors.lastname: Gallaway
authors.forename: Scott Calabrese
authors.initials: SC
authors.lastname: Barton
authors.forename: Scott
authors.initials: S
authors.lastname: Banta
mesh_terms: D000595:Amino Acid Sequence; D002384:Catalysis; D004156:Catechol Oxidase / Q000737:chemistry; D004583:Electrons; D020100:Hydrogels / Q000737:chemistry*; D042845:Laccase / Q000737:chemistry; D013058:Mass Spectrometry; D008969:Molecular Sequence Data; D017892:Osmium Compounds / Q000737:chemistry; D010084:Oxidation-Reduction; D010100:Oxygen / Q000737:chemistry; D010455:Peptides / Q000737:chemistry*; D015202:Protein Engineering; D017433:Protein Structure, Secondary; D013329:Structure-Activity Relationship; D014867:Water / Q000737:chemistry
chemical_list: D020100:Hydrogels; D017892:Osmium Compounds; D010455:Peptides; D014867:Water; D004156:Catechol Oxidase; D042845:Laccase; D010100:Oxygen