title: Mimicking protein-protein electron transfer: voltammetry of Pseudomonas aeruginosa azurin and the Thermus thermophilus Cu(A) domain at omega-derivatized self-assembled-monolayer gold electrodes.
abstract: Well-defined voltammetric responses of redox proteins with acidic-to-neutral pI values have been obtained on pure alkanethiol as well as on mixed self-assembled-monolayer (SAM) omega-derivatized alkanethiol/gold bead electrodes. Both azurin (P. aeruginosa) (pI = 5.6) and subunit II (Cu(A) domain) of ba(3)-type cytochrome c oxidase (T. thermophilus) (pI = 6.0) exhibit optimal voltammetric responses on 1:1 mixtures of [H(3)C(CH(2))(n)()SH + HO(CH(2))(n)()SH] SAMs. The electron transfer (ET) rate vs distance behavior of azurin and Cu(A) is independent of the omega-derivatized alkanethiol SAM headgroups. Strikingly, only wild-type azurin and mutants containing Trp48 give voltammetric responses: based on modeling, we suggest that electronic coupling with the SAM headgroup (H(3)C- and/or HO-) occurs at the Asn47 side chain carbonyl oxygen and that an Asn47-Cys112 hydrogen bond promotes intramolecular ET to the copper. Inspection of models also indicates that the Cu(A) domain of ba(3)-type cytochrome c oxidase is coupled to the SAM headgroup (H(3)C- and/or HO-) near the main chain carbonyl oxygen of Cys153 and that Phe88 (analogous to Trp143 in subunit II of cytochrome c oxidase from R. sphaeroides) is not involved in the dominant tunneling pathway. Our work suggests that hydrogen bonds from hydroxyl or other proton-donor groups to carbonyl oxygens potentially can facilitate intermolecular ET between physiological redox partners.
authors.affiliation: Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, California 91125, USA.
authors.forename: Kyoko
authors.initials: K
authors.lastname: Fujita
authors.forename: Nobufumi
authors.initials: N
authors.lastname: Nakamura
authors.forename: Hiroyuki
authors.initials: H
authors.lastname: Ohno
authors.forename: Brian S
authors.initials: BS
authors.lastname: Leigh
authors.forename: Katsumi
authors.initials: K
authors.lastname: Niki
authors.forename: Harry B
authors.initials: HB
authors.lastname: Gray
authors.forename: John H
authors.initials: JH
authors.lastname: Richards
mesh_terms: D001400:Azurin / Q000737:chemistry* / Q000378:metabolism; D040761:Biomimetic Materials / Q000737:chemistry / Q000378:metabolism; D004563:Electrochemistry; D004566:Electrodes; D003576:Electron Transport Complex IV / Q000737:chemistry* / Q000378:metabolism; D006046:Gold; D007700:Kinetics; D008958:Models, Molecular; D016297:Mutagenesis, Site-Directed; D017434:Protein Structure, Tertiary; D011550:Pseudomonas aeruginosa / Q000737:chemistry* / Q000378:metabolism; D016963:Thermus thermophilus / Q000201:enzymology*
chemical_list: D001400:Azurin; D006046:Gold; C117108:cytochrome C oxidase subunit II; D003576:Electron Transport Complex IV