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.
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.
Fujita
Kyoko
K
Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, California 91125, USA.
Nakamura
Nobufumi
N
Ohno
Hiroyuki
H
Leigh
Brian S
BS
Niki
Katsumi
K
Gray
Harry B
HB
Richards
John H
JH
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*
D001400:Azurin; D006046:Gold; C117108:cytochrome C oxidase subunit II; D003576:Electron Transport Complex IV