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Published November 3, 2004 | public
Journal Article

Mimicking protein-protein electron transfer: voltammetry of Pseudomonas aeruginosa azurin and the Thermus thermophilus Cu_A domain at ω-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) ω-derivatized alkanethiol/gold bead electrodes. Both azurin (P. aeruginosa) (pI = 5.6) and subunit II (CuA domain) of ba_3-type cytochrome c oxidase (T. thermophilus) (pI = 6.0) exhibit optimal voltammetric responses on 1:1 mixtures of [H_3C(CH_2)_nSH + HO(CH_2)_nSH] SAMs. The electron transfer (ET) rate vs distance behavior of azurin and CuA is independent of the ω-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_3C− 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 CuA domain of ba3-type cytochrome c oxidase is coupled to the SAM headgroup (H_3C− 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.

Additional Information

© 2004 American Chemical Society. Received April 13, 2004. Publication Date (Web): October 7, 2004. Dedicated to the memory of Katsumi Niki, who passed away on 4 May 2004, a few weeks after our manuscript was submitted. This work was supported by NIH DK19038, NSF, and the Arnold and Mabel Beckman Foundation. K.F. thanks the Japan Society for Promotion of Science (Research Fellowship for Young Scientists) for support; B.S.L. acknowledges the Parsons Foundation for a graduate fellowship.

Additional details

Created:
August 19, 2023
Modified:
October 23, 2023