Electrostatic Docking of a Supramolecular Host−Guest Assembly to Cytochrome c Probed by Bidirectional Photoinduced Electron Transfer

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Abstract

A water-soluble octacarboxyhemicarcerand was used as a shuttle to transport redox-active substrates across the aqueous medium and deliver them to the target protein. The results show that weak multivalent interactions and conformational flexibility can be exploited to reversibly bind complex supramolecular assemblies to biological molecules. Hydrophobic electron donors and acceptors were encapsulated within the hemicarcerand, and photoinduced electron transfer (ET) between the Zn-substituted cytochrome c (MW = 12.3 kD) and the host−guest complexes (MW = 2.2 kD) was used to probe the association between the negatively charged hemicarceplex and the positively charged protein. The behavior of the resulting ternary protein−hemicarcerand−guest assembly was investigated in two binding limits: (1) when K_encaps K_assoc, the hemicarcerand transports the ligand to the protein while protecting it from the aqueous medium; and (2) when K_assoc > K_encaps, the hemicarcerand−protein complex is formed first, and the hemicarcerand acts as an artificial receptor site that intercepts ligands from solution and positions them close to the active site of the metalloenzyme. In both cases, ET mediated by the protein-bound hemicarcerand is much faster than that due to diffusional encounters with the respective free donor or acceptor in solution. The measured ET rates suggest that the dominant binding region of the host−guest complex on the surface of the protein is consistent with the docking area of the native redox partner of cytochrome c. The strong association with the protein is attributed to the flexible conformation and adaptable charge distribution of the hemicarcerand, which allow for surface-matching with the cytochrome.

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This article has been cited by 2 ACS Journal articles (2 most recent appear below).

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  Zinc-Substituted Cytochrome P450_cam: Characterization of Protein Conformers F420 and F450 by Photoinduced Electron Transfer

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  Biochemistry2012 51 (7), 1431-1438

  • Zinc-Substituted Cytochrome P450_cam: Characterization of Protein Conformers F420 and F450 by Photoinduced Electron Transfer

    Katarzyna I. Jankowska, Cynthia V. Pagba, and Piotr Piotrowiak
    Biochemistry2012 51 (7), 1431-1438

    Metal substitution of heme proteins is widely applied in the study of biologically relevant electron transfer (ET) reactions. It has been shown that many modified proteins remain in their native conformation and can provide useful insights into the ...

    Abstract | Full Text HTML | Hi-Res PDF | PDF w/ Links
• 

  The Reorganization Energy in Cytochrome c is Controlled by the Accessibility of the Heme to the Solvent

  Carlo Augusto Bortolotti, Magdalena E. Siwko, Elena Castellini, Antonio Ranieri, Marco Sola, and Stefano Corni
  The Journal of Physical Chemistry Letters2011 2 (14), 1761-1765

  • The Reorganization Energy in Cytochrome c is Controlled by the Accessibility of the Heme to the Solvent

    Carlo Augusto Bortolotti, Magdalena E. Siwko, Elena Castellini, Antonio Ranieri, Marco Sola, and Stefano Corni
    The Journal of Physical Chemistry Letters2011 2 (14), 1761-1765

    Elucidation of the molecular determinants of the reorganization energy λ is central to the understanding of fundamental biological processes based on energy transduction pathways. Here, we use a combined experimental/theoretical approach to ...

    Abstract | Full Text HTML | Hi-Res PDF | PDF w/ Links

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