The study of long-range ET has attained a central role in modern chemistry through the development of (i) linked donor-acceptor model compounds; (ii) redox-modified proteins; and, the focus of our research, (iii) modified protein-protein complexes. Our program addresses the two fundamental and complementary questions underlying the critical process of inter-protein electron-transfer (ET), through studies of three experimental systems: What are the structural and dynamical features that control interfacial recognition and docking between ET partners? What are the structural, dynamical, and energetic features that control the actual electron-transfer event within the protein-protein complex? Mixed-metal hemoglobin (Hb) hybrids provide an unmatched opportunity to study the ET event within a 'pre-docked' complex, across a crystallographically defined, experimentally manipulable protein-protein (inter-subunit) interface. Cytochrome c Peroxidase (CcP) is the paradigm of a protein with multiple, interacting redox centers and multiple binding domains for reacting with its ET partner, cytochrome c (Cc). The physiologically important ET complexes of cytochrome b5 (b5) with myoglobin (Mb) and Hb present complementary issues: The [Mb, b5] system of low molecular weight partners raises fundamental issues of interfacial recognition and docking; the [Hb, b5] pair offers the opportunity to probe the coupling of ET to quaternary assembly and conformation of a multi-subunit protein.
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