Protein-protein electron transfer (ET) occupies a central place in biology and chemistry. Beyond this, the underlying phenomena of protein-protein recognition and docking, which are central to almost all biological processes, are particularly amenable to study through measurements of inter-protein ET, whose steep dependence on distance/pathways acts as a unique 'filter'for probing reactive configurations in the presence of more numerous non-reactive ones. Our results indicate that (a) ET across a protein-protein interface typically is modulated by conformational conversion between and within ensembles of states with different interface structures and degrees of surface hydration, (b) ET photocycles in conformationally mobile systems provide 'clocks'against which such dynamic processes can be measured, and (c) the photocycle clocks can be used to characterize the coupling of conformation to function over timescales from picoseconds to seconds. The goal of understanding protein-protein interactions and interprotein ET has led us to recent, highly successful efforts at their control through a charge-reversal strategy for redesign of the docking interface, one result being the discovery of an interprotein singlet ET photocycle on ps-ns timescales. We propose: (i) to refine the interface redesign strategy, to apply it to new partners, and to use it to discover new systems with singlet ET photocycles;(ii) to examine conformationally-modulated ET through a tightly integrated program comprised of kinetic measurements of the variations of ET with solvent, structural characterization of dynamic complexes (NMR), and computational (Brownian Dynamics/MD/Smoluchowski equation) approaches. The three systems to be studied involve distinct interfaces: myoglobin (Mb), the vehicle for protein redesign efforts, binds to electron acceptor partner proteins primarily through electrostatic interactions;the structurally characterized complex between cytochrome c peroxidase (CcP) and cytochrome c (Cc) is primarily bound by hydrophobic interactions;[Zn;Fe] hemoglobin (Hb) hybrids exhibit a mixture of interactions at the interface between the ET- partner chains. We will test the hypothesis that, as a result, each system exhibits a distinct combination of three types of conformational control of ET: dynamic processes, conversion among conformations with different degrees of surface hydration, and/or changes in volume. We also propose to 'translate'the understanding derived from these studies to the problem of nucleotide-regulated, conformationally-linked ET in catalysis by nitrogenase.

Public Health Relevance

Electron transfer between proteins is vital to the physiological processes of respiration and metabolism. Beyond this, the underlying phenomena of protein-protein recognition and docking are central to almost all biological processes that underlie human physiology and health. Our research program addresses fundamental questions of interprotein electron transfer, how it is modulated by atomic motions at the protein-protein interface, and how it might be controlled by protein redesign. It translates these findings into the realm of catalysis by the enzyme, nitrogenase.

Agency
National Institute of Health (NIH)
Institute
National Heart, Lung, and Blood Institute (NHLBI)
Type
Research Project (R01)
Project #
5R01HL063203-16
Application #
8616391
Study Section
Special Emphasis Panel (ZRG1-BCMB-B (02))
Program Officer
Qasba, Pankaj
Project Start
1999-03-15
Project End
2017-01-31
Budget Start
2014-02-01
Budget End
2015-01-31
Support Year
16
Fiscal Year
2014
Total Cost
$301,636
Indirect Cost
$96,624
Name
Northwestern University at Chicago
Department
Chemistry
Type
Schools of Arts and Sciences
DUNS #
160079455
City
Evanston
State
IL
Country
United States
Zip Code
60201
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Trana, Ethan N; Nocek, Judith M; Woude, Jon Vander et al. (2016) Charge-Disproportionation Symmetry Breaking Creates a Heterodimeric Myoglobin Complex with Enhanced Affinity and Rapid Intracomplex Electron Transfer. J Am Chem Soc 138:12615-28
Danyal, Karamatullah; Shaw, Sudipta; Page, Taylor R et al. (2016) Negative cooperativity in the nitrogenase Fe protein electron delivery cycle. Proc Natl Acad Sci U S A 113:E5783-E5791
Page, Taylor R; Hoffman, Brian M (2015) Control of cyclic photoinitiated electron transfer between cytochrome c peroxidase (W191F) and cytochrome c by formation of dynamic binary and ternary complexes. Biochemistry 54:1188-97
Co, Nadia Petlakh; Young, Ryan M; Smeigh, Amanda L et al. (2014) Symmetrized photoinitiated electron flow within the [myoglobin:cytochrome bâ‚…] complex on singlet and triplet time scales: energetics vs dynamics. J Am Chem Soc 136:12730-6
Duval, Simon; Danyal, Karamatullah; Shaw, Sudipta et al. (2013) Electron transfer precedes ATP hydrolysis during nitrogenase catalysis. Proc Natl Acad Sci U S A 110:16414-9
Jiang, Nan; Kuznetsov, Aleksey; Nocek, Judith M et al. (2013) Distance-independent charge recombination kinetics in cytochrome c-cytochrome c peroxidase complexes: compensating changes in the electronic coupling and reorganization energies. J Phys Chem B 117:9129-41
Mayweather, Diana; Danyal, Karamatullah; Dean, Dennis R et al. (2012) Correction to temperature invariance of the nitrogenase electron transfer mechanism. Biochemistry 51:9027
Seefeldt, Lance C; Hoffman, Brian M; Dean, Dennis R (2012) Electron transfer in nitrogenase catalysis. Curr Opin Chem Biol 16:19-25

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