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Spectroscopic and DFT studies of second-sphere variants of the type 1 copper site in azurin: covalent and nonlocal electrostatic contributions to reduction potentials

Hadt, Ryan G. and Sun, Ning and Marshall, Nicholas M. and Hodgson, Keith O. and Hedman, Britt and Lu, Yi and Solomon, Edward I. (2012) Spectroscopic and DFT studies of second-sphere variants of the type 1 copper site in azurin: covalent and nonlocal electrostatic contributions to reduction potentials. Journal of the American Chemical Society, 134 (40). pp. 16701-16716. ISSN 0002-7863. PMCID PMC3506006. doi:10.1021/ja306438n.

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The reduction potentials (E^0) of type 1 (T1) or blue copper (BC) sites in proteins and enzymes with identical first coordination spheres around the redox active copper ion can vary by ~400 mV. Here, we use a combination of low-temperature electronic absorption and magnetic circular dichroism, electron paramagnetic resonance, resonance Raman, and S K-edge X-ray absorption spectroscopies to investigate a series of second-sphere variants--F114P, N47S, and F114N in Pseudomonas aeruginosa azurin--which modulate hydrogen bonding to and protein-derived dipoles nearby the Cu-S(Cys) bond. Density functional theory calculations correlated to the experimental data allow for the fractionation of the contributions to tuning E(0) into covalent and nonlocal electrostatic components. These are found to be significant, comparable in magnitude, and additive for active H-bonds, while passive H-bonds are mostly nonlocal electrostatic in nature. For dipoles, these terms can be additive to or oppose one another. This study provides a methodology for uncoupling covalency from nonlocal electrostatics, which, when coupled to X-ray crystallographic data, distinguishes specific local interactions from more long-range protein/active interactions, while affording further insight into the second-sphere mechanisms available to the protein to tune the E^0 of electron-transfer sites in biology.

Item Type:Article
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URLURL TypeDescription CentralArticle Information
Hadt, Ryan G.0000-0001-6026-1358
Lu, Yi0000-0003-1221-6709
Solomon, Edward I.0000-0003-0291-3199
Additional Information:© 2012 American Chemical Society. Received: July 7, 2012. Published: September 18, 2012. This work was supported by grants NSF CHE-0948211 (E.I.S.), NIH DK-31450 (E.I.S.), NIH RR-001209 (K.O.H.), NSF CHE-1058959 (Y.L). The SSRL Structural Molecular Biology program is supported by the Department of Energy, Office of Biological and Environmental Research, and by the National Institutes of Health, National Institute of General Medical Sciences (including P41GM103393), and the National Center for Research Resources (P41RR001209). R.G.H. acknowledges a Gerhard Casper Stanford Graduate Fellowship. We thank Yang Ha for help analyzing the S K-edge XAS data. The authors declare no competing financial interest.
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Department of Energy (DOE)UNSPECIFIED
Stanford UniversityUNSPECIFIED
Issue or Number:40
PubMed Central ID:PMC3506006
Record Number:CaltechAUTHORS:20180612-125943278
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Official Citation:Spectroscopic and DFT Studies of Second-Sphere Variants of the Type 1 Copper Site in Azurin: Covalent and Nonlocal Electrostatic Contributions to Reduction Potentials Ryan G. Hadt, Ning Sun, Nicholas M. Marshall, Keith O. Hodgson, Britt Hedman, Yi Lu, and Edward I. Solomon Journal of the American Chemical Society 2012 134 (40), 16701-16716 DOI: 10.1021/ja306438n
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:87011
Deposited By: George Porter
Deposited On:12 Jun 2018 20:21
Last Modified:15 Nov 2021 20:44

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