Article

Investigation of the Low Frequency Dynamics of Heme Proteins: Native and Mutant Cytochrome P450cam and Redox Partner Complexes

Department of Physics and Center for Interdisciplinary Research on Complex Systems, Northeastern University, Boston, Massachusetts 02115, United States
Department of Biochemistry, University of Illinois, Urbana, Illinois 61801, United States
J. Phys. Chem. B, 2011, 115 (18), pp 5665–5677
DOI: 10.1021/jp112298y
Publication Date (Web): March 10, 2011
Copyright © 2011 American Chemical Society
This article is part of the Shaul Mukamel Festschrift special issue.

Abstract

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Vibrational coherence spectroscopy (VCS) is used to investigate the low-frequency dynamics of camphor-free and camphor-bound cytochrome P450cam (CYP 101) and its L358P mutant. The low-frequency heme vibrations are found to be perturbed upon binding to the electron transfer partner putidaredoxin (Pdx). A strong correlation between the “detuned” vibrational coherence spectrum, which monitors frequencies between 100 and 400 cm−1, and the lower frequency part of the Raman spectrum is also demonstrated. The very low frequency region ≤200 cm−1, uniquely accessed by open-band VCS measurements, reveals a mode near 103 cm−1 in P450cam when camphor is not present in the distal pocket. This reflects the presence of a specific heme distortion, such as saddling or ruffling, in the substrate-free state where water is coordinated to the low-spin iron atom. Such distortions are likely to retard the rate of electron transfer to the substrate-free protein. The presence of strong mode near ∼33 cm−1 in the camphor-bound form suggests a significant heme-doming distortion, which is supported by analysis using normal coordinate structural decomposition. Pdx also displays a strong coherent vibration near 30 cm−1 that in principle could be involved in vibrational resonance with its electron transfer target. A splitting of the 33 cm−1 feature and intensification of a mode near 78 cm−1 appear when the P450cam/Pdx complex is formed. These observations are consistent with vibrational mixing and heme geometric distortions upon Pdx binding that are coincident with the increased thiolate electron donation to the heme. The appearance of a mode near 65 cm−1 in the coherence spectra of the L358P mutant is comparable to the mode at 78 cm−1 seen in the P450cam/Pdx complex and is consistent with the view that the heme and its environment in the L358P mutant are similar to the Pdx-bound native protein. Resonance Raman spectra are presented for both P450cam and the L358P mutant and the changes are correlated with an increased amount of thiolate electron donation to the heme in the mutant sample.

The experimental setup and the procedure for the NSD analysis are presented. This material is available free of charge via the Internet at http://pubs.acs.org.

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Received 27 December 2010
Published online 10 March 2011
Published in print 12 May 2011
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