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Biophys J. 2011 Sep 21;101(6):1493-503. doi: 10.1016/j.bpj.2011.08.020. Epub 2011 Sep 20.

Active-site hydration and water diffusion in cytochrome P450cam: a highly dynamic process.

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  • 1Department of Biochemistry and Cellular and Molecular Biology, University of Tennessee-Knoxville, Knoxville, Tennessee, USA.

Abstract

Long-timescale molecular dynamics simulations (300 ns) are performed on both the apo- (i.e., camphor-free) and camphor-bound cytochrome P450cam (CYP101). Water diffusion into and out of the protein active site is observed without biased sampling methods. During the course of the molecular dynamics simulation, an average of 6.4 water molecules is observed in the camphor-binding site of the apo form, compared to zero water molecules in the binding site of the substrate-bound form, in agreement with the number of water molecules observed in crystal structures of the same species. However, as many as 12 water molecules can be present at a given time in the camphor-binding region of the active site in the case of apo-P450cam, revealing a highly dynamic process for hydration of the protein active site, with water molecules exchanging rapidly with the bulk solvent. Water molecules are also found to exchange locations frequently inside the active site, preferentially clustering in regions surrounding the water molecules observed in the crystal structure. Potential-of-mean-force calculations identify thermodynamically favored trans-protein pathways for the diffusion of water molecules between the protein active site and the bulk solvent. Binding of camphor in the active site modifies the free-energy landscape of P450cam channels toward favoring the diffusion of water molecules out of the protein active site.

Copyright © 2011 Biophysical Society. Published by Elsevier Inc. All rights reserved.

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