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Functional importance of Glutamate-445 and Glutamate-99 in proton-coupled electron transfer during oxygen reduction by cytochrome bd from Escherichia coli

Murali, Ranjani and Gennis, Robert B. (2018) Functional importance of Glutamate-445 and Glutamate-99 in proton-coupled electron transfer during oxygen reduction by cytochrome bd from Escherichia coli. Biochimica et Biophysica Acta - Bioenergetics, 1859 (8). pp. 577-590. ISSN 0005-2728 . PMCID PMC5994205. http://resolver.caltech.edu/CaltechAUTHORS:20180711-161227242

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Abstract

The recent X-ray structure of the cytochrome bd respiratory oxygen reductase showed that two of the three heme components, heme d and heme b, have glutamic acid as an axial ligand. No other native heme proteins are known to have glutamic acid axial ligands. In this work, site-directed mutagenesis is used to probe the roles of these glutamic acids, E445 and E99 in the E. coli enzyme. It is concluded that neither glutamate is a strong ligand to the heme Fe and they are not the major determinates of heme binding to the protein. Although very important, neither glutamate is absolutely essential for catalytic function. The close interactions between the three hemes in cyt bd result in highly cooperative properties. For example, mutation of E445, which is near heme d, has its greatest effects on the properties of heme b and heme b. It is concluded that 1) O binds to the hydrophilic side of heme d and displaces E445; 2) E445 forms a salt bridge with R448 within the O binding pocket, and both residues play a role to stabilize oxygenated states of heme d during catalysis; 3) E445 and E99 are each protonated accompanying electron transfer to heme d and heme b, respectively; 4) All protons used to generate water within the heme d active site come from the cytoplasm and are delivered through a channel that must include internal water molecules to assist proton transfer: [cytoplasm] → E107 → E99 (heme b) → E445 (heme d) → oxygenated heme d.


Item Type:Article
Related URLs:
URLURL TypeDescription
https://doi.org/10.1016/j.bbabio.2018.04.012DOIArticle
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5994205/PubMed CentralArticle
Additional Information:© 2018 Elsevier. Received 12 February 2018, Revised 25 April 2018, Accepted 26 April 2018, Available online 30 April 2018.
Subject Keywords:Cytochrome bd; Respiration; Heme; Proton transfer
PubMed Central ID:PMC5994205
Record Number:CaltechAUTHORS:20180711-161227242
Persistent URL:http://resolver.caltech.edu/CaltechAUTHORS:20180711-161227242
Official Citation:Ranjani Murali, Robert B. Gennis, Functional importance of Glutamate-445 and Glutamate-99 in proton-coupled electron transfer during oxygen reduction by cytochrome bd from Escherichia coli, Biochimica et Biophysica Acta (BBA) - Bioenergetics, Volume 1859, Issue 8, 2018, Pages 577-590, ISSN 0005-2728, https://doi.org/10.1016/j.bbabio.2018.04.012. (http://www.sciencedirect.com/science/article/pii/S0005272818300884)
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:87782
Collection:CaltechAUTHORS
Deposited By: George Porter
Deposited On:12 Jul 2018 13:52
Last Modified:12 Jul 2018 13:52

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