What is it about?
The high resolution structure of the membrane enzyme cytochrome bo3 was determined using cryo-electron microscopy. The structure includes internal water molecules that are critical to function, phospholipids bound to the enzyme surface and one molecule of ubiquinone-8, the oxidized form of the natural substrate.
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Why is it important?
The structure reveals the evolutionary modifications that allow this enzyme to use the hydrophobic substrate, ubiquinol-8 in place of cytochrome c, the substrate of closely related enzymes. The binding site is a non-linear, winding groove along the membrane-facing surface of the protein. The structural data indicates a highly dynamic protein at the binding site, presumably facilitating rapid binding an release of the substrate/product. The structure was determined in two different types of nanodiscs: one formed with SMALPS (styrene-maleic acid copolymer) without detergent and the second formed with membrane scaffold protein. The protein structures were very similar in the two different preparations.
Perspectives
For many years it was thought that the enzyme has two binding sites for ubiquinol-8. Recent biochemical studies from our laboratory (RBG) suggested only one binding site. Spectroscopic data from our laboratory also indicated a set of residues hydrogen bonded to the substrate at this site. The structure verified the one-binding-site conclusion and validated the model of how the ubiquinol-8 is hydrogen bonded to the protein. The value of SMALPS to replace traditional detergents and retain the native structure was also validated in these studies. This is the second structure of a membrane protein in which we have used SMA copolymer to avoid the use of traditional detergents.
Robert Gennis
University of Illinois at Urbana-Champaign
Read the Original
This page is a summary of: Cryo-EM structures of
Escherichia coli
cytochrome
bo
3
reveal bound phospholipids and ubiquinone-8 in a dynamic substrate binding site, Proceedings of the National Academy of Sciences, August 2021, Proceedings of the National Academy of Sciences,
DOI: 10.1073/pnas.2106750118.
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