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Entrapment of water by subunit c of ATP synthase.

McGeoch JE, McGeoch MW - J R Soc Interface (2008)

Bottom Line: Protein sheets with an intra-sheet backbone spacing of 3.7A and inter-sheet spacing of 6.0 A hydrogen bond into long ribbons or continuous surfaces to completely encapsulate a water droplet.Electron diffraction shows the crystals to be highly ordered and compressed and the protein skin to resemble beta-sheets.The protein skin can retain the entrapped water over a temperature rise from 123 to 223 K at 1 x 10(-4) Pa, whereas free water starts to sublime significantly at 153 K.

View Article: PubMed Central - PubMed

Affiliation: Department of Molecular and Cellular Biology, Harvard University, 7 Divinity Avenue, Cambridge, MA 02138, USA. mcgeoch@fas.harvard.edu

ABSTRACT
We consider an ancient protein, and water as a smooth surface, and show that the interaction of the two allows the protein to change its hydrogen bonding to encapsulate the water. This property could have made a three-dimensional microenvironment, 3-4 Gyr ago, for the evolution of subsequent complex water-based chemistry. Proteolipid, subunit c of ATP synthase, when presented with a water surface, changes its hydrogen bonding from an alpha-helix to beta-sheet-like configuration and moves away from its previous association with lipid to interact with water surface molecules. Protein sheets with an intra-sheet backbone spacing of 3.7A and inter-sheet spacing of 6.0 A hydrogen bond into long ribbons or continuous surfaces to completely encapsulate a water droplet. The resulting morphology is a spherical vesicle or a hexagonal crystal of water ice, encased by a skin of subunit c. Electron diffraction shows the crystals to be highly ordered and compressed and the protein skin to resemble beta-sheets. The protein skin can retain the entrapped water over a temperature rise from 123 to 223 K at 1 x 10(-4) Pa, whereas free water starts to sublime significantly at 153 K.

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TEM images of transitional forms of subunit c encapsulating water. (a) Spacious vesicles with central crystals. (b) Vesicles whose sides are beginning to straighten. (c) Spherical vesicles with attached hexagon crystals. (d) Transitional vesicles and crystals attached to one another. Scale bars, 100 nm.
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fig4: TEM images of transitional forms of subunit c encapsulating water. (a) Spacious vesicles with central crystals. (b) Vesicles whose sides are beginning to straighten. (c) Spherical vesicles with attached hexagon crystals. (d) Transitional vesicles and crystals attached to one another. Scale bars, 100 nm.

Mentions: The TEM images reveal that the water morphology is a sphere or a hexagonal crystal that is encapsulated by a skin of subunit c. Spacious vesicles around hexagonal ice crystals (figure 4a), vesicles whose sides are beginning to flatten as they abut part of a crystal edge (figure 4b), vesicles joined to crystals (figure 4c) and vesicles and crystals attached to one another where each morphology is in transition (figure 4d) are present. Basically, the skin of subunit c winds around the water (figure 5a). It is necessary at this point to define the terms used to describe the TEM imaged subunit c morphologies. The smallest unit of subunit c is termed a ‘strand’ and is the carbon backbone of the protein, which is electron dense due to its planar-amide bonds. ‘Sheets’ are composed of 17–24 laterally spaced strands with a lateral spacing of 3.7 Å (figure 5b), connected inter-molecularly by β-sheet-type hydrogen bonds. A ‘ribbon’ is a very long sheet that can consist of one or several sheet layers and extend continuously for hundreds of nanometres. The edges of the ribbons that face away from the vesicle body have an area of α-helices, and therefore have both β-sheet and α-helix hydrogen bonding in the subunit c protein. The ribbon of subunit c that runs diagonally across in figure 5b is from the right-side edge of the vesicle in figure 5a, in which the outer sheet structure is more loosely wound, allowing clear imaging. It has 24 strands laterally, and lengthways the alignment goes across the image for greater than 134 nm. Going further left into the vesicle, criss-crossing ribbons can be seen. Images of the ribbons cladding the vertical edges of crystals of water, perpendicular to the flat ribbon direction above, show that the spacing is 6 Å between the sheet planes (figure 6d). The same image shows that the ribbons of subunit c around the crystal bend to accommodate the 60° angle turn.


Entrapment of water by subunit c of ATP synthase.

McGeoch JE, McGeoch MW - J R Soc Interface (2008)

TEM images of transitional forms of subunit c encapsulating water. (a) Spacious vesicles with central crystals. (b) Vesicles whose sides are beginning to straighten. (c) Spherical vesicles with attached hexagon crystals. (d) Transitional vesicles and crystals attached to one another. Scale bars, 100 nm.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC2500151&req=5

fig4: TEM images of transitional forms of subunit c encapsulating water. (a) Spacious vesicles with central crystals. (b) Vesicles whose sides are beginning to straighten. (c) Spherical vesicles with attached hexagon crystals. (d) Transitional vesicles and crystals attached to one another. Scale bars, 100 nm.
Mentions: The TEM images reveal that the water morphology is a sphere or a hexagonal crystal that is encapsulated by a skin of subunit c. Spacious vesicles around hexagonal ice crystals (figure 4a), vesicles whose sides are beginning to flatten as they abut part of a crystal edge (figure 4b), vesicles joined to crystals (figure 4c) and vesicles and crystals attached to one another where each morphology is in transition (figure 4d) are present. Basically, the skin of subunit c winds around the water (figure 5a). It is necessary at this point to define the terms used to describe the TEM imaged subunit c morphologies. The smallest unit of subunit c is termed a ‘strand’ and is the carbon backbone of the protein, which is electron dense due to its planar-amide bonds. ‘Sheets’ are composed of 17–24 laterally spaced strands with a lateral spacing of 3.7 Å (figure 5b), connected inter-molecularly by β-sheet-type hydrogen bonds. A ‘ribbon’ is a very long sheet that can consist of one or several sheet layers and extend continuously for hundreds of nanometres. The edges of the ribbons that face away from the vesicle body have an area of α-helices, and therefore have both β-sheet and α-helix hydrogen bonding in the subunit c protein. The ribbon of subunit c that runs diagonally across in figure 5b is from the right-side edge of the vesicle in figure 5a, in which the outer sheet structure is more loosely wound, allowing clear imaging. It has 24 strands laterally, and lengthways the alignment goes across the image for greater than 134 nm. Going further left into the vesicle, criss-crossing ribbons can be seen. Images of the ribbons cladding the vertical edges of crystals of water, perpendicular to the flat ribbon direction above, show that the spacing is 6 Å between the sheet planes (figure 6d). The same image shows that the ribbons of subunit c around the crystal bend to accommodate the 60° angle turn.

Bottom Line: Protein sheets with an intra-sheet backbone spacing of 3.7A and inter-sheet spacing of 6.0 A hydrogen bond into long ribbons or continuous surfaces to completely encapsulate a water droplet.Electron diffraction shows the crystals to be highly ordered and compressed and the protein skin to resemble beta-sheets.The protein skin can retain the entrapped water over a temperature rise from 123 to 223 K at 1 x 10(-4) Pa, whereas free water starts to sublime significantly at 153 K.

View Article: PubMed Central - PubMed

Affiliation: Department of Molecular and Cellular Biology, Harvard University, 7 Divinity Avenue, Cambridge, MA 02138, USA. mcgeoch@fas.harvard.edu

ABSTRACT
We consider an ancient protein, and water as a smooth surface, and show that the interaction of the two allows the protein to change its hydrogen bonding to encapsulate the water. This property could have made a three-dimensional microenvironment, 3-4 Gyr ago, for the evolution of subsequent complex water-based chemistry. Proteolipid, subunit c of ATP synthase, when presented with a water surface, changes its hydrogen bonding from an alpha-helix to beta-sheet-like configuration and moves away from its previous association with lipid to interact with water surface molecules. Protein sheets with an intra-sheet backbone spacing of 3.7A and inter-sheet spacing of 6.0 A hydrogen bond into long ribbons or continuous surfaces to completely encapsulate a water droplet. The resulting morphology is a spherical vesicle or a hexagonal crystal of water ice, encased by a skin of subunit c. Electron diffraction shows the crystals to be highly ordered and compressed and the protein skin to resemble beta-sheets. The protein skin can retain the entrapped water over a temperature rise from 123 to 223 K at 1 x 10(-4) Pa, whereas free water starts to sublime significantly at 153 K.

Show MeSH
Related in: MedlinePlus