title: Entrapment of water by subunit c of ATP synthase.
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.
authors.affiliation: Department of Molecular and Cellular Biology, Harvard University, 7 Divinity Avenue, Cambridge, MA 02138, USA. mcgeoch@fas.harvard.edu
authors.forename: Julie E M
authors.initials: JE
authors.lastname: McGeoch
authors.forename: Malcolm W
authors.initials: MW
authors.lastname: McGeoch
mesh_terms: D025181:ATP Synthetase Complexes / Q000737:chemistry* / Q000648:ultrastructure*; D003461:Crystallography; D006860:Hydrogen Bonding; D008854:Microscopy, Electron; D011487:Protein Conformation; D021122:Protein Subunits / Q000737:chemistry*; D013696:Temperature; D014867:Water / Q000737:chemistry*
chemical_list: D021122:Protein Subunits; D014867:Water; D025181:ATP Synthetase Complexes