The association of the surface array and the outer membrane of Deinococcus radiodurans

Publisher Website
Google Scholar
Abstract
The hexagonal surface array of D. radiodurans strain Sark exhibits remarkably strong bonding of its subunits and association with the outer membrane. The array is not dissociated nor is it separated from the outer membrane by reagents that disrupt H bonds (urea, guanidine hydrochloride), ionic bonds (pH, LiCl, KCl, NaCl), disulfide bonds (.beta.-mercaptoethanol, dithiothreitol), or chelating agents (EDTA). Only disruption of the outer membrane with sodium dodecyl sulfate at room temperature separated the 2 layers. The isolated array was composed of a major protein of 115,000 MW, a minor protein of 108,000 MW and no other polymers. Their amino acid profile was indicative of a protein, lacking proline, with a high proportion (51.2%, mol/mol) of polar amino acids. The electron-transparent layer between the hexagonal surface array and the outer membrane was still associated with the purified array, suggesting that the electron-transparent layer is a component of the protein array and impenetrable to stains so that the reactive groups are inaccessible. The observations suggest that hydrophobic amino acids make up a major domain of the array molecule and that nonspecific hydrophobic interactions are a large component of the forces involved in the tight association of the array within itself and with the underlying outer membrane. The surface of a mutant lacking the hexagonal surface array was compared with the surface of the wild type that possesses the hexagonal surface array using the 2 phase droplet system of Schuerch et al. to estimate the relative surface hydration. The contact angle for the mutant lacking the array was 128.8 .+-. 0.8, n = 39 and the contact angle for the wild type was 92.6 .+-. 1.4, n = 39, indicating that the surface of the outer membrane is relatively more hydrophobic than the outer aspect of the hexagonal surface array.