1.A.63.1.1
The α-helical pore-forming outer membrane nanomeric porin, Imp1227 or Ihomp1, of 85 aas and one TMS. The membrane protein Imp1227 is the main protein constituent of the unique outer sheath of the hyperthermophilic, chemolithoautotrophic archaeum Ignicoccus hospitalis. With its molecular mass of only 6.23 kDa, Imp1227 is found to be incorporated into the outer membrane to form large, stable complexes. When separated by SDS-PAGE, they exhibit apparent masses of about 150, 50, 45 and 35 kDa.  Electron micrographs of negatively stained samples confirmed that isolated membranes are tightly packed with round complexes, about 7 nm in diameter, with a central, stain-filled 2 nm pore; a local two-dimensional crystalline arrangement in the form of small patches can be seen by tomographic reconstruction. Using secondary structure predictions and molecular modelling, an alpha-helical transmembrane domain is proposed; for the oligomer, a ring-shaped nonamer with a central 2 nm pore was a likely arrangement.