Figure 2: Architecture of GtrB, an integral membrane PI-GT.

The tetrameric assembly of GtrB, in which each of the four polypeptide chains is represented as a ribbon drawn in a different colour, is shown here (a) from a position orthogonal to the TM helices and (b) looking down the fourfold symmetry axis of the tetramer from the extracellular side. (c) A single protomer is shown. The protomer is comprised of a GT-A fold GT domain (orange), two amphipathic juxtamembrane helices (grey; juxtamembrane (JM)), two TM helices (blue) and a C-terminal β-hairpin (red). (d,e) The GtrB tetramer is shown in the same two views and orientations as in a,b, with three subunits represented in grey ribbons and the fourth in rainbow colouring from the N-terminus (blue) to the C-terminus (red). (f) The GtrB monomer shown in the same orientation as in c, represented in rainbow colouring from the N-terminus (N; blue) to the C-terminus (C; red).