Structural intermediates in the low pH-induced transition of influenza hemagglutinin
Fig 3
Structure comparisons of the pH 7.8 and pH 5.2 conformations.
(A) Structure superimpositions of the central helices in neutral (cornflower blue) and low pH conformations (hot pink). Side view (left) and bottom-up view (right) are shown. The coiled-coil parameters of the Helix Cs and the Helix Ds in neutral and low pH conformations are listed under the top view. The rotation directions of the membrane-proximal ends are indicated by black arrows in the bottom-up view. The rotation angles of the helices are measured with the membrane-distal ends as the pivot point. (B) Structure comparisons between the Helix Ds in neutral (cornflower blue) and low pH (hot pink) conformations showing the changes in the residue side chains. (C) Ribbon and surface-rendered diagrams showing the surface electrostatic potential changes of the central helices upon pH change. The surface is colored according to the surface electrostatic potential with positive charges colored blue and negative charges colored red. (D) Surface-rendered diagrams showing the changes in surface and inner cavity of the central helices upon pH change. The surface is colored from white to green to purple according to the distances from the voxels to the three-fold axis.