Fig. 6.

Molecular model of LFA-1 orientation on the cell surface. a Schematic of the integrin-microscope reference frame. b, c Details of the integrin-microscope reference frame. xy and xz planes are black and blue grids, respectively. Integrin Cα atoms used to define the origin (red), x axis (gold), and xz plane (silver) are shown as large spheres. The GFP transition dipole (red) and its projection on the image plane (yellow–orange) are shown as cylinders with cones at each end. A spherical coordinate radial marker r (red arrow) is used to compare integrin orientations between the reference state with θ = 0° and ϕ = 90° b and integrin orientation with θ = 0° and ϕ = 45° that fits data well c. Inset shows relation between Cartesian coordinates and spherical coordinates with ϕ measured between the z axis and radial marker (r) and θ measured between the projection of r in the xy plane and the x axis. d, e The image plane with dipole positions of Rosetta ensemble members (lowest 40% in energy) projected from a spherical surface and shown as open gray circles for αL-T d and αL-F e. Projections are shown in the reference frame with θ = 0° and tilts in ϕ ranging from 11.25 to 67.5°. Silver, red, and gold circles show the same integrin reference atoms as in b & c. The calculated ensemble transition dipole⁵⁷ is projected as a green line with length proportional to p. The transition dipole orientation determined by FluoPolScope is shown as black line with ± 1 s.d. shown as dashed lines. f Schematic showing integrin and GFP dipole orientation relative to tensile force between the actin cytoskeleton and ICAM (arrows) in migrating cells. g Model of cytoskeletal force acting on an integrin drawn to scale tilted at ϕ = 45°. Structures^{15,20–22,56,58–60} were assembled and rotated at domain–domain junctions known to be flexible and depicted with PyMol