Flexibility analysis. (a) A representative view of the new ensemble map and the two new classes showing the `open conformation' in Class 1 and the `closed conformation' in Class 2. Note the elastic analysis of deformations performed on the Class 1 and Class 2 maps (see the main text), with 1s referring to `stretching' and 1r to `rotations'. The color code is from blue for minimal deformation to red for maximal deformation. The scale bar is 5 nm in length. (b) Representation of the angles defined by the spike when transitioning between the opened and closed states. The regions shown in magenta represent the hinges used by the RBD domain to pivot. Note that each hinge encompasses two different chain regions. The first hinge spans amino acids 318–326 and 588–595, while the second hinge is defined by amino acids 330–335 and 527–531. The angles were measured using PyMOL.