Fig. 5: M-loop gets ordered upon forming one side of the lateral contacts of “MT-bond”.

a–d Structural comparison between the initial state of GMPCPP-tubulin heterodimer in solution (blue) and the intermediate state of tubulin heterodimer in the Tube lattice (orange). Models are superimposed on the α-tubulin. The direction of movement is marked by the blue arrow. a Side view. The inset shows the movements of M-loop and its surrounding regions (same for c). b Displacement vectors of β-tubulin Cα coordinates comparison between two tubulin heterodimers shown in (a). The length of the stick correlates with its displacement (same for d). c, d Structural changes (c) and β-tubulin displacement vectors (d) shown from the tangential direction. e Structural changes of β-tubulin upon forming the one side of “MT-bond” with neighboring tubulin heterodimer. Two neighboring tubulin heterodimer models forming “MT-bond” in the Tube lattice are colored with medium purple and orange. The GMPCPP-tubulin heterodimer model in solution is colored in cornflower blue. The structure model of GMPCPP-tubulin heterodimer in solution is superimposed on the tubulin heterodimer (orange) in the Tube lattice, using α-tubulin as reference. The inset is a zoom-in view of key components of lateral contacts, including M-loop.