Figure 4. Trans-acting model of growth and lattice cooperativity.

(A) Cis-acting model proposes that the nucleotide state of the incoming tubulin dictates binding affinity. Trans-acting model proposes that the nucleotide state of the terminal lattice-bound tubulin dictates binding affinity.

(B) Effect of a single tubulin’s compaction not only has the potential to change the bond strength of nearest neighbors but can be spread through accommodation within the lattice.

(C) Cooperative trans-acting model proposes that the nucleotide states of neighboring tubulin in the lattice dictate the binding affinity of the incoming tubulin⁴⁴.

(D) Structural features that may limit the propagation of cooperative binding effects through the lattice. Local curvature changes in ‘crinkled’ or ‘squished’ microtubule lattices (left) and multiple seams (right) may limit the size of the neighborhood over which cooperative effects may act. Images of deformed microtubules based on Debs et al. (2020)⁹⁴