Structural aspects of tubulins and microtubules (MTs). (A) MTs grow through head-to-tail polymerization of α-/ß-tubulin heterodimers into protofilaments that arrange into hollow tubes through lateral interactions. The α-and ß-tubulin monomers need to be folded properly assisted by chaperones, they heterodimerize through longitudinal interactions (peach arrow), they bind GTP (of which GTP on ß-tubulin tends to undergo hydrolysis to GDP) and undergo a number of posttranslational modifications, including de-tyrosination (often followed by de-glutamylation resulting in ∆2-tubulin), acetylation, poly-amination, (poly-)glycylation and (poly-)glutamylation . MTBPs primarily interact with the C-terminus of tubulins which sticks out from the MT surface. (B) The secondary structure of α- and ß-tubulin (color-coded as in A) showing the positions of ß-sheets (B1-10) and α-helices (H1-12; image modified from ); the borders and principal functions of the N-terminal, intermediate and C-terminal domains of ß-tubulin are indicated at the bottom and arrows indicate examples of posttranslational modification sites [11, 21]. Positions of known dominant-negative mutations are shown below the two secondary structures . Those mutations tested by Niwa and colleagues are highlighted in light blue, asterisks indicate those mutations that impair tubulin incorporation into MTs and blue arrowheads indicate the two charge-changing mutations in H12 .