The tubulin superfamily includes five distinct families, the alpha-, beta-, gamma-, delta-, and epsilon-tubulins and a sixth family (zeta-tubulin) which is present only in kinetoplastid protozoa. The alpha- and beta-tubulins are the major components of microtubules, while gamma-tubulin plays a major role in the nucleation of microtubule assembly. The delta- and epsilon-tubulins are widespread but unlike the alpha, beta, and gamma-tubulins they are not ubiquitous among eukaryotes. Delta-tubulin plays an essential role in forming the triplet microtubules of centrioles and basal bodies.
Jiyao W et al.(2023). "The conserved domain database in 2023.",