Regulation of motor proteins by tubulin carboxy-terminal tails.

Microtubules (MTs), cytoskeletal polymers of a/b-tubulin heterodimers, interact with many MT-associated proteins (MAPs) to carry out various cellular functions. Multiple a- and b-tubulin isotype­sare present in higher eukaryotes, while their structural core is highly conserved, most of the amino acid variation is confined to the unstructured C-terminal tails (CTTs).In addition the CTTs of tubulins undergo several posttranslational modifications (PTMs). The presence of numerous tubulin gene products and PTMs resulted in the ‘tubuliln-code’ hypothesis, which proposes that distinct tubulin isotypes or PTMs offer unique interactions with MAPs for specific cellular function.So far lack of systems to obtain homogenous tubulin isotypes has hindered biochemical testing of this hypothesis. Here we focused on engineering tubulin with distinctCTTs and PTMs. Using yeast expression system a comprehensive series of (>30) unique CTT engineered recombinant tubulins were purified and tested their interaction against four distinct motor proteins. Single molecule assays of these motor proteins revealed that each motor recognizes unique molecular signatures present in the CTTs for their optimal function. In addition we demonstrate motor preference towards different tubulin isotypes and their cross-regulation by PTMs. Identifying how different motor proteins perceive unique CTT molecular signatures strengthens the notion of tubulin-code hypothesis.