A nematode microtubule-associated protein, PTL-1, closely resembles its mammalian counterparts in overall molecular architecture*

Abstract

Abstract The mammalian microtubule-associated proteins (MAPs), MAP2, MAP4, and τ, are structurally similar and considered to be evolutionarily related. The primary structure of a nematode MAP, PTL-1, also reportedly resembles those of the MAPs, but only in a small portion of the molecule. In this study, we elucidated the overall domain organization of PTL-1, using a molecular dissection technique. Firstly, we isolated nematode microtubules and proved that the recombinant PTL-1 binds to nematode and porcine microtubules with similar affinities. Then, the recombinant PTL-1 was genetically dissected to generate four shorter polypeptides, and their microtubule-binding and assembly promoting activities were assessed, using porcine microtubules and tubulin. PTL-1 was found to consist of two parts, microtubule-binding and projection domains, with the former further divided into three functionally distinct subdomains. The molecular architecture of PTL-1 was proved to be quite analogous to its mammalian counterparts, MAP2, MAP4, and τ, strongly supporting their evolutionary relationships.