Structure of p15 trypanosome microtubule associated protein.

Trypanosomes are protozoan parasites, containing subpellicular microtubules that are crosslinked to one another and to the plasma membrane by unique microtubule associate proteins (MAPs). One of these MAPs, purified from the subpellicular microtubules by a tubulin affinity column, is termed p15alpha. This protein was shown to be specific to the subpellicular microtubules by immunoelectron microscopy and was also shown to induce microtubule bundling. We show here that the gene coding for p15alpha is present in multiple copies. It is 258 bp long and contains 16 highly organized 15 bp long repetitive sequences. The deduced amino acid sequence indicates that p15alpha contains 16 highly organized, nearly identical tandem repeats, with a periodicity of five amino acids, which are rich in positively charged and in non-polar (hydrophobic) amino acids. The p15 family is unique to trypanosomes and has no significant sequence homology to other species. p15 can bind both tubulin and phospholipids in vitro and is therefore hypothesized to contribute to the stability of the trypanosome subpellicular microtubules.