Isotype expression, post-translational modification and stage-dependent production of tubulins in erythrocytic Plasmodium falciparum.

Microtubules are cytoskeletal polymers containing repeating alpha/beta-tubulin heterodimers and are found in all eukaryotes including the malaria parasite Plasmodium falciparum. Diverse cellular functions such as chromosomal segregation, organelle transport and the determination of cell shape and motility are all dependent on microtubules. This essential role played by tubulin in cells is reflected in the effective use of anti-microtubule agents as fungicides, herbicides, anti-parasitic and anti-cancer agents. Plasmodium falciparum microtubules have been proposed as a potential antimalarial drug target and knowledge of their molecular composition and cellular architecture in blood-stage parasites is required to substantiate this premise. We report here that: (i) the two alpha-tubulin isotypes, alphaI- and alphaII-tubulin, are produced in both asexual and sexual blood-stage parasites, contrary to the previous report that alphaII-tubulin was specific to male gametocytes; (ii) tubulin production is highly stage-dependent in asexual parasites, reaching its maximum level in schizonts and segmenters and (iii) there is evidence of post-translational polyglutamylation of tubulin. The glutamylation of P. falciparum tubulins is the first reported post-translational modification of tubulin in this organism and was found only in the microtubule-organising centres and post-mitotic microtubular structures, suggesting possible roles for this modification in spindle pole body formation and merozoite biogenesis. Taken together, these findings form the basis for a better biological appreciation of P. falciparum microtubules and for the correct deployment of purified tubulins in the evaluation of microtubule inhibitors as potential antimalarial drugs.