A family of aspartic proteases and a novel, dynamic and cell-cycle-dependent protease localization in the secretory pathway of Toxoplasma gondii

Aspartic proteases are important virulence factors in pathogens like HIV, Candida albicans or Plasmodium falciparum. We report here the identification of seven putative aspartic proteases, TgASP1 to TgASP7, in the apicomplexan parasite Toxoplasma gondii. Bioinformatic and phylogenetic analysis of the TgASPs and other aspartic proteases from related Apicomplexa suggests the existence of five distinct groups of aspartic proteases with different evolutionary lineages. The members of each group share predicted biological features that validate the phylogeny. TgASP1 is expressed in tachyzoites, the rapidly dividing asexual stage of T. gondii. We present the proteolytic maturation and subcellular localization of this protease through the cell cycle. TgASP1 shows a novel punctate localization associated with the secretory system in non-dividing cells, and relocalizes dramatically and unambiguously to the nascent inner membrane complex of daughter cells at replication, before coalescing again at the end of division.