A conserved subtilisin-like protein TgSUB1 in microneme organelles of Toxoplasma gondii

Proteolytic processing plays a significant role in the process of invasion by the obligate intracellular parasite Toxoplasma gondii. We have cloned a gene, TgSUB1, encoding for a subtilisin-type serine protease found in T. go ndii tachyzoites. TgSUB1 protein is homologous to other Apicomplexan and ba cterial subtilisins and is processed within the secretory pathway of the pa rasite. Initial cleavage occurs in the endoplasmic reticulum, after which t he protein is transported to micronemes, vesicles that secrete early during host cell invasion. Upon stimulation of microneme secretion, TgSUB1 is cle aved into smaller products that are secreted from the parasite. This second ary processing is inhibited by brefeldin A and serine protease inhibitors. TgSUB1 is a candidate processing enzyme for several microneme proteins clea ved within the secretory pathway or during invasion.