Toxoplasma gondii toxolysin 4 is an extensively processed putative metalloproteinase secreted from micronemes

Proteases play central roles in cell invasion by Toxoplasma gondii and other apicomplexan parasites. Herein we report the cloning and characterization of a novel secretory putative metalloproteinase, Toxolysin 4 (TLN4). T. gondii tachyzoites store TLN4 in the micronemes and secrete it in response to elevated calcium, suggesting a possible role in cell invasion. TLN4 is initially synthesized as a large (∼260 kDa) precursor, which is extensively processed into multiple proteolytic fragments within the parasite secretory system. At least some of these proteolytic fragments remain associated in a large molecular complex. Whereas precomplementation with the TLN4 cDNA allowed disruption of the TLN4 gene, multiple attempts to directly knockout TLN4 without precomplementation failed. TLN4 knockout parasites were detected by PCR in transfected populations but were lost from the cultures during drug selection and growth suggesting that TLN4 contributes to parasite fitness.

Toxoplasma gondii toxolysin 4 is an extensively processed microneme secretory metalloproteinase.203Research highlights► Toxoplasma TLN4 is a large putative metalloproteinase. ► TLN4 is proteolytically processed into multiple fragments that remain together in a protein complex. ► TLN4 is stored in the micronemes and secreted in a calcium stimulated manner. ► Multiple attempts to disrupt TLN4 were unsuccessful suggesting that TLN4 contributes to parasite fitness.