Nuclear Import

Nuclear import is an essential pathway in eukaryotes and the lab studies this pathway in apicomplexan parasites as a potential therapeutic target. Over the last several years, we have characterised importin alpha proteins from Plasmodium falciparum and Toxoplasma gondii and established that they possess significant differences from their human orthologs. While mammalian importin α proteins show a regulatory mechanism termed auto-inhibition, we found P. falciparum importin α exhibits a lack of auto-inhibition, and T. gondii importin α exhibits weak auto-inhibition. This indicates that the parasite nuclear transport machinery may be uniquely susceptible to selective inhibition.

In a high-throughput screening assay, we identified and characterized small-molecule inhibitors that selectively disrupt nuclear transport in different developmental stages in T. gondii and P. falciparum by targeting importin α. In our recent studies, we show that the expression of the classical SV40 T-antigen nuclear localisation signal (NLS) results in loss of parasite viability, which can be rescued by over-expression of importin α. These results give direct evidence that disruption of the nuclear import machinery can be lethal to T. gondii. Importantly, the SV40 T-ag NLS shows no toxicity to human cells. The molecular details of the interactions between T. gondii importin α and the SV40 T-ag NLS are being studied using in silico modelling and Molecular Dynamics simulations.

Toxoplasma gondii importin α with SV40 T-ag NLS peptide bound in the major NLS binding site (Image credit: Diksha Mehta)