Nuclear Import

The first step towards a new antimalarial drug discovery is to find an essential protein that can be blocked by a drug, thus preventing the disease. One such protein is importin alpha of Plasmodium falciparum (Pf importin alpha). Importin alpha is a key component in nucleocytoplasmic transport. It is an adaptor protein that recognizes the nuclear localization signal (NLS) and directs these proteins into the nucleus. The regulation of this pathway is largely conferred by importin alpha through its property of autoinhibition by its Importin beta binding (IBB) domain. We showed that P. falciparum importin alpha lacks this autoinhibitory function, while Toxoplasma gondii importin alpha exhibits weak autoinhibition. These observations are surprising because autoinhibition is found in all importin alpha proteins studied so far, and a protein lacking autoinhibition does not support cell viability in Saccharomyces cerevisiae. 

We developed an in vitro system exploiting this unconventional facet of P. falciparum importin alpha to screen inhibitors of nucleocytoplasmic transport. We found several small molecules that inhibit importin alpha binding to NLSs, for both P. falciparum and Toxoplasma gondii. These molecules also block nuclear transport and compromise cell viability in both parasites. Interestingly, some of the small molecules affect the viability of differentiated stages as well. Recent work involves development of peptide inhibitors that have higher specificity for parasite nuclear import compared to the human host.

We are also studying the biological implications of the lack of auto-inhibition of parasite importin alpha in Toxoplasma gondii and doing structural biology to understand unique features of these proteins. 

Funded by: Department of Biotechnology (BT/PR4239/BRB/10/1005/2011), Department of Science & Technology - Science & Engineering Research Board (CRG/2018/000129), International Centre for Genetic Engineering and Biotechnology (ICGEB) for funding (Grant No. CRP/22/005).