New NLSs and NESs. With the exception of Impβ, Kapβ2, Imp5 (Kap121 in S. cerevisiae),TrnSR/TrnSR2/TNPO3 and CRM1, the other 15 Kaps are currently known to each recognize only a few diverse sequences, making it extremely difficult to identify their NLSs/NESs. Nevertheless, large sizes, low sequence identities of the Kaps and identification of multiple cargo binding sites for several members all suggest that dozens of NLSs and NESs have yet to be discovered. Our Kapβ2 and CRM1 work now serve as model systems for future discovery of NLSs and NESs. We have discovered and are studying complex signals using a collection of physical rules rather than specific sequence motifs alone. This concept could be expanded to study numerous obscure targeting signals in eukaryotic cells and other biological recognition processes that involve linear recognition motifs with weak and obscure consensus sequences.

Design of pathway specific nuclear transport inhibitors. A deep understanding of structure and thermodynamics of PY-NLS recognition led us to design the M9M inhibitor which specifically inhibits the Kapβ2 (or Transportin) pathway. We will apply similar structure-based approaches to generate specific inhibitors for individual Kap pathways.

Nuclear targeting signals and their inhibitors in human diseases. Nuclear-cytoplasmic trafficking is a fundamental process in eukaryotic cells. It is therefore tremendously exciting that our basic science studies have also directly contributed to the understanding of mechanisms of a neurodegenerative disease and to the development of anti-cancer drugs. We will investigate the roles of NLSs and Importins in neurodegenerative diseases. We will also develop methods to accurately identify new NESs and CRM1 cargos, as well as study chemical and cellular mechanisms of CRM1 inhibitors that target cancer, inflammatory and viral diseases.