Structural basis for importin Alpha 3 binding specificity of W proteins in Hendra and Nipah viruses

Forwood JK1, Smith K1, Tsimbulyak S1, Cross E1, Soares Dacosta T2, Aragao D3, Edwards M4 and Basler C4

  1. Charles Sturt University.
  2. La Trobe University.
  3. Australian Synchrotron.
  4. Georgia State University.

Nucleocytoplasmic transport of proteins is an essential cellular process that mediates gene expression, cell differentiation, and a wide range of disease pathways, including cancer and virus infection. Nuclear translocation of proteins via the classical import pathway is initiated upon recognition of a nuclear localization signal (NLS) by a member of the importin α subfamily. There are seven human isoforms of importin α that mediate nuclear import of cargo in a tissue- and isoform-specific manner. Our understanding as to how nuclear import adaptors differentially interact with cargo harbouring the same NLS remains poorly understood as all importin α isoforms are conserved in the domain responsible for NLS recognition. Here, we provide a structural basis for the nuclear import specificity of the W proteins of Hendra virus (HeV) and Nipah virus (NiV). Using structural approaches, we identify the interaction interfaces between importin α1 and α3 for the W proteins of both HeV and NiV, highlighting marked differences including a 2.4-fold more extensive interface and >50-fold binding affinity for importin α3. Using structure-guided design of importin α1 and α3 chimeric and mutant proteins, together with structures of importin α1 and α3 isoforms without cargo in the binding site, we establish that the molecular basis of specificity resides in the differential positioning of the armadillo (ARM)-repeats 7 and 8. Overall, our study provides new mechanistic insights into a range of important cellular and disease processes that are reliant on isoform specificity of nuclear import adaptors.