Understanding Mechanisms of Nuclear Transport During Viral Infection

Many proteins migrate to the nucleus by binding with specialist receptors, known as importins (IMPs). To date, the overall steps and components involved in nuclear import pathways are well defined, however, the point of cargo recognition by IMPs, the nuclear localization signal (NLS), varies between cargoes. Furthermore, cellular proteins not only make use of this pathway, since numerous viruses hijack import receptors using NLS mimics. Nucleocytoplasmic shuttling is often critical for viral replication, proliferation, pathogenesis, and evasion of the host immune response. This doctoral study has investigated the molecular details of interactions between NLSs with IMP proteins, using structural biology techniques. Here, the IMP binding of NLSs from the human T cell lymphotropic virus type 1 (HTLV-1) basic leucine zipper factor (HBZ), polyomavirus (PyV) large T antigens (LTAs), human cytomegalovirus (HCMV) DNA polymerase processivity factor (UL44), and human parvovirus B19 (B19V) non-structural protein 1 (NS1), have been studied. The NLSs of key innate immune proteins involved in the host antiviral response, known as interferon regulatory factors (IRFs), were also examined. In addition, a novel homodimer of the IMPα1 transport receptor was structurally characterized and its redox sensitivity tested. This research has incorporated numerous techniques to investigate the molecular binding determinants of these protein-protein interactions, including use of X-ray crystallography and small angle X-ray scattering. Understanding the IMP binding interfaces of viral NLSs is important since these interactions are attractive targets for the development of novel antiviral inhibitors. Further to this, understanding the import of IRF proteins and the overall behaviour of IMP receptors, like dimerization, enhances our understanding of nuclear trafficking and cell biology.