Septins and flaviviral proteases: a structural analysis

Abstract

In 2016, during the Zika outbreak in Brazil, an increase of 26 times in microcephaly cases was reported, shocking the country. In these cases, during infection, the virus mainly targets neuronal progenitor cells (NPCs), decreasing their proliferation that leads to cell death, which contributes to microcephaly. By identifying the isolated effect of viral proteins on these cells, Li et al. (2019) observed that NS2B-NS3 protease is able to mediate virus neurotoxicity by promoting the cleavage of host proteins essential to neurogenesis (especially septins). After protease overexpression, they observed a reduction in the levels of these proteins, which reinforced them as a target. Septins are GTP-binding proteins that interact with each other forming heterocomplexes, filaments, and high order structures through the G (nucleotide-binding) domain and the N- and C-terminal domains. In the same study, the cytotoxic effects were related to the cleavage of the septin 2 C-terminal domain. After expression of cleavage-resistant septins, it was possible to rescue cytokinesis. Although cellular effects (after cleavage) have been determined, the immediate effect and importance of the cleaved region on the formation of septin structures are unknown. It is also unclear whether septin cleavage is a Zika-specific event or whether other flavivirus proteases can cleave them. Thus, this project will use truncated septin constructs (mimicking the protease effect) for the assembly of heterocomplexes in order to characterize them and evaluate polymerization abilities. We also want to perform an analysis of the interaction and the proteolytic activity assays involving septins and different flavivirus proteases will also be performed. Finally, crystallization assays will be performed with septin complexes and with complexes between septins and inactive versions of these proteases. We hope these results will help to understand the implications of septin 2 cleavage and its relationship to microcephaly. (AU)