Molecular level evaluation of the dengue virus capsid protein role(s) on the virus life cycle

Tese de mestrado em Bioquímica, apresentada à Universidade de Lisboa, através da Faculdade de Ciências, 2011Viral hemorrhagic fever is mostly caused by dengue virus (DENV), which originates 100 million infections annually. DENV is a Flavivirus, member of the Flaviviridae family that also comprises other important human pathogens. This virus affects the host lipid metabolism, increasing intracellular lipid droplets (LDs) and imbalancing plasma lipoproteins levels and composition. Effective dengue treatments are not available yet, in part due to the poor understanding of some viral life cycle steps. The DENV capsid protein (DENV C) was recently found to interact with LDs, in a process that influences viral replication. However, the underlying molecular mechanisms of such interaction were not clear and also no function had already been attributed to its N-terminal disordered region. Moreover, human lipoproteins, similar to LDs in structure and composition, could play an important role in the dengue virus infectivity process. This study aimed at unraveling the molecular mechanism behind the DENV C protein interaction with host LDs and lipoproteins, which may explain key processes occurring in vivo. The understanding of the molecular nature and biological relevance of these interactions may also provide clues on how to inhibit them. In the present study, it was found that DENV C N-terminal region is crucial for the interaction with LDs and VLDL, requiring the presence of potassium. These interactions seem to occur mainly with LDs and VLDL intrinsic protein(s), rather than lipids. Importantly, pep14-23, a peptide based on the DENV C N-terminal conserved region, inhibits the C-LDs interaction. In contact with negative phospholipids, this peptide undergoes a structural conversion to α-helix. This lipid-driven structural conversion may thus help pep14-23 interaction with its target. These are clear breakthroughs in the understanding of DENV C-LDs interaction (and inhibition), providing a ground for the development of C protein targeted treatments for the infections by DENV and other Flavivirus