STRUCTURAL AND FUNCTIONAL STUDIES ON AaTI-PLASMIN-DENV INTERACTION REVEALS SPECIFICITIES OF KAZAL-TYPE INHIBITORS

Abstract

The fitness of vector- borne viruses like dengue virus (DENV) is dependent on the ability to breach midgut barriers. Previous findings show that Aedes aegypti mosquitos fed with plasmin containing bloodmeal have significantly higher dengue viral (DENV) titres, and this effect is blocked by a Kazal-type plasmin inhibitor called AaTI, expressed constitutively in the midgut. However, the precise mechanism of tripartite interaction among AaTI-plasmin-DENV has not been expounded. We studied DENV recruitment of plasmin proteolysis using FITC-dextran molecules and found that DENV hijacks plasmin proteolytic activity to evade midgut infection barrier, and this is reverted by AaTI. Using biolayer interferometry, we found that plasmin binds to domain-I/II of DENV envelope protein. To understand how AaTI blocks plasmin activity, we solved the complex crystal structure of serine protease domain of plasmin, with AaTI at 1.90 Å resolution, and compared reactivities of AaTI with other Kazal-type inhibitors like Infestin-1 and Infestin-4.