Biochemical Study of a Chymotrypsin-like Serine Protease, AaCHYMO, from the Female Aedes Aegypti Mosquito

Abstract

The Aedes aegypti female mosquito is a dominant vector of four bloodborne viruses: dengue, chikungunya, yellow fever, and Zika. Defenses against viral infection are reliant on human competence to limit interactions with the vector or through abatement using methods that are either too expensive or ecologically invasive upon other species. An alternative vector control approach focuses specifically on blood meal protein digestion, which is a required process to fuel the gonotrophic cycle. Reduction of eggs laid can be observed by inhibiting midgut serine proteases that are afterward released in the midgut in the presence of a blood meal. Trypsin-like serine proteases are the major enzymes involved in bloodmeal protein digestion and have been the focus of study in the 1990s. However, the study of chymotrypsin-like serine proteases has been neglected; therefore, the focus of this work will be on AaCHYMO, a chymotrypsin-like serine protease first identified in 1996. To understand the role of this protease in the blood meal digestion process, we must isolate and study the chymotrypsin in vitro. For the first time, recombinant AaCHYMO has been recombinantly expressed solubly in bacteria, and more surprisingly, the zymogen form of the enzyme is autocatalytic and has enough activity to cleave a well-known chymotrypsin-like substrate (Suc-Ala-Ala-Pro-Phe-pNA). This activity may be novel since autocatalytic behavior in chymotrypsin-like proteases is not commonly found in both vertebrate and invertebrate organisms.