An Overview of D7 Protein Structure and Physiological Roles in Blood-Feeding Nematocera

SIMPLE SUMMARY: Vectors are organisms that can transmit infectious pathogens from a host (human or animal) to another. Many vectors (including mosquitoes, sand flies and ticks) have one common characteristic: they are blood-feeding (hematophagous) arthropods. Every time they bite their vertebrate host, skin and vascular injury triggers a series of responses that in place could lead to interruption of blood flow to their mouthparts, and to host awareness due to itching and pain. Nevertheless, their saliva contains a cocktail of molecules capable to counteract these host responses (hemostasis, inflammation and immunity), allowing them to feed successfully. Many times, the pathogens they transmit are injected in the host with the saliva. Therefore, understanding the composition of vector’s saliva is crucial to study their biology, their vectorial capacity, as well as to propose new methods to control the diseases they transmit (including new vaccine candidates). Among important salivary protein families is the D7, abundantly expressed in bloodsucking Diptera and distantly related to Odorant-Binding Proteins (OBP). Here, we provide an extensive review of D7 proteins structure, function and evolution, discussing how gene duplication and modifications in their OBP-like domains lead to gain and loss of function in different hematophagous Diptera species. ABSTRACT: Each time an insect bites a vertebrate host, skin and vascular injury caused by piercing triggers a series of responses including hemostasis, inflammation and immunity. In place, this set of redundant and interconnected responses would ultimately cause blood coagulation, itching and pain leading to host awareness, resulting in feeding interruption in the best-case scenario. Nevertheless, hematophagous arthropod saliva contains a complex cocktail of molecules that are crucial to the success of blood-feeding. Among important protein families described so far in the saliva of blood sucking arthropods, is the D7, abundantly expressed in blood feeding Nematocera. D7 proteins are distantly related to insect Odorant-Binding Proteins (OBP), and despite low sequence identity, observation of structural similarity led to the suggestion that like OBPs, they should bind/sequester small hydrophobic compounds. Members belonging to this family are divided in short forms and long forms, containing one or two OBP-like domains, respectively. Here, we provide a review of D7 proteins structure and function, discussing how gene duplication and some modifications in their OBP-like domains during the course of evolution lead to gain and loss of function among different hematophagous Diptera species.