The Function and Three-Dimensional Structure of a Thromboxane A2/Cysteinyl Leukotriene-Binding Protein from the Saliva of a Mosquito Vector of the Malaria Parasite

Patricia H Alvarenga,John F Andersen,José M C Ribeiro,Ivo M B Francischetti,Eric Calvo,Anderson Sá-Nunes,David S Schneider

doi:10.1371/journal.pbio.1000547

Abstract

Author SummaryWhen feeding, a female mosquito must inhibit the blood clotting and inflammatory responses of the host. To do this, the insect produces salivary proteins that neutralize key host molecules participating in clotting and inflammation. Here, we describe a salivary protein AnSt-D7L1 that scavenges both thomboxane A2 and cysteinyl leukotrienes, two substances involved in blood vessel constriction, platelet aggregation, and inflammatory responses to an insect bite. We produced this protein in bacteria and showed that it tightly binds both these molecules, inhibiting the processes in which they are involved. We then determined its structure using X-ray crystallography and showed that there is a single binding site in one domain of the protein, accommodating both thromboxane A2 and cysteinyl leukotrienes, and that this site is responsible for the scavenging effect of the protein. These studies reveal the structural features of proteins needed to bind to key molecules of potential pharmacological importance and add to our understanding of the process of mosquito blood feeding, which is essential for transmission of the malaria parasite.

Highlights

Hematophagous arthropods produce a varied mix of salivary proteins, peptides, and small molecules aimed at overcoming the hemostatic and inflammatory responses of the host
We describe a salivary protein AnSt-D7L1 that scavenges both thomboxane A2 and cysteinyl leukotrienes, two substances involved in blood vessel constriction, platelet aggregation, and inflammatory responses to an insect bite
We determined its structure using X-ray crystallography and showed that there is a single binding site in one domain of the protein, accommodating both thromboxane A2 and cysteinyl leukotrienes, and that this site is responsible for the scavenging effect of the protein

Summary

Introduction

Hematophagous arthropods produce a varied mix of salivary proteins, peptides, and small molecules aimed at overcoming the hemostatic and inflammatory responses of the host. Inflammation in the skin at the site of feeding has been shown to influence the establishment of infection by arthropod-vectored pathogens, making the anti-inflammatory components of saliva important from this standpoint as well [5,6]. Several pathogens take advantage of the biological properties of the salivary mixture to infect their hosts and cause disease. It has been demonstrated that immunity against salivary components from different mosquito species is able to reduce disease transmission by these vectors [7,8,9,10]. The mosquito life cycle is affected by immunization against salivary molecules [11]

Methods

Results

Discussion

Conclusion