Genome Wide Mapping of Peptidases in Rhodnius prolixus: Identification of Protease Gene Duplications, Horizontally Transferred Proteases and Analysis of Peptidase A1 Structures, with Considerations on Their Role in the Evolution of Hematophagy in Triatominae.

Bianca S Henriques,Roderick J Dillon,Caroline Da Silva Moraes,Fernando A Genta,Rafael D Mesquita,Patricia Azambuja,Eloi De Souza Garcia,Samara G Da Costa,Bruno Gomes,Viv M Dillon

doi:10.3389/fphys.2017.01051

Abstract

Triatominae is a subfamily of the order Hemiptera whose species are able to feed in the vertebrate blood (i.e., hematophagy). This feeding behavior presents a great physiological challenge to insects, especially in Hemipteran species with a digestion performed by lysosomal-like cathepsins instead of the more common trypsin-like enzymes. With the aim of having a deeper understanding of protease involvement in the evolutionary adaptation for hematophagy in Hemipterans, we screened peptidases in the Rhodnius prolixus genome and characterized them using common blast (NCBI) and conserved domain analyses (HMMER/blast manager software, FAT, plus PFAM database). We compared the results with available sequences from other hemipteran species and with 18 arthropod genomes present in the MEROPS database. Rhodnius prolixus contains at least 433 protease coding genes, belonging to 71 protease families. Seven peptidase families in R. prolixus presented higher gene numbers when compared to other arthropod genomes. Further analysis indicated that a gene expansion of the protease family A1 (Eukaryotic aspartyl protease, PF00026) might have played a major role in the adaptation to hematophagy since most of these peptidase genes seem to be recently acquired, are expressed in the gut and present putative secretory pathway signal peptides. Besides that, most R. prolixus A1 peptidases showed high frequencies of basic residues at the protein surface, a typical structural signature of Cathepsin D-like proteins. Other peptidase families expanded in R. prolixus (i.e., C2 and M17) also presented significant differences between hematophagous (higher number of peptidases) and non-hematophagous species. This study also provides evidence for gene acquisition from microorganisms in some peptidase families in R. prolixus: (1) family M74 (murein endopeptidase), (2) family S29 (Hepatitis C virus NS3 protease), and (3) family S24 (repressor LexA). This study revealed new targets for studying the adaptation of these insects for digestion of blood meals and their competence as vectors of Chagas disease.

Highlights

The arthropod development requires several nutritional components that are usually obtained through the digestive function
We initially found 23 hits belonging to the peptidase family A1 in R. prolixus genome (Supplementary Table 5)
The number and diversity of peptidases found in R. prolixus (i.e., 433 protease coding genes from 71 peptidase families, item 1 of Results section) are within normal values found in arthropods

Summary

Introduction

The arthropod development requires several nutritional components that are usually obtained through the digestive function. In this process, enzymes are crucial to break down complex compounds into simpler molecules that can be absorbed by the organism to be used for energy, growth, or reproduction. The molecular properties of these enzymes differ among arthropod taxa and are especially correlated to their phylogenetic background Other factors such as the adaptation to new feeding resources may have influenced the pre-established composition of enzymes in closely related organisms (Terra and Ferreira, 2005). Hematophagy (i.e., ability in feeding on vertebrate blood) potentiates the ingestion of high amounts of proteins in short time by arthropods. The heme molecule released by digestion of hemoglobin in hematophagous is toxic and result in oxidative stress to the midgut cells (Graça-Souza et al, 2006)

Methods

Results

Conclusion