Abstract
BackgroundAntibody responses against Anopheles salivary proteins can indicate individual exposure to bites of malaria vectors. The extent to which these salivary proteins are species-specific is not entirely resolved. Thus, a better knowledge of the diversity among salivary protein repertoires from various malaria vector species is necessary to select relevant genus-, subgenus- and/or species-specific salivary antigens. Such antigens could be used for quantitative (mosquito density) and qualitative (mosquito species) immunological evaluation of malaria vectors/host contact. In this study, salivary gland protein repertoires (sialomes) from several Anopheles species were compared using in silico analysis and proteomics. The antigenic diversity of salivary gland proteins among different Anopheles species was also examined.ResultsIn silico analysis of secreted salivary gland protein sequences retrieved from an NCBInr database of six Anopheles species belonging to the Cellia subgenus (An. gambiae, An. arabiensis, An. stephensi and An. funestus) and Nyssorhynchus subgenus (An. albimanus and An. darlingi) displayed a higher degree of similarity compared to salivary proteins from closely related Anopheles species. Additionally, computational hierarchical clustering allowed identification of genus-, subgenus- and species-specific salivary proteins. Proteomic and immunoblot analyses performed on salivary gland extracts from four Anopheles species (An. gambiae, An. arabiensis, An. stephensi and An. albimanus) indicated that heterogeneity of the salivary proteome and antigenic proteins was lower among closely related anopheline species and increased with phylogenetic distance.ConclusionThis is the first report on the diversity of the salivary protein repertoire among species from the Anopheles genus at the protein level. This work demonstrates that a molecular diversity is exhibited among salivary proteins from closely related species despite their common pharmacological activities. The involvement of these proteins as antigenic candidates for genus-, subgenus- or species-specific immunological evaluation of individual exposure to Anopheles bites is discussed.
Highlights
Antibody responses against Anopheles salivary proteins can indicate individual exposure to bites of malaria vectors
A bootstrap consensus tree inferred from 10,000 replicates showed that the six Anopheles species are divided into the following two major groups based on their taxonomic classification: (i) a clade formed by An. gambiae, An. arabiensis, An. funestus and An. stephensi, which are all members of the Cellia subgenus; and (ii) a clade including An. albimanus and An. darlingi, which are two neotropical species belonging to the Nyssorhynchus subgenus
In silico analysis of secreted salivary protein sequences from the six Anopheles species tested in the present study indicated that secreted salivary proteins sharing between 70% and 90% amino acid sequence identity are mainly clustered according to their subgenus affiliation
Summary
Antibody responses against Anopheles salivary proteins can indicate individual exposure to bites of malaria vectors. Availability of the genome sequence of several arthropods of major health importance [44,45], combined with transcriptomic and proteomic analyses of their salivary gland extracts (SGEs) [46,47,48,49,50,51,52,53,54] have provided new insight into the diversity of salivary molecules among various hematophagous arthropods [55] These studies revealed a number of secreted protein families, potentially involved in haematophagy or sugar digestion, that are ubiquitous in the Nematocera suborder. Sialome diversity among these different anopheline species is poorly documented at the molecular and antigenic levels
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