Abstract
Analysis of the tsetse fly salivary gland EST database revealed the presence of a highly enriched cluster of putative endonuclease genes, including tsal1 and tsal2. Tsal proteins are the major components of tsetse fly (G. morsitans morsitans) saliva where they are present as monomers as well as high molecular weight complexes with other saliva proteins. We demonstrate that the recombinant tsetse salivary gland proteins 1&2 (Tsal1&2) display DNA/RNA non-specific, high affinity nucleic acid binding with KD values in the low nanomolar range and a non-exclusive preference for duplex. These Tsal proteins exert only a residual nuclease activity with a preference for dsDNA in a broad pH range. Knockdown of Tsal expression by in vivo RNA interference in the tsetse fly revealed a partially impaired blood digestion phenotype as evidenced by higher gut nucleic acid, hematin and protein contents.
Highlights
Tsetse flies (Glossina sp.) are obligate blood feeding insects that transmit protozoan parasites (Trypanosoma sp.), the etiological agents of African trypanosomiasis
Most residues predicted to be important in the active site (Figure 1A, box) for structure determination, substrate and cofactor binding of the archetypical Serratia marcescens and the M. japonicus nuclease [19,20] are conserved in tsetse salivary gland protein 1 (Tsal1) and Tsal2 (Figure 1B)
A recurrent observation from in-depth transcriptome and proteome analyses in blood feeding arthropods is the putative presence of secreted endonucleases in the salivary glands
Summary
Tsetse flies (Glossina sp.) are obligate blood feeding insects that transmit protozoan parasites (Trypanosoma sp.), the etiological agents of African trypanosomiasis. During the probing and blood feeding interaction, tsetse flies inoculate a complex mixture of salivary components from which the composition has been explored by proteome and transcriptome analyses as well as by functional genomics approaches [1,2,3,4,5,6,7]. Beside interfering with host hemostasis, saliva is highly immunogenic/allergenic in nature [2,10,11] and was documented to modulate host inflammatory reactions against the trypanosome, thereby promoting infection onset [12]. This implies that salivary compounds contribute to the feeding event and can be considered as vector-derived virulence factors
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