Abstract:
Tick saliva contains a complexmixture of peptides and non-peptides that counteract their
hosts’ hemostasis, immunity, and tissue-repair reactions. Recent transcriptomic studies
have revealed over one thousand different transcripts coding for secreted polypeptides in
a single tick species. Not only do these gene products belong tomany expanded families,
such as the lipocalins, metalloproteases, Antigen-5, cystatins, and apyrases, but also
families that are found exclusively in ticks, such as the evasins, Isac, DAP36, and many
others. Phylogenetic analysis of the deduced protein sequences indicate that the salivary
genes exhibit an increased rate of evolution due to a lower evolutionary constraint and/or
positive selection, allowing for a large diversity of tick salivary proteins. Thus, for each new
tick species that has its salivary transcriptome sequenced and assembled, a formidable
task of annotation of these transcripts awaits. Currently, as of November 2019, there are
over 287 thousand coding sequences deposited at the National Center for Biotechnology
Information (NCBI) that are derived from tick salivary gland mRNA. Here, from these 287
thousand sequences we identified 45,264 potential secretory proteins which possess
a signal peptide and no transmembrane domains on the mature peptide. By using
the psiblast tools, position-specific matrices were constructed and assembled into
the TickSialoFam (TSF) database. The TSF is a rpsblastable database that can help
with the annotation of tick sialotranscriptomes. The TSA database identified 136 tick
salivary secreted protein families, as well as 80 families of endosomal-related products,
mostly having a protein modification function. As the number of sequences increases,
and new annotation details become available, new releases of the TSF database may
become available.
